Space Climate 10

8 Jun 2026, 17:55 → 12 Jun 2026, 21:00 Europe/Mariehamn

NB: Please do not use the Indico page to upload presentations. This will be done on-site.

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Monday 8 June

18:00 → 21:00 Voice breaking party led by Prof. Kalevi Mursula (registration via email spaceclimate10@gmail.com before 1 June)

Please sent email spaceclimate10@gmail.com by June 1 , as the number of places is limited.

Come to the DINO’S BAR & GRILL, grab a drink and join us for an informal evening of singing, light conversation, and new connections - the perfect way to set the mood before the SC 10 begins.

Tuesday 9 June

09:00 → 09:45 Registration and Presentation collection (please prepare your file in .pdf or .pptx) during morning coffee

09:45 → 10:00 Opening ceremony + Acknowledgements

10:00 → 10:30 Long-term evolution of the magnetic field in the inner heliosphere

The development of our understanding of long-term change in the magnetic field of the inner heliosphere will be reviewed. The basic technique is to use modern understanding from space age observations and numerical models, with available proxy indicators, such as historic observations of sunspots, geomagnetic activity, aurorae, eclipses, polar faculae, and polar crown filaments. In addition, cosmogenic isotope abundances in various terrestrial reservoirs can be used to constrain variations and extend them back to times before observations were routinely recorded. The various techniques show a considerable convergence in annual means but evaluation of major space weather events remains difficult and depends on the metrics used to quantify them.

Speaker: Prof. Mike Lockwood (Reading U., UK)

10:30 → 11:58 1.1 Dynamo (chair Kalevi Mursula)

Convener: Paul Charbonneau (Université de Montréal, Montréal, Canada)

10:30 Solar Dynamo as the Driver of Space Climate

Decadal-scale and longer-term variations in space environmental conditions forces planetary systems such as the Earth. These variations in radiation, particle and magnetic flux, and occasion extreme events, have a profound influence on planets, including but not limited to atmospheric evolution, climate dynamics, and technological impacts. Studies from the Sun-Earth system indicate that the typical space climate forcing parameters such as the solar radiation, heliospheric magnetic flux, solar wind, solar energetic events, and indeed the galactic cosmic ray flux are all modulated by the emergence and evolution of magnetic fields on the Sun’s surface. The latter in turn is governed by the output of the solar dynamo mechanism which has its origin in magnetohydrodynamic processes in the solar interior. Magnetic fields therefore act as a bridge, causally connecting the interior of a star to the space climate of planets that it hosts. In this talk, I shall highlight some of the important drivers of planetary space environments and trace their origin to decadal, centennial and longer scale fluctuations in the solar dynamo mechanism – emphasizing the rich physics at play that determines the ultimate origin of space climate.

Speaker: Prof. Dibyendu Nandi (IISER, IN)

10:50 Fluctuations in Babcock-Leighton dynamos: magnetic backreaction on differential rotation and long-term amplitude modulation

The predominant magnetic backreaction channel through which the growth of solar/stellar dynamos is stabilized has not yet been identified with confidence. In this work, we investigate the dynamical feedback on differential rotation directly driven by the Lorentz force associated with the cycling large-scale magnetic field, in an otherwise kinematic dynamo model where the Babcock-Leighton mechanism is used to regenerate the large-scale dipole. We explore the dynamical regimes in which this saturation occurs efficiently and find that a very weak reduction of the average differential rotation, and even weaker torsional oscillation patterns, are sufficient to stabilize the dynamo, from weakly to highly supercritical dynamo solutions, as well as for Prandtl numbers approaching unity. Acting jointly with the time-delay dynamics that characterize flux- transport dynamos operating in or close to the advection-dominated regime, the dynamical feedback produces a variety of deterministic long-timescale modulations that are strongly enhanced by stochastic forcing. As such, an accurate characterization of long- timescale solar activity modulations, as obtained from cosmogenic isotopes, can provide useful constraints on the saturation mechanism(s) of solar and stellar dynamos.

Speaker: Dr Alexandre Lemerle (Université de Montréal, CA)

11:10 A qualitative model for the occurrence of grand minima based on superadiabaticity perturbations in the tachocline

The study of cosmogenic radionuclides shows that an event of significantly reduced solar activity such as the Maunder Minimum (1645-1715) was not an exceptional event, but is a recurring phenomenon in the history of solar magnetic activity.
Although various ideas have been proposed to try to explain why Grand Minima occur, there is no satisfactory model yet.
Since the decade of 1980 many astrophysicists believe that the tachocline plays a fundamental role in the generation and storage of the toroidal mag- netic flux that eventually becomes unstable and buoyantly rises to emerge at the stellar surface producing sunspots.
I will address the role of the thermodynamic properties (and more specifi- cally, the entropy stratification) of the tachocline in determining the stability of magnetic structures and, therefore, its capability to store magnetic flux. The entropy stratification is quantified by a dimensionless quantity called the superadiabaticity, δ. Tiny variations in δ (of the order of one part in 104 or less) may determine global properties of the magnetic field at the solar surface. The maximuum field-strength of toroidal flux tubes that can be stored in mechanical equilibrium at the bottom of the convection zone is very sensitive to the value of δ. The connection between temporal vari- ations in δ (which would alter the storage capacity of the tachocline) with the occurence of Maunder-minimum-like episodes will be discussed.
I will briefly address the possible role of stochastic resonance in amplifying weak signals up to a level that can affect the long-term magnetic activity by switching between two states of a bistable system, corresponding to weak- field and strong-field regimes.
The approach would be applicable to any rotating star with a radiative zone surrounded by a convection zone.

Speaker: Prof. Antonio Ferriz-Mas (University of Vigo and IAA-CSIC, ES)

11:22 Uncovering the small-scale footprint of the global solar dynamo

Small-scale magnetic elements are ubiquitous in the solar photosphere, covering significant portions of the Sun’s visible surface and organizing into the so-called magnetic network. Advected and jostled by the turbulent plasma in which they are embedded, these elements constitute an ideal proxy to study the superficial flows of the Sun’s convective envelope. Furthermore, they act as a prime conduit for the transfer of wave energy from the lower layers of the solar atmosphere to the corona, contributing to the acceleration of the solar wind. Leveraging long-term, stable, and continuous observations of the Sun’s magnetic field from the Helioseismic and Magnetic Imager onboard NASA’s Solar Dynamics Observatory, we tracked more than 100 million small-scale magnetic elements on the Sun’s surface using our novel Solar Feature Tracking suite. Spanning one and a half solar cycles, this represents the largest statistical analysis of its kind. Given the distinctly different properties of the sampled elements, we argue that their observed shared behaviours, modulated by the solar cycle, can only be attributed to a much closer interaction between scales than previously anticipated.

Speaker: Mr Michele Berretti (Rome Tor Vergata U., IT)

11:34 Historical Eclipse Reports as Spot References for Space Climatology Back to 709 BCE

Some of the participants might be preparing scientific measurements, experiments, or campaigns for the total solar eclipses this August or/and next August. We have good reason for such campaigns, as total solar eclipses have been not only astronomical spectacles but also astrophysical laboratories throughout human history. These astronomical spectacles serve as spot references for the variability of the solar atmosphere, the coronal dynamics, the solar radius, and the Earth's rotation speed -- even without expensive spacecrafts. Looking back the human history, even on a datable basis, reported total solar eclipses have been confirmed since 709 BCE and extend their chronology centuries or even millennia beyond the coverage of the space age. Their chronological coverage is even longer than that of instrumental sunspot observations (since 1607) and particularly unique for the direct solar observations. Some of such eclipse records involve indications of morphology of the coronal structure and can be used as spot references for the solar-cycle phases. These records offer valuable spot reference for the space climatology even before the telescopic observations. This presentation aims at showing some case studies on their use before the space age, especially in terms of our analyses on the coronal morphology and the latitudinal extents of the streamerbelts. Particular emphases are placed on those in the grand solar minima and pre-telescopic ages. We examine their chronology and case studies back to 709 BCE on the basis of original historical records (e.g., Hayakawa et al., 2025, ApJL, 995, L1), in comparison with Usoskin et al.'s recent radiocarbon-based solar-cycle reconstructions with an annual resolution. Our results serve as independent reference to confirm and examine the recent solar cycle reconstructions for the last three millennia.

Speaker: Prof. Hisashi Hayakawa (Nagoya U., JP)

11:46 Magnetic Variability of Solar-Like Stars Extends Far Beyond the Solar Range

We constructed a comprehensive sample of solar-like stars by combining Kepler, Gaia, and LAMOST data, selecting stars with near-solar fundamental parameters and measured rotation periods. The rotation periods were determined using a method specifically designed to recover signals from relatively old and weakly active stars.
We find that the majority of solar-like stars exhibit photometric variability within the range observed for the Sun. However, we identify a subgroup of roughly 400 stars that are nearly indistinguishable from the Sun in their basic properties, yet display significantly enhanced variability. In addition, we detect superflares on approximately 2500 solar-like stars.
These results can be interpreted in two ways: either subtle, yet unidentified physical differences separate the highly variable stars from those with near-solar variability, or both groups represent the intrinsic range of magnetic activity states accessible to Sun-like stars. In the latter case, the Sun may currently be in a relatively quiet phase and could, in principle, undergo epochs of substantially elevated variability.

Speaker: Alexander Shapiro (University of Graz, AT)

11:58 → 13:00 Poster session

12:00 P1 Synchronisation Model of the Solar Dynamo

We present a solar dynamo model that appears capable of explaining various periodicities across a wide range of timescales in a self-consistent manner [1]. Starting with Rieger-type periodicities, we demonstrate that the two-planet spring tides of Venus, Earth, and Jupiter can excite magneto-Rossby waves in the solar tachocline. These waves have typical periods ranging from 100 to 300 days, and can reach amplitudes of metres per second or greater [2,3].
The first beat period, derived from the three tidally-excited waves, is 1.723 years. This aligns remarkably well with the observed period of the quasi-biennial oscillation (QBO) [1, 4]. The QBO could also help explain the astonishing regularity and calmness of the solar dynamo, a long-standing mystery.
The second beat period of 11.07 years, which arises from these three waves, corresponds to the long-term mean value of the Schwabe cycle. We hypothesise that the axisymmetric component of the α-effect, caused by these waves, is strong enough to synchronise the entire solar dynamo via parametric resonance [5].
Finally, we demonstrate that another beat, occurring between the 22.14-year Hale cycle and the Sun's 19.86-year periodic motion around the solar system's barycentre, could account for the Suess-de Vries cycle, which has a period of 193 years. The resulting spectrum of this double-synchronised dynamo model is found to be in very good agreement with climate-related data obtained from varved sediments in the Lake Lisan region [3, 6].

References
[1] Stefani, F. et al., Solar Phys. 300, 110 2025.
[2] Horstmann, G.M. et al., Astrophys. J. 944, 48 (2023)
[3] Stefani, F. et al., Solar Phys. 299, 51 (2024)
[4] Stefani, F. et al., https://arxiv.org/abs/2602.11227 (2026)
[5] Klevs M. et al. Solar Phys. 298, 90 (2023)
[6] Prasad, S. et al., Geology 32, 581 (2004)

Speaker: Frank Stefani (Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, D-01328 Dresden, Germany)

12:01 P2 - Inverting the Solar Meridional Circulation Profile in a Babcock-Leighton Flux Transport Dynamo Model through Genetic Modelling

The magnetohydrodynamic dynamo effect, which governs the interactions between internal solar fluid flows and magnetic fields, drives the Sun’s 11-year activity cycle. The meridional circulation, a key aspect of this process, plays a crucial role in regulating the solar cycle and its large-scale magnetic field, particularly within the framework of flux transport dynamo models. However, the deep internal profile of this large-scale flow remains challenging to observe, poorly constrained, and heavily debated.
In this work, we use the evolution of the Sun’s surface magnetic flux to constrain the internal profile of the meridional circulation. To achieve this, we developed a highly flexible basis of nearly orthogonal functions constructed from Legendre and Chebyshev polynomials to describe the latitu- dinal and radial dependencies of the flow, enabling the generation of complex circulation geometries. By combining these functions with weights optimized via a genetic algorithm, this versatile frame- work can adequately reproduce most kinematic profiles used in existing dynamo models, as well as more complex multicellular flow patterns, including, for example, small secondary flow cells located in depth and/or latitude.
Building on this mathematical foundation, we formulate an inversion problem to map the inter- nal meridional flow in a Babcock-Leighton flux transport dynamo model. Using a robust genetic algorithm, the flow is inverted by constraining the time-latitude structure of the deep toroidal mag- netic field to fit the shape of the observed surface butterfly diagram, and the surface magnetograms produced by our model to fit observed surface magnetic data.
This optimization process explores a complex, multimodal parameter space to identify not merely a single optimal parameter set, but rather a remarkably diverse population of statistically acceptable meridional circulation profiles. Notably, this ensemble includes complex, multiple-cell circulation patterns. Despite their internal topological differences, all accepted profiles successfully reproduce the fundamental characteristics of solar magnetism and match observed surface data. These results highlight the intrinsic degeneracy in inferring deep solar flows from surface magnetic evolution. Consequences for dynamo-based solar cycle prediction schemes will be briefly discussed.

Speaker: Laurie Lamy-Proulx (Université de Montréal, Montréal, Canada)

12:02 P3 - Exploring the Dominant Process of Solar Toroidal Magnetic Flux Loss

As the solar magnetic cycle evolves, subsurface toroidal magnetic flux is systematically generated and lost, and this work aims to identify the dominant process behind the flux loss. By employing a data-driven dynamo model and holding surface magnetic flux transport identical across the cycles 12-21, we conducted numerical experiments to isolate and assess the loss of subsurface toroidal flux, and then compared the results with two observational constraints: the butterfly diagram and the observed correlation between the polar field at cycle minimum and the strength of the next cycle. We found that under weak bulk diffusivity, the loss of the previous cycle's toroidal flux is dominated by cancellation with newly generated flux, causing the new cycle's actual flux to differ from its generated value and thereby preventing the simulation of the observed polar field-cycle strength correlation. When diffusivity is increased to a level where it dominates flux loss, residual flux is more effectively removed, restoring the polar field cycle strength correlation, yet operating in the diffusion-dominated regime suppresses the formation of the butterfly diagram. In contrast, active region emergence acts as an efficient mechanism for removing residual flux, and when it dominates the flux loss, both the correlation and the butterfly diagram are successfully reproduced. Thus, we conclude that active region emergence dominates the subsurface toroidal flux loss.

Speaker: Zebin Zhang (Institute of Frontier and Interdisciplinary Science and Institute of Space Sciences, Shandong University, People's Republic of China)

12:03 P4 - Stellar flares and starspots in TESS light curves

Stellar magnetic activity causes different observable phenomena on a stellar surface from dark spots to bright and explosive events, such as flares and coronal mass ejections. Both flares and starspots induce variations in stellar brightness, which can be seen in light curves. Starspots and stellar rotation together produce periodic dimmings of a star, whereas flares cause sudden and irregular brightenings as they release magnetic energy into a stellar atmosphere. Flares can have significant influence on planetary environments and consequently on the habitability of planets. The presented research focuses on late-type stars (spectral types F, G, K, and M), which have convective envelopes and are therefore expected to be magnetically active. We examine flares from seven late-type stars and assess their possible connection to starspots. Data from the Transiting Exoplanet Survey Satellite (TESS) are used in the analysis. Flares are identified from light curves using a flare detection program based on a machine learning algorithm. The timings of flares are compared to the stellar brightness trend in order to reveal a possible correlation between the flare occurrence and the stellar rotational phase.

Speaker: Emilia Rintamäki (Department of Physics, University of Helsinki)

12:04 P5 - Properties of Circumfacular regions derived from Hα and Ca II K synoptic observations

Circumfacular regions are dark structures surrounding active regions that appear in chromospheric observations, yet their physical properties and role in solar variability remain poorly constrained. Using ChroTel synoptic observations in Hα and Ca II K spanning the maximum of solar cycle 24 to the onset of cycle 25, we derive the photometric and geometric properties of circumfacular regions and compare them with plages, sunspots, and filaments. This study provides the most comprehensive characterization of circumfacular regions to date. We introduce a circumfacular photometric index and show that it is strongly correlated with established solar-activity proxies, with temporal variability primarily driven by changes in area coverage. The strength of these correlations evolves with the global activity level. We discuss the implications of these results for the interpretation of Balmer-line variability in the Sun and solar-like stars.

Speaker: Serena Criscuoli (NSO, US)

12:05 P6 - Total Solar Irradiance Variations Based on Fengyun3 Series Satellites

Solar irradiance observation is one of main objectives of Fengyun-3 (FY-3) series since the launch of first satellite FY-3A in 2008. For total solar irradiance (TSI), there are six satellites with the payload named Solar Irradiance Monitor (SIM) to perform operational observation. The performance of the instrument is gradually improving at the step of SIM-I, SIM-II and SIM-III. The SIM-III is scheduled for launch at the end of 2026. We recalibrate the early-stage data of SIM to build a dataset with the same scale and evaluate the TSI variations.

Speaker: Jin Qi (National Satellite Meteorological Center, China)

12:06 P7 - Quantifying the effect of passband on observations in the Ca ii K line

Solar irradiance is one of the key external forcing agents of Earth’s climate. Quantifying the effect of its variability requires knowledge of past irradiance changes over as long timescales as possible. Since direct space-based measurements are available for less than half a century, this necessitates irradiance reconstructions using models. On climate-relevant timescales, irradiance variability is driven by the evolution of the solar surface magnetic field. While most existing historical reconstructions are based on sunspot records, these provide limited information on the long-term evolution of bright magnetic features (faculae or plage), which is the main source of uncertainty in estimates of secular irradiance changes. Independent constraints on past solar magnetic activity are therefore essential.
One such proxy is the brightness of the Sun in the Ca II K spectral line. Full-disc Ca II K images have been taken since 1892 at multiple observatories worldwide, with individual archives covering different time intervals. Combining these data offers the potential to track changes in solar surface magnetism, and thus irradiance, over more than a century. However, this requires careful crosscalibration to account for differences in instruments and observational settings, in particular the varying spectral passbands used across and within archives.
To study the effect of different passbands on Ca II K observations, we use recent high spectral- and spatial-resolution data from the balloon-borne observatory Sunrise iii. By emulating different passbands of historical archives, we study how the observed Ca II K intensity depends on this choice. These results provide a basis for a cross-calibration of various historical Ca II K datasets and for improving constraints on long-term solar irradiance variability.

Co-author list:
Theodosios Chatzistergos (1), Natalie Krivova (1), Sami K. Solanki (1), Francisco A. Iglesias (1,2), Ilaria Ermolli (3), Andreas Lagg (1), Achim Gandorfer (1), Jose Carlos del Toro Iniesta (4,5), Yukio Katsukawa (6,7,8), Pietro Bernasconi (9), Thomas Berkefeld (10), Alex Feller (1), Tino L. Riethmüller (1), Alberto Álvarez-Herrero (11,5), Masahito Kubo (6), H. N. Smitha (1), David Orozco Suárez (4,5), Bianca Grauf (1), Michael Carpenter (9), Alexander Bell (10), Valentín Martínez Pillet (12,5), Laurent Gizon (1,13), Johannes Hoelken (1), Francisco Javier Bailén (4,5), Julian Blanco Rodríguez (14,5), Juan Sebastián Castellanos Durán (1), Edvarda Harnes (1), Ryohtaroh T. Ishikawa (15), Yusuke Kawabata (6), Takuma Matsumoto (16), Takayoshi Obal (7,1), Azaymi L. Siu‑Tapia (4,5), Hanna Strecker (4,5), Dušan Vukadinović (18,1), Yasuhito Narita (19,1)
1 Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
2 Grupo de Estudios en Heliofísica de Mendoza, CONICET, Universidad de Mendoza, 5500 Mendoza, Argentina
3 INAF Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone, Italy
4 Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
5 Spanish Space Solar Physics Consortium
6 National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
7 Department of Earth and Planetary Science. The University of Tokvo. Tokvo 113-0033, Japan
8 The Graduate University for Actae Se es (SOKENDAL), Mitaka, Tokyo 1818588, Japan
9 Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
10 Institut für Sonnenphysik (KIS), Georges-Köhler-Allee 401a, 79110 Freiburg, Germany
11 Instituto Nacional de Técnica Aeroespacial (INTA), E-28850 Torrejón de Ardoz, Spain
12 Instituto de Astrofísica de Canarias, Vía Láctea, s/n, E-38205 La Laguna, Spain
13 Institut für Astrophysik und Geophysik, Georg-August-Universität Göttingen, Germany
14 Universitat de Valencia Catedrático José Beltrán 2, E-46980 Paterna-Valencia, Spain
15 National Institute for Fusion Science, 322-6 Oroshi-cho, Toki City 509-5292, Japan
16 ISEE, Nagoya University, Furocho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan
17 Advanced Research Center for Space Science and Technology, Kanazawa University, Japan
18 Institut für Physik, Universität Graz, Universitätsplatz 5, 8010 Graz, Austria
19 Institut für Theoretische Physik, TU Braunschweig, 38106 Braunschweig, Germany

Speaker: Theodosios Chatzistergos (Max Planck Institute for Solar System Research, DE)

12:07 P8 - Sunspot Number V2.0 Through Solar Cycle 25: A Long-term Multi-Proxy Stability Analysis

The International Sunspot Number (SN V2.0) is one of the longest and most detailed available series in astrophysics and its accuracy and stability is important for a large variety of scientific domains, not the least of which is the evolution of the Earth Climate.
Since its recalibration and release in 2015, SN V2.0 has been the subject of sustained scrutiny within the scientific community yet no community-wide audit has covered the first full decade of that recalibration through the rise of Solar Cycle 25. A systematic assessment of the long-term stability of SN V2.0 is thus in order. In parallel, the American Sunspot Number, which has been computed continuously since the mid-20th century, experienced documented inconsistencies in the 1990s, as highlighted in previous studies (Schaefer, 1997). However, a comprehensive evaluation of its long-term behavior in the subsequent decades is still lacking.
In this work, we analyze the temporal stability of SN V2.0 over multi-decadal timescales. We compare SILSO SN V2.0 with AAVSO Ra, and independent proxies such as Sunspot areas, F10.7, Nobeyama microwave fluxes, Mg II, ISGI aa, and SDO/HMI unsigned field to diagnose the long-term behavior of both indices. We examine their mutual consistency, sensitivity to calibration changes, and suitability for long-term comparative studies. This analysis allows us to assess the relative robustness of each index, identify potential residual biases, and evaluate their reliability for studies of long-term solar variability. We conclude by discussing implications for future sunspot number reconstructions and by outlining perspectives for maintaining stable, homogeneous solar activity indices over extended timescales.

Speaker: Kalugodu Chandrashekhar (Royal Observatory of Belgium, Solar Influences Data analysis Center (SIDC), Brussels, Belgium)

12:08 P9 - THE AAVSO DAILY SUNSPOT DATABASE 1945-2026

For consistent measures of solar activity over many cycles, the only possibility is the long historical record of sunspot counts made by human eyes looking through a telescope. For this we have records going back four centuries, but there are substantial problems with consistent calibration across many cycles. An independent data source is the large number of sunspot counts collected by the American Association of Variable Star Observers (AAVSO) for 1945-- 2026. The problem is that all the raw data for before 2001 has been lost. Fortunately, back in 1996, I copied a large batch of the original raw counts, covering 1945 to the mid-1970s. Further, I have collected from a wide range of sources the original raw counts for many long- term AAVSO observers from 1945--2001. I now have daily raw counts, with coverage over every year 1945 to present, with ~20 long-term observers covering each year. With this database, my goal is to provide a consistent calibration of sunspot counts over the last eight cycles. However, I would like the suggestions and advice of SPACE CLIMATE 10 attendees on the best method to combine these counts into a consistent whole. I propose a method where the long-term observers that cover one cycle are normalized then averaged on a day-by-day basis, creating a consistent count over the cycle. Multiple cycles are linked to a common calibration by the long-term observers that cover two-or-more cycles. However, I need suggestions and improvements, as well as community acceptance of the method.

Speaker: Bradley E. Schaefer (Louisiana State University)

12:09 P10 - Sunspot drawings analysis with DigiSun and estimation of the uncertainty on group positions

Sunspot drawings are a unique source of information to study the long-term manifestation of the magnetic activity on the solar surface. The Royal Observatory of Belgium (ROB) started such drawings around 1940 and continues today on a daily basis, making the whole collection spanning over more than 80 years.
In this presentation, we discuss two important limitations to the full scientific exploitation of sunspot drawings: (1) the need for a fast and reliable software to analyse the drawings and (2) an estimation of the inherent uncertainty, in particular in position calculations. In order to overcome the first issue, the use of a standard analysis tool for the parameter measurement would make it easier to analyse contemporary sunspot drawings. In addition, it would help to fill the inevitable gaps from a single observation station by merging homogeneous data. Secondly, obtaining an appropriate estimate of the uncertainty would give us more comprehensive information and enable us to combine measurements from different drawing collections.
In the first part of the presentation, we describe DigiSun, a software developed by our team for measuring ROB sunspot drawings and for creating a catalog of sunspots. An important feature is the calculation of a pixel-wise true area, corrected for foreshortening. This calculation is more precise than most current software, which only considers one centroid position to correct foreshortening. Another strength of DigiSun is its ability to handle different drawing formats, which allows it to analyse drawings from other collections. It has been shared with other observatories such as the Specola Observatory in Locarno since 2019, Tapei and Kandili since 2024. In addition, DigiSun can be used to analyse historical drawings and extend the series of detailed solar parameters further back in time.
In the second part of the presentation, we aim to improve our understanding of the source of uncertainty present in sunspot drawings and provide a first global estimate of it. We estimate the uncertainties in heliographic coordinates, which is a crucial factor in the analysis of long-term solar differential rotation and the distribution of heliographic longitude and latitude across various solar cycles.

Speaker: Sabrina Bechet (ROB)

12:10 P11 - New high-resolution 10Be and 36Cl measurements across key Holocene intervals

Constraining the magnitude and occurrence of extreme solar energetic particle (SEP) events beyond the instrumental era remains central to space climate research and risk assessment. Cosmogenic radionuclides archived in polar ice cores, particularly beryllium-$^{10}$ ($^{10}$Be) and chlorine-$^{36}$ ($^{36}$Cl), provide one of the few direct observational windows into past solar activity. Here we present new high resolution $^{10}$Be and $^{36}$Cl measurements from Greenland and Antarctic ice cores spanning three intervals of particular interest: (i) the Carrington event (1859 CE), (ii) the recently identified radionuclide event at 7,208-year Before Present, and (iii) the post bomb period, which serves as a benchmark for atmospheric transport and depositional processes under well constrained conditions. Across the Carrington interval, we did not observe a significant enhancement in $^{36}$Cl concentrations. This result implies either that no exceptionally large SEP event occurred or that associated particles did not intersect Earth. In contrast, the 7,208-year BP interval is robustly confirmed in both nuclides, allowing us to assess its fluence spectrum and relative magnitude. Finally, the post bomb data reveal a clear 11-year cyclicity in $^{36}$Cl concentrations and good agreement with the $^{10}$Be records from both hemispheres. Together, these results place new observational constraints on the sensitivity and limits of ice core radionuclide proxies for reconstructing extreme solar activity.

Co-author list:
C. I. Paleari (1), R. Muscheler (2), M. Christl (3), A. Smith (4), C. Vockenhuber (3)
(1) Department of Physical Geography and Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
(2) Department of Earth and Environmental Sciences, Lund University, Lund, Sweden
(3) ETH Zürich, Laboratory of Ion Beam Physics, Zürich, Switzerland
(4) Centre for Accelerator Science, ANSTO, Lucas Heights, NSW, Australia

Speaker: Florian Mekhaldi (Stockholm U., SE)

12:11 P12 - Solar and Climatic Imprints in a 10Be Record from the NEEM Ice Core (Greenland) over 0–1650 CE

Cosmogenic 10Be records from ice cores are important proxies for reconstructing past solar activity. However, the incorporation of the isotope signal in ice is influenced by atmospheric transport and position processes, which can complicate the interpretation of the signal. Combining data from multiple sites may help reduce such noise and enhance the robustness of 10Be-based solar activity reconstructions. In this study, we present a new 10Be record from the North Greenland Eemian Ice Drilling (NEEM) ice core covering the period of 0–1650 CE. We find good agreement between the NEEM 10Be record and other ice core 10Be records from Greenland and Antarctica, and tree-ring 14C data, suggesting a common production signal. This finding is important for estimating and synchronizing solar imprints on the isotope production. However, incorporating the NEEM 10Be record into a stacked ice core 10Be dataset does not significantly improve its correlation with 14C. This indicates that site-specific influences may still affect the record and partially obscure the common production signal. In addition, potential climatic influences on the NEEM 10Be record are investigated by comparing it with chemical ion data from the same site. This approach can help better identification of local versus regional influences on the isotope record.

Speaker: Prof. Ala Aldahan (Department of Geosciences, United Arab Emirates University, Al Ain, United Arab Emirates)

12:12 P13 - Radiocarbon Measurements over the Proposed Solar Energetic Particle Events in the 13th Century CE

Several globally synchronous spikes in radiocarbon production have now been detected in known-age tree-ring archives. Such occurrences, commonly known a Miyake events, must have been prompted by enormous bursts of cosmic radiation. Extreme storms on the Sun are widely believed to be the ultimate source of this radiation. Indeed, the phenomena are expected to be akin to scaled-up versions of modern ground level enhancements (GLEs). Usoskin and Kovaltsov (2021) attempted to relate GLEs to Miyake events by way of a best-fit Weibull distribution with a sharp roll-oX, knowing that a simple power law extrapolation would not connect the two groups. Although this function appears convincing, a large gap is left between the most intense GLEs and the weakest Miyake events. This vacancy is thought to represent the region in which ‘intermediate- sized’events, currently missing from the observational record, should be positioned. One means of finding such events might be to measure the historical radiocarbon record at ever higher precision. By applying this approach to Japanese asunaro tree rings, Miyahara et al. (2022) claim to have identified three such intermediate-sized events in the 13th century CE. In this study, we attempt to replicate these findings by making similarly high precision measurements on European oak over exactly the same calendar years.

Usoskin, I. G. and Kovaltsov, G. A. 2021. Mind the gap: new precise 14C data indicate the nature of extreme solar particle events. Geophysical Research Letters 48: e2021GL094848. https://doi.org/10.1029/2021GL094848

Miyahara, H., Tokanai, F., Moriya, T., Takeyama, M., Sakurai, H., Ohyama, M., Kazuho, H., and Hideyuki H. 2022. Recurrent large-scale solar proton events before the onset of the Wolf grand solar minimum. Geophysical Research Letters 49: 2021GL097201. https://doi.org/10.1029/2021GL097201

Speaker: Michael W. Dee (Centre for Isotope Research, ESRIG, University of Groningen, Groningen 9747 AG, the Netherlands)

12:13 P14 - Magnetospheric Response to Non-Dipolar Fields During Geomagnetic Excursions and Reversals (GERs)

Understanding how Earth’s magnetosphere responds to large-scale variations in the geomagnetic field is essential for constraining long-term space climate and radiation exposure. While the present-day magnetosphere is well characterized under a dipole-dominated field, its configuration during geomagnetic excursions and reversals (GER) remains poorly understood. We investigate solar wind-magnetosphere interaction under weakened and non-dipolar field conditions using global magnetohydrodynamic (MHD) simulation models. Paleomagnetic field configurations are used to represent excursion-like scenarios with reduced dipole strength and enhanced multipolar contributions. It is observed that under such conditions, magnetosphere becomes significantly
asymmetric and can get strongly compressed. The loss of dipole dominance results in more spatially distributed magnetic reconnection, increasing solar wind energy coupling and driving enhanced variability in magnetospheric dynamics. These structural changes imply reduced shielding efficiency and increased access of energetic particles to near-Earth space, with potential impacts on the radiation environment. This study provides a systematic framework for quantifying magnetospheric response under extreme geomagnetic conditions, improving our understanding of
space climate variability over geological timescales.

Speaker: Dr Shipra Sinha (Oulu U., FI)

12:14 P15 - Measuring the local Geomagnetic Disturbances in the INAF-Turin Astrophysical Observatory: two years of data around the solar maximum

In the context of the study of the conditions of the Earth's magnetosphere and space weather, we present the magnetometer installed at the INAF-Turin Astrophysical Observatory (Italy), included in the SWELTO (Space Weather Laboratory of Turin) project. A fluxgate magnetometer, after testing and calibration, has been positioned in the Turin Observatory (45°02'27"N, 7°45'48"E), and in November 2024 started to acquire data which can be viewed in quasi realtime on the SWELTO portal (https://swelto.oato.inaf.it/geomag_oato.html). The acquired data, in the form of voltage measurements, are converted and then calibrated by subtracting the quiet reference curve based on the quietest days of the month preceding the one being analyzed. This allows for an accurate identification and analysis of major geomagnetic disturbances. The instrument provides not only the three components of the Earth Magnetic Field, but also the local value of the so-called "Dst-index", that is compared to the global "Dst-index" provided by the World Data Center for Geomagnetism - Kyoto, finding a very good agreement for all the observed events. Here we summarize the calibration and the analysis of almost two years of magnetometer data (from end of 2024 to mid 2026), with a focus on known events that occurred during this period of Solar Maximum.

Speaker: Giorgio Bergamin (Turin U., IT)

12:15 P16 - On the time lag of GCRs and solar activity proxies

Investigating the relationship between galactic cosmic rays (GCRs) and solar activity is fundamental for understanding the physical mechanisms that govern particle transport in the heliosphere. Using multi-channel GCR flux data and solar activity proxies, previous studies have employed cross-correlation techniques, wavelet-coherence analyses, and information-theory- based methods, often framed within the force-field approximation to interpret the rigidity dependence of the modulation. Given the intrinsic non-linearity and non-stationarity of the data, we adopt a non-parametric approach based on Empirical Mode Decomposition to first sepa rate each time series into its intrinsic components. By identifying the modes that correspond to the shared space-climate dynamics between both signals, we compute their phase differ ence through Hilbert spectral analysis, leading to the determination of the time lag. Using a comprehensive multi-instrument and multi-species dataset, we determine the time lag be tween cosmic-ray intensities and several solar activity proxies, and we compare these findings with those obtained from well-established analyses. Our results reveal the time variability and characteristic patterns of the GCR–solar-proxy lag and provide qualitative confirmation of its expected charge-sign dependence. They explicitly highlight the role of gradient and curvature drifts in shaping these time-dependent effects within the heliosphere. Overall, our results offer important constraints for next-generation predictive models of cosmic-ray fluxes based on so lar activity proxies and contribute to improving long-term radiation-risk assessments for future human space exploration.

Speaker: David Pelosi (Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, Italy and INFN - Sezione di Perugia, Italy)

12:16 P17 - SciBar Cosmic Ray Telescope at Sierra Negra Cosmic Rays Observatory, Mexico: Simulation results and current status

The Scibar Cosmic-Ray Telescope (SciCRT) is the most promising detector of the Sierra Negra Cosmic Rays Observatory (SN-CRO). At this location, being a target and a tracker of secondary cosmic rays (SCR), the SciCRT offers a high probability of observing solar energetic particles and lower energy galactic cosmic rays (LEGCR); also, it allows the identification of incoming particles by measuring their energy deposition. We performed a Geant4-based simulation of the energy deposited by SCR in the optimally running SciCRT components and calculated the associated detection efficiency at their current state.

Co-author list:
F. Monterde‑Andrade (1,6), L. X. González (1,2), J. F. Valdés‑Galicia (1), O. G. Morales‑Olivares (1), M. A. Sergeeva (2), J. Newton‑Bosch (1,13), E. Ortiz (3), A. Hurtado (1), R. Taylor (1), Y. Matsubara (4), T. Sako (5), Y. Itow (6), T. Kawabata (6), K. Munakata (7), C. Kato (7), Y. Hayashi (7), Y. Masuda (7), M. Matsumoto (7), H. Takamaru (8), S. Shibata (4), A. Oshima (4), T. Koi (?), H. Kojima (4), H. Tsuchiya (9), K. Watanabe (10), M. Kozai (11), Y. Nakamura (12)

(1) Instituto de Geofísica, Universidad Nacional Autónoma de México, 04510 Ciudad de México, Mexico
(2) LANCE/SCiESMEX, Instituto de Geofísica, Unidad Michoacán, Universidad Nacional Autónoma de México, 58190 Morelia, Michoacán, Mexico
(3) Escuela Nacional de Ciencias de la Tierra, Universidad Nacional Autónoma de México, 04510 Ciudad de México, Mexico
(4) Center for Muon Science and Technology, Chubu University, Matsumoto, Kasugai, Aichi 487‑8501, Japan
(5) Institute for Cosmic Ray Research, University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277‑8582, Japan
(6) Institute for Space‑Earth Environmental Research, Nagoya University, Chikusa, Nagoya, Aichi 464‑8601, Japan
(7) Faculty of Science, Shinshu University, Asahi, Matsumoto, Nagano 390‑8621, Japan
(8) College of Engineering, Chubu University, Matsumoto, Kasugai, Aichi 487‑8501, Japan
(9) Japan Atomic Energy Agency, Tokai, Naka‑gun, Ibaraki 319‑1184, Japan
(10) National Defense Academy of Japan, Hashirimizu, Yokosuka, Kanagawa 239‑8686, Japan
(11) Joint Support‑Center for Data Science Research, Research Organization of Information and Systems, Midori‑cho, Tachikawa, Tokyo 190‑0014, Japan
(12) Institute of High Energy Physics, Chinese Academy of Sciences, Yuquan Road, Shijingshan District, Beijing 100049, China
(13) Programa Espacial Universitario, Coordinación de la Investigación Científica, Universidad Nacional Autónoma de México, 04510 Ciudad de México, Mexico

Speaker: Fernando Monterde-Andrade (Instituto de Geofísica, Universidad Nacional Autónoma de México, 04510 Ciudad de México, Mexico and Institute for Space-Earth Environmental Research, Nagoya University, Chikusa, Nagoya, Aichi 464-8601, Japan)

12:17 P18 - Detection of the 20 January 2026 Forbush Decrease by the Tanca Water-Cherenkov Detector

This study reports the detection of a major Forbush Decrease recorded on 20 January 2026 by the Tanca detector. Tanca is a ground-level water-Cherenkov detector located at the University of Campinas and operates as part of the Latin American Giant Observatory. The instrument consists of a polyethylene cylinder containing 11,400 litres of ultra-pure water, equipped with three photomultiplier tubes that record Cherenkov radiation produced by secondary cosmic-ray particles—primarily muons and electromagnetic components. The detector is installed on the university campus in Campinas (latitude 22.82° S, longitude 47.07° W, altitude 650 m above sea level), within the region of the South Atlantic Magnetic Anomaly, where the Earth's magnetic field intensity is significantly reduced. Following a fast Interplanetary Coronal Mass Ejection that triggered a severe G4-class geomagnetic storm, Tanca recorded a peak suppression of 8.88% in the galactic cosmic-ray flux relative to the pre-shock baseline. The decrease was driven by the ICME’s sheath region and magnetic cloud, which efficiently scattered and excluded galactic cosmic rays from the near-Earth environment. The results were compared with data from the Global Neutron Monitor Network. Although both detector types clearly registered the FD, the suppression observed by Tanca was smaller in magnitude than that measured by neutron monitors (NMs). This discrepancy is fundamentally explained by the different energy responses of the two detection techniques: whereas NMs are primarily sensitive to the hadronic component at lower effective primary energies, Tanca’s response is dominated by the muonic component. Consequently, Tanca’s effective primary energy threshold lies in the 30–40 GeV range, higher than that of NMs at comparable geomagnetic cut-off rigidities. These findings highlight the distinctive role of water-Cherenkov detectors in providing complementary observations, thereby broadening the energy coverage of ground-based cosmic-ray monitoring networks.

Speaker: Anderson Campos Fauth (University of Campinas-UNICAMP, Brazil)

12:18 P19 - Modelling of the diurnal variation of cosmic rays

Galactic cosmic rays (GCRs) exhibit a small anisotropy around Earth, which presents as diurnal variation (DV) in the count rates of ground-based neutron monitors (NMs). This fluctuation has a typical amplitude of around 0.3 %. Although the properties of DV have been extensively studied, previous literature still lacks a generalized DV model. Such a model could be used, for example, to separate DV from other fluctuations or to incorporate it into models of cosmic ray variability. In this work, as part of my Master's thesis research,present the first steps towards empirically modelling DV using 1-hour measurement data from the Oulu NM. Five different DV models were derived using several approaches including Fourier transform, wavelet transform and superposed epoch analysis. The validity of the models was tested by subtracting them from the NM data and examining their effect on the diurnal signal in the multitaper power spectrum, as well as on the shape of the average DV derived using superposed epoch analysis. The NM count rate data was also examined after model subtraction during both high-amplitude and low-amplitude DV periods. The testing showed that the wavelet transform provides a useful indicator for the amplitude of DV across different time periods. For simpler applications, Fourier transform and inverse Fourier transform may provide a straightforward way to extract the DV signal from measurements. From Oulu NM data, I also investigated the properties of DV after Forbush decreases (FDs), ground-level enhancements (GLEs) and during different solar magnetic polarity. DV shifts by 2-3 hours to earlier hours after FDs in agreement with previous literature, although no amplitude change was observed. Following GLEs, a possible and interesting shift of about 1 hour to later times was observed. During periods of negative solar magnetic field polarity, the maximum of DV is seen about 1-2 hours later than during positive polarity, also consistent with earlier findings.

Speaker: Mr Markus Similä (Oulu U., FI)

12:19 P20 - Effective Dose Rates at Aviation Altitudes During GLE#76 (21 November 2024)

High-energy solar particles entering the Earth’s atmosphere can significantly increase radiation exposure at flight altitudes, especially during Ground Level Enhancement (GLE) events. The aim of this work is to investigate aviation radiation exposure during the GLE#76 event on 21 November 2024, with a focus on estimating effective dose at aviation altitude. During the calculations, the background contribution of galactic cosmic rays (GCR) and the excess component of solar energetic particles (SEP) associated with the event were treated separately, and the total dose rate was then determined from their sum. The model was based on effective dose yield functions for protons and alpha particles, while the integration of the energy spectra was performed using the log-log method over the range corresponding to flight altitudes. As a first step of the validation, we reconstructed the GCR background dose. We then investigated the additional radiation exposure during the event by adding the GLE#76 SEP component at different altitudes and geomagnetic cutoff rigidities. The results show that the total effective dose rate during GLE#76 in the aviation altitude range could have significantly exceeded the quiet GCR background level, especially at high altitudes and in regions with low cutoff rigidity. Among the investigated flight altitudes, the highest total effective dose rate was obtained at the highest considered altitude, 50 kft, in a polar region, where it reached 16 μSv/h, while the corresponding background GCR component was about 10 μSv/h. In addition, we also computed the event integrated dose, which allows one to estimate the received exposure to radiation under different scenarios, that is, flight routes. The presented method is suitable for rapid estimation of aviation radiation exposure during solar energetic particle events and may contribute to an accurate assessment of the aviation risk associated with space weather events.

Speaker: Mr Bertalan Csapo (Oulu U., FI)

12:20 P21 - Sensitivity of polar neutron monitors to solar energetic particles

When solar energetic particle (SEP) events are observed at the ground by at least two sea- level neutron monitors (NMs) at different locations, they are called Ground Level Enhancements (GLEs). Very rarely, SEP-associated increases are observed exclusively at polar high-altitude NMs, which are the most sensitive NMs on Earth due to their reduced geomagnetic and atmospheric shielding. These events are called sub-GLEs. For this reason, sub-GLEs impose a sensitivity threshold on the NM network to SEP events, as they are characterized by increases that are not seen by any other NM at the ground. In this work, we employ the most recent NM yield function (Mishev et al., 2020) to quantitatively estimate the sensitivity of high-altitude (atmospheric depth ≈ 650 g/cm2) and sea-level (1033 g/cm2) polar NMs to SEPs. The sensitivity is defined as the minimum particle fluence above a given energy needed to observe a statistically significant increase in the NM count-rate. We denote this minimum observable fluence as the fluence threshold $F_{thres}$ (> $E_{eff}$) and refer to the corresponding reference energy as the effective energy $E_{eff}$.

Mishev, A. L., Koldobskiy, S. A., Kovaltsov, G. A., Gil, A., & Usoskin, I. G. (2020). Updated neutron‐monitor yield function: Bridging between in situ and ground‐based cosmic ray measurements. Journal of Geophysical Research: Space Physics, 125(2), e2019JA027433.

Speaker: Oscar Batalla (Department of Physics, University of Turin, Italy)

12:21 P22 - CME-driven sheath regions and interaction interfaces driving strong magnetospheric activity

Coronal mass ejections (CMEs) are the primary drivers of the strongest magnetospheric disturbances at Earth and other planets. The driving ejecta, often exhibiting flux rope signatures, carries the most sustained and intense magnetic fields. However, the sheath preceding a fast CME can also drive major disturbances, particularly at higher altitudes and in the radiation environment, due to its high density, strong magnetic fields, and large-amplitude fluctuations. Interacting CMEs create interfaces that exhibit geoeffective solar wind properties. Here, we present an analysis of the formation, properties, and geoeffects of the sheaths and interaction interfaces resulting from the merging of three prominent CMEs in November 2025. The event was observed by multiple, widely separated spacecraft in the inner heliosphere— BepiColombo, L1 spacecraft, Solar Orbiter, and STEREO-A, allowing us to probe the spatial variations and radial evolution of the structures. While the three CMEs remained separate at 0.32 au, they had merged into a complex structure by 1 au. The resulting sheaths and interaction interfaces strongly disturbed near-Earth space, producing significant effects including enhanced ionospheric currents and geomagnetically induced currents.

Co-author list:
Lina Hadid (2), Kazumasa Iwai (3), Rumi Nakamura (4), Mathias Rojo (5), Marco Pinto (6), Beatriz Sanchez‑Cano (7), Daniel Schmid (4), Daikou Shiota (8), Sae Aizawa (2), Shota Chiba (3), Daniel Heyner (10), Gaku Kinoshita (11), Yoshi Miyoshi (3), Go Murakami (12), Ken Matsui (3), Hao Sato (3), Laura Rodriguez Gracia (13), Rami Vainio (14), Anita Aikio (15), Matti Ala‑Lahti (1), Liisa Juusola (16), Kirsi Kauristie (16), Ari Viljanen (16), Heikki Vanhamäki (15), Lars Klingenstein (10), Adrian Poeppelwerth (10)

(1) University of Helsinki, Finland
(2) Laboratoire de Physique des Plasmas, CNRS, CEDEX Palaiseau, France
(3) ISEE, Division for Heliospheric Research, Nagoya University, Nagoya, Japan
(4) Space Research Institute, Austrian Academy of Sciences (ÖAW), Graz, Austria
(5) Institut de Recherche en Astrophysique et Planétologie (IRAP), CNRS – CNES – Université Toulouse III, Toulouse, France
(6) Laboratório de Instrumentação e Física Experimental de Partículas (LIP), Lisbon, Portugal
(7) University of Leicester, Leicester, United Kingdom
(8) National Institute of Information and Communications Technology, Koganei, Tokyo, Japan
(10) Technische Universität Braunschweig, Braunschweig, Germany
(11) University of Tokyo, Japan
(12) Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA), Japan
(13) Universidad de Alcalá, Madrid, Spain
(14) University of Turku, Finland
(15) University of Oulu, Finland
(16) Finnish Meteorological Institute, Finland

Speaker: Emilia Kilpua (University of Helsinki, Finland)

12:22 P23 - The EPOS data platform: Geomagnetic and electromagnetic data for a multi-disciplinary research

In this presentation we want to update on the progress made since the release of the EPOS data portal in 2023.
Research in the geomagnetic and electromagnetic geophysics community have long benefitted from open international exchange of knowledge. Open access to data, models and codes has become increasingly important in a landscape of multi-disciplinary research questions to support societal development. Many countries have developed national research infrastructure, but the need for transnational collaboration requires special effort and innovative approaches.
EPOS, the European Plate Observing System, is a multidisciplinary, distributed research infrastructure that facilitates the integrated use of data, data products, and facilities from the solid Earth science community in Europe. Through EPOS, geomagnetic and electromagnetic data, data products and models are made freely accessible to a wide range of audiences, covering education, stakeholder interests and engagement with policy makers.
While standards and exchange platforms for geomagnetic data and models have long been supported by IAGA committees, the access to magnetotelluric data has until recently been often restricted by missing data standards, repositories and open access policies. Within the EPOS framework, a data- sharing service for MT data has now been developed.
Members of the geomagnetic and EM community in Europe work towards the realisation of not only the data access, but also the delivery of tools and training material to make geo-electromagnetic data usable, following the FAIR principles.
Python based jupyter notebooks are provided by the TCS geomagnetism in order to teach the use of data sources provided by EPOS. The notebook for space weather related analysis shows some simple examples on how to combine data from different sources into joined data structures and diagrams.
This presentation aims to further engage the scientific community on what future developments are required and desirable to engage wider audiences with our science, data and vision.
The depicted example highlights the combination of three data sources, the comparision of local geomagnetic observatory data with global activity indices and (global) event detection information like sudden storm commencements. Such quick data access provides valuable information i.e for validating local event detectors and indices against global, IAGA endorsed standards.

Co-author list:
Maxim Yu. Smirnov (1), Juliane Hübert (2), Roman Leonhardt (3), Aude Chambodut (4), Oli Chambers (2), Juan José Curto (5), Santiago Marsal (5),Vincent Lesur (6), Jürgen Matzka (7), Anne Neska (8), Oliver Ritter (9), Ari Viljanen (10), Petya Trifonova (11)
1 Luleå University of Technology, Geosciences and Environmental Engineering, Luleå, Sweden.
2 British Geological Survey, The Lyell Centre, Edinburgh, United Kingdom.
3 Geosphere Austria, Conrad Observatory, Vienna, Austria.
4 University of Strasbourg, CNRS, Ecole et Observatoire des Science de la Terre (EOST), Strasbourg, France.
5 Observatori de l’Ebre, CSIC - University Ramon Llull, Roquetes, Spain.
6 Université de Paris, Institut de physique du globe de Paris (IPGP), Paris, France.
7 GFZ Helmholtz Centre for Geosciences, Geomagnetism, Niemegk, Germany.
8 Institute of Geophysics Polish Academy of Sciences, Geoelectromagnetism, Warszawa, Poland.
9 GFZ Helmholtz Centre for Geosciences, Geophysical Imaging, Potsdam, Germany.
10 FMI, Finnish Meteorological Institute, Helsinki, Finland.
11 National Institute of Geophysics- Geodesy and Geography - Bulgarian Academy of Science, Geomagnetism, Sofia, Bulgaria.

Speaker: Juan José Curto Subirats (Observatori de l’Ebre, ES)

12:23 P24 - Assessing Deep Learning Architectures for Space-Weather-Induced Atmospheric Correction in Urban Remote Sensing

As modern urban studies leverage high-cadence Earth Observation (EO) data for Smart Cities applications, the radiometric consistency of satellite imagery becomes a critical factor for automated analysis. However, solar activity cycles and long-term space climate variability significantly affect the ionosphere and upper atmosphere. These fluctuations introduce noise and geometric distortions into the datasets, which can degrade the precision of urban monitoring systems.
In the framework of my research internship at the German Aerospace Center (DLR) focused on Smart Cities, this study explores how Deep Learning could help mitigate these atmospheric effects. The focus is on investigating the potential integration of solar indices as auxiliary inputs for CNN or Transformer-based models. The goal is to see if a data-driven approach can improve automated correction in multi-temporal satellite series, particularly for urban footprint analysis. By connecting solar physics with remote sensing, this work aims to explore more reliable data processing methods for future smart cities infrastructures.

Speaker: Louis Foujols (ISAE-SUPAERO, Toulouse, France and German Aerospace Center (DLR), Earth Observation Center (EOC), Weßling, Germany)

12:24 P25 - A new composite of energetic electron precipitation and resulting atmospheric ionization based on combined POES and Proba-V data

The long observational record of POES satellites (1979 to present) is often used to estimate the EEP and study its long-term evolution and atmospheric impacts. The unique POES record has been the basis for the CMIP6 and CMIP7 versions of the EEP forcing recommended as an input to chemistry-climate models. While the POES measurements provide a long and nearly continuous data series they suffer, among other things, from poor energy resolution. They measure the energetic electrons with 3 integral channels spanning from >30 keV, >100 keV to >300 keV. There are strong indications that the relativistic part of the EEP spectrum, largely missed by the POES observations, is likely to be important because of the direct ionization it produces in the mesosphere. Typically, the high-energy part of the EEP spectrum is estimated by a power-law extrapolation from lower energies, but this might not be accurate. Here we present preliminary results combining the recently homogenized record of POES observations to another record of energetic electron measurements made at low-Earth orbit by the Proba-V satellite during 2013-present. Together these measurements cover energies from 30 keV to 8 MeV. We describe here the construction of the dataset and the methods used to join the Proba-V measured spectra to the spectra measured by POES, and finally evaluate the resulting atmospheric ionization.

Speaker: Jani Mantere (Oulu U., FI)

12:25 P26 - Validation of CMIP solar forcing input using EISCAT incoherent scatter radar, rockets and Arase satellite measurements

In polar latitudes, energetic electron precipitation (EEP; energies ~10s of keV to a few MeV) originating from the radiation belts and plasma sheet has a significant impact on the neutral composition and chemistry of the atmosphere in the mesosphere–lower thermosphere (∼60– 120 km) region. Precipitating electrons greatly disturb the atmospheric concentrations of odd nitrogen (NOx) and odd hydrogen (HOx) species, which in turn contribute to ozone depletion in the mesosphere and stratosphere. Despite its importance for atmospheric chemistry and vertical coupling processes, EEP is not accurately represented in solar forcing inputs used by Coupled Model Intercomparison Project (CMIP) climate models. In particular, uncertainties in EEP-driven ionization rates contribute to biases in the simulated atmospheric response.
This study presents a validation of EEP forcing in climate models at both local and global scales using ground based and satellite measurements. Local validation is performed by directly comparing modeled ionization rate (or electron density) profiles from Whole Atmosphere Community Climate Model (WACCM) with those derived from EISCAT-VHF incoherent scatter radar at Tromsø and rocket measurements carried out at Andøya and Esrange.
To study the EEP forcing at different longitudes, we use Arase satellite pitch angle–sorted electron flux data within the 0-10° pitch angle bin (encompassing both precipitating and trapped electron populations) and spanning energies from a few keV to ~1 MeV. The Arase energy–flux spectra obtained during EISCAT conjunction intervals are converted into (1) ionization rates and subsequently (2) electron density profiles using a forward modeling approach. The Arase energy-flux spectra are then scaled inorder to get the electron density profile that match best to the EISCAT observations during conjunction intervals. The derived energy dependent scaling factors are then applied to Arase measurements at similar L-shells, enabling the extension of EEP characterization across different longitudes.
Based on coordinated satellite and ground-based measurements, we address key questions related to EEP, including the quantification of EEP flux input into the Earth’s upper atmosphere and the characterization of its variability as a function of geomagnetic activity and magnetic local time.

Co-author list:
Antti Kero, Pekka Verronen, Yoshizumi Miyoshi, Joshua Fadiji, Shiang-Yu Wang, Yoichi Kazama, C-W. Jun, Satoshi Kasahara, Shoichiro Yokota, Kunihiro Keika, Tomoaki Hori, Takefumi Mitani, Takeshi Takashima, Ayako Matsuoka, Mariko Teramoto, Kazuhiro Yamamoto, Iku Shinohara

Speaker: Neethal Thomas (Oulu U., FI)

12:26 P27 - Assessing the climate system response to solar irradiance grand minima

Despite solar radiation being the primary external energy source driving the Earth’s climate system, the climatic impact of its long- term variations – such as prolonged periods of low solar activity called Grand Minima – still remains debatable due to the wide spread in solar irradiance reconstructions. Given the large implica- tions for detection and attribution studies, particularly to interprete past climate changes or to reduce the uncertainty in future climate projections, it is of great importance to disentangle the “direct” response to the solar signal from both natural and anthropogenic drivers and from the background “noise” represented by internal variability.
In this work we assess the response of the climate system to a solar grand minimum like the Maunder Minimum using the Isca intermediate-complexity General Circulation Model (GCM) from the University of Exeter, and possibly higher-complexity GCMs in the near future. We perform simulations with and without consis- tent ozone variations, thus isolating the contribution of the “top- down” stratospheric ozone-dynamic coupling from effects primarily driven by tropospheric dynamics. In this context, polar regions seem to play a key role as early or amplified indicators of solar-induced climatic changes.

Speaker: Lucaferri Lorenza (University of Rome Tor Vergata)

12:27 P28 - Relationship between solar activity and atmospheric circulation over Europe

There is growing evidence that solar variability associated with the 11-year sunspot cycle, particularly during solar minima and maxima, influences the troposphere. Numerous observational and modelling studies have linked the solar cycle to winter weather and climate variability in the Euro-Atlantic region. However, the strength of these links remains debated, owing to their reduced stability in extended records, inconsistent detectability across datasets and methodologies, and the seasonally dependent and time-lagged nature of the tropospheric response. Additional uncertainty arises from stratospheric processes, particularly the QBO and sudden stratospheric warmings, which can modulate solar signals through stratosphere– troposphere coupling.
This study investigates the relationship between solar variability and wintertime tropospheric circulation over central Europe by analysing the frequency of synoptic circulation types under different levels of solar activity during 1851–2022, using monthly mean sunspot numbers and the Groswetterlagen reanalysis classification of circulation types. By focusing on circulation- type frequencies, we provide a complementary view of the solar–circulation relationship and assess how solar activity influences tropospheric circulation at smaller temporal and spatial scales.
The results show a significant relationship between solar activity and tropospheric circulation; however, with clear differences between early and late winter. Under low solar activity, westerly types occur less frequently, indicating a suppression of zonal flow, in favour of a higher frequency of northerly types, particularly purely northerly ones. In contrast, under high solar activity, northerly types are significantly reduced, while westerly and south-westerly types are more frequent, predominantly in late winter. Anticyclonic situations occur more frequently under low solar activity, compensating for the reduced frequency of cyclonic types, predominantly in early winter. Finally, the circulation response is stronger during high- intensity solar cycles and weaker during low-intensity cycles.
In summary, solar variability modulates wintertime tropospheric circulation, with a clear subseasonal dependence: the response to low (high) solar activity is strongest in early (late) winter. The magnitude of the circulation response also varies with the amplitude of the solar cycle, and the contrast between early- and late-winter circulation patterns suggests a lagged tropospheric response to the solar signal.

Speaker: Hana Hanzlíková (Institute of Atmospheric Physics, Czech Academy of Sciences, Praha, Czechia)

12:28 P29 - Role of the Northern Polar Vortex and Geomagnetic Activity in Modulating Surface Solar Radiation and Solar Power Generation in Europe

In wintertime, the stratospheric polar vortex strongly influences European weather, affecting temperature, wind speed, and cloudiness. A strong polar vortex is typically associated with milder, windier, and cloudier conditions in northern Europe, while colder, calmer, and clearer weather prevails in southern Europe. Cloudiness directly controls the amount of solar radiation reaching the surface and therefore modulates solar power production.
One important factor influencing the polar vortex, and consequently surface weather, is energetic electron precipitation (EEP), for which the geomagnetic aa index can be used as a proxy. Enhanced EEP increases ozone loss in the upper atmosphere, leading to stratospheric cooling and a strengthened polar vortex. However, the influence of EEP on the polar vortex is strongest during the easterly phase of the quasi-biennial oscillation (QBO), which enhances planetary wave activity and meridional circulation transporting ozone toward polar regions. While the impacts of EEP on surface temperature and wind speed via the polar vortex have been investigated, its effects on cloud cover and surface incoming solar radiation remain largely unexplored.
In wintertime, countries in southern and central Europe receive sufficient solar radiation to produce a significant fraction of their electricity demand through solar power. In this study, we examine how winter cloud cover, surface incoming solar radiation, and solar power production respond to the strength of the polar vortex and geomagnetic activity across Europe. We find that stronger geomagnetic activity and stronger polar vortex in the easterly QBO phase are associated with reduced cloudiness and higher surface solar radiation in southern Europe, which enhances solar power production. For example, in Spain, the NAM index, which reflects the strength of the polar vortex, shows a correlation of 0.77 with solar power, while geomagnetic activity exhibits a correlation of 0.67. In both cases, the correlations are statistically highly significant.

Speaker: Veera Juntunen (University of Oulu, Finland)

12:29 Ionospheric irregularities in the polar regions - climatology and predictability

Instabilities and turbulence in the Earth ionosphere can lead to irregularities in the ionospheric plasma density. Ionospheric plasma irregularities are important space weather effects, which can significantly impact the propagation of radio waves through the upper atmosphere, and consequently degrade the quality of trans- ionospheric signals and communication with satellites. This can decrease the accuracy of positioning using the Global Navigation Satellite Systems (GNSS), such as GPS and Galileo, and can even lead to unavailability of such services. Therefore, a comprehensive understanding of ionospheric irregularities is vital for both research and operations that rely on satellite signals, and for the development of space weather forecasting services.
We present climatological studies of ionospheric irregularities in the polar regions carried out using the Swarm satellite data and ground-based measurements in the Arctic and in Antarctica. We discuss climatology of ionospheric irregularities in relation to the solar activity. With long term statistical studies, we show that the polar ionosphere in the Antarctic is in general more irregular than the Arctic. We also show how we employ ground- based data to develop an empirical model based on more than one solar cycle of the rate of change of the total electron content index (ROTI) maps, which now serves as a basis for regular services to forecast the level of ionospheric irregularities in the Arctic.
Finally, we present collaborative initiatives to advance our understanding on ionospheric plasma irregularities, as well as AGATA, which is the Scientific Research Programme of the Scientific Committee on Antarctic Research (SCAR). AGATA is a worldwide initiative that focuses on better understanding of coupling between and within atmospheric layers and geosphace in the Antarctic and also in the Arctic, and creates a platform for coordinated international efforts for comprehensive studies of the polar upper atmosphere.

Speaker: Wojciech J. Miloch (Department of Physics, University of Oslo, Oslo, Norway)

13:00 → 14:00 Lunch

Including water, salad, bread, butter and coffee/tea

14:00 → 15:31 1.2 Long-term evolution of the global structure of solar magnetic fields (chair Theo Chatzistergios)

Convener: Theodosios Chatzistergos (Max Planck Institute for Solar System Research, DE)

14:00 How Flux Emergence Shapes the Sun’s Large-scale Magnetic Field and Heliosphere

The magnetic activity of stars like the Sun is driven by the interplay of rotation and convection that fuels dynamo-action in their interiors. At the surface, dynamo-generated magnetic fields emerge as "spots" or active regions that influence the circumstellar environment via winds, radiation, and transient events like flares and coronal mass ejections (collectively “space weather”). Flux emergence often creates nested active regions whose persistence is central to the evolution of the Sun’s large-scale magnetic field. These regions can anchor the heliospheric current sheet and stall the reversal of the coronal magnetic field for several solar rotations. During the 11-year solar cycle, the distribution of solar wind sources undergoes a significant shift in response to the evolution of the large-scale magnetic field, transitioning from polar coronal holes at solar minima towards the active latitudes and equatorial coronal holes during maxima. This topological evolution modulates the mean rotation rate of the solar wind; rotation is slower during minima when sources are polar and faster (Carrington-like) during maxima when open field lines are anchored at lower latitudes. With ESA’s Solar Orbiter and NASA’s Parker Solar Probe exploring the inner heliosphere, the heliophysics community is building a global view of solar magnetism at both large and small scales. This talk highlights how the internal generation of magnetic field and its subsequent emergence to the surface collectively shape the heliosphere and the near-Earth space climate.

Speaker: Dr Adam Finley (ESA, NL)

14:20 Reconstructing the International Sunspot Number: progress and current status

The Sunspot Number series, with its almost 420 years of data, is one of the longest and most detailed available series in astrophysics, it is produced and maintained at the World Data Center SILSO (https://sidc.be/SILSO/home). Since 2010, eJorts have been undertaken by the solar community to revise both the Sunspot Number and the Group Number series (SN and GN). After an extensive recalibration in 2015, the historical series still suJers from various scale discrepancies which only a complete reconstruction will solve (Clette et al., 2016, 2023). I will present the latest news and plans for the near future.
Tests have been made on the techniques to reconstruct the Sunspot Number from 1814 to 1944 (Bhattacharya et al. 2023, 2024), while the historical data available has been sorted in a database and quality controlled (FARSUN, https://sidc.be/farsun). A summary of the available reconstruction techniques will be presented.
Progress of the SILSO part of the Belgian SUNRISE project will be presented. Launched in 2023, SUNRISE will modernize the day-to-day computation of the SN, and add the production, at the same frequency, of the GN (Belgian SUNRISE project).
In summary, in 2027, a historical database centralizing all available sunspot data (number of groups and spots when available) will be put into action, and will keep being updated as new data is digitized. During the same timeline, the production of the SN will be modernized and GN will be produced by the WDC-SILSO with the same frequency as SN. Combining the above historical and modern updates, new major versions of SN and GN will be released with complete transparency as to their construction.

Speaker: Dr Laure Lefevre (Royal Observatory of Belgium, BE)

14:40 Historical Measurements of Solar Magnetic fields

This work continues revisiting the manual observations of magnetic fields in sunspots from 1917-2025. Observations from Mount Wilson Observatory, Potsdam, and Crimean Astrophysical Observatory are included. We review the methods of observations, describe observational setups, compare measurements, and discuss systematics. While we see a solar cycle variation in the amplitude of strongest magnetic field, the results indicate no systematic change in sunspot field strength over the last 11 sunspot cycles.

Speaker: Dr Alexei Pevtsov (US National Solar Observatory, US)

14:52 Longitudinal Structuring of Solar Magnetic Activity from Cycle 23 to 25

We investigate the large-scale longitudinal and hemispheric organization of solar magnetic activity across multiple solar cycles, including Cycles 23, 24, and the ongoing Cycle 25. Using synoptic magnetic maps and flare catalogues, we examine the relationship between active longitudes, the spatial distribution of magnetically complex active regions, and the preferred longitudes of the most energetic solar flares.
Our analysis reveals that solar activity exhibits systematic hemispheric asymmetries that evolve with the solar cycle phase. Activity tends to dominate one hemisphere during the rising phase, often shifts around solar maximum, and may reorganize again during the declining phase. In addition, strong magnetic flux concentrations and major flares are not randomly distributed in longitude but cluster along persistent active longitudes that can remain stable for several Carrington rotations before undergoing abrupt longitudinal relocations of approximately 160°–180°. The evolution of these active longitudes displays quasi-periodic behavior on timescales of roughly 0.5–2 years, detectable in both magnetic and flare data.

Speaker: Dr Marianna Korsos (University of Sheffield, UK)

15:04 Phase analysis of solar-cycle reconstructions based upon 14C data

$^{14}$C measurements from tree rings have been used by Usoskin et al. (2021, 2025, 2026) to reconstruct past solar activity cycles over three millenia from the year 1000 BCE onward. In Weisshaar et al. (2023, A&A 671, A87) we analysed a first data set covering the epochs of reconstructed activity minima and maxima of the reconstructed cycles between 971 and 1900 CE in order to determine whether there is evidence that the cycle is synchronized (by some kind of external regular “clock”, such as planetary tides) or its phase (with respect to the mean period) drifts, i.e. performs a random walk. Using a method originally suggested by D. O. Gough we found clear evidence of random walk and excluded synchronization at a high level of statistical significance. A similar result was found when only considering the minima and maxima based on the record of monthly sunspot numbers since 1749.
We have now extended the analysis to the full set of reconstructed cycles covering three millennia and confirm the previous result, i.e. random phase migration and no evidence for synchronization. In addition to the Gough method, we have also applied an autocorrelation technique which, in principle, could detect a mixture of synchronization and migration. Again, we find pure phase migration and no synchronization.
We also show that criticism of our previous work by Stefani et al. (Solar Physics 298, 83; 2023) is unfounded.

Speaker: Prof. Eckhard Weisshaar (U. of Applied Sciences, Wiesbaden, DE)

15:19 Active regions and the large-scale magnetic field of solar cycle 24

We present a novel method for quantifying the eect that individual active regions have on the large-scale solar magnetic field as their magnetic flux spreads across the photosphere. This is achieved by combining the surface flux transport (SFT) model with a recent vector sum method.
We simulated the evolution of individual active regions of solar cycle 24 with the SFT model and used the vector sum to represent their state with a dipole vector at every Carrington rotation (CR). Due to the linearity, the sum of the resulting dipole vector time series is equivalent to the series calculated from the full SFT simulation. The dipole vector representation makes it straightforward to quantify the eect of each active region on the large-scale field (for example, using a dot product). Because the magnitude of the large-scale dipole vector closely follows the open solar flux (OSF) from the PFSS model, these eects also serve as a proxy for their OSF contributions.
Using these methods, we analyzed the rapid increase of the large-scale solar magnetic field in late 2014 that culminated in the OSF peak of solar cycle 24 in CR2157. We identified the most consequential active regions at the time of the OSF peak and found that 6 out of 7 of these regions emerged within a narrow longitude band in the southern hemisphere around Carrington longitude 240°. Some of these regions emerged already half a year prior to the peak OSF.
By randomizing the longitudinal locations of active regions in the SFT simulation, we find strong evidence that during the declining phase of the solar cycle 24 the longitudinal distribution of active regions was not random, but some of the active regions had a tendency to emerge at longitudes where their equatorial dipole components reinforced the existing large-scale field. Additionally, we found that taking into account the equatorial component of the solar dipole reduces the well-known degeneracy between the diusion and meridional flow amplitude parameters when optimizing the parameters of the SFT model based on the axisymmetric field alone. The reason is the opposite eect that diusion has on the axial and equatorial components of the solar magnetic field.
Our study demonstrates an eicient framework for studying the eects that the initially localized active region magnetic fields have on the global solar magnetic field as they spread across the photosphere. These methods are readily applicable for studying both the historical solar observations as well as the ongoing solar cycle 25.

Speaker: Dr Ismo Tähtinen (Oulu U., FI)

15:31 → 15:46 Group photo

15:46 → 16:08 Coffee break

16:08 → 16:38 Observing and Predicting Solar Cycle Variability

Observations of photospheric magnetic fields, active region emergence, and surface flows provide the primary constraints on predicting solar cycle variability. In particular, the strength of the polar fields during solar minimum remains a robust indicator of the amplitude of the subsequent cycle. However, reliable polar field measurements are only available for a few decades and key aspects of the solar cycle, such as hemispheric asymmetry, have only recently been examined in detail.
Ca II K observations and long-term sunspot records provide measures of the Sun’s magnetic field evolution prior to routine magnetograph measurements. Modern calibration methods and statistical approaches allow us to reconstruct aspects of the Sun’s large-scale magnetic field over multiple centuries. Variations in active region emergence patterns (such as timing and tilt) introduce uncertainty that fundamentally limit predictive capabilities. Differences in northern and southern hemispheric activity levels and reversal timings can lead to cross-equatorial flux transport and hemispheric coupling, with implications for the global heliospheric field.
In this talk, I will review what we have learned from observations of photospheric magnetism and how combining modern magnetograph observations with careful analysis of historical records spanning centuries continues to refine our understanding of solar cycle evolution and cycle-to-cycle variability. This provides indirect constraints on the Sun’s polar fields, offers valuable insight into secular variability, placing recent cycles in a longer-term context, and improves our ability to quantify sources of solar cycle variability. This is a critical next step to making more accurate predictions for the next cycle, as well as long-term changes in the heliospheric and space climate environment.

Speaker: Prof. Lisa Upton (Southwest Research Institute, US)

16:38 → 19:00 Poster session

16:38 P1 - Synchronisation Model of the Solar Dynamo

We present a solar dynamo model that appears capable of explaining various periodicities across a wide range of timescales in a self-consistent manner [1]. Starting with Rieger-type periodicities, we demonstrate that the two-planet spring tides of Venus, Earth, and Jupiter can excite magneto-Rossby waves in the solar tachocline. These waves have typical periods ranging from 100 to 300 days, and can reach amplitudes of metres per second or greater [2,3].
The first beat period, derived from the three tidally-excited waves, is 1.723 years. This aligns remarkably well with the observed period of the quasi-biennial oscillation (QBO) [1, 4]. The QBO could also help explain the astonishing regularity and calmness of the solar dynamo, a long-standing mystery.
The second beat period of 11.07 years, which arises from these three waves, corresponds to the long-term mean value of the Schwabe cycle. We hypothesise that the axisymmetric component of the α-effect, caused by these waves, is strong enough to synchronise the entire solar dynamo via parametric resonance [5].
Finally, we demonstrate that another beat, occurring between the 22.14-year Hale cycle and the Sun's 19.86-year periodic motion around the solar system's barycentre, could account for the Suess-de Vries cycle, which has a period of 193 years. The resulting spectrum of this double-synchronised dynamo model is found to be in very good agreement with climate-related data obtained from varved sediments in the Lake Lisan region [3, 6].

References
[1] Stefani, F. et al., Solar Phys. 300, 110 2025.
[2] Horstmann, G.M. et al., Astrophys. J. 944, 48 (2023)
[3] Stefani, F. et al., Solar Phys. 299, 51 (2024)
[4] Stefani, F. et al., https://arxiv.org/abs/2602.11227 (2026)
[5] Klevs M. et al. Solar Phys. 298, 90 (2023)
[6] Prasad, S. et al., Geology 32, 581 (2004)

Speaker: Frank Stefani (Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, D-01328 Dresden, Germany)

16:39 P2 - Inverting the Solar Meridional Circulation Profile in a Babcock-Leighton Flux Transport Dynamo Model through Genetic Modelling

The magnetohydrodynamic dynamo effect, which governs the interactions between internal solar fluid flows and magnetic fields, drives the Sun’s 11-year activity cycle. The meridional circulation, a key aspect of this process, plays a crucial role in regulating the solar cycle and its large-scale magnetic field, particularly within the framework of flux transport dynamo models. However, the deep internal profile of this large-scale flow remains challenging to observe, poorly constrained, and heavily debated.
In this work, we use the evolution of the Sun’s surface magnetic flux to constrain the internal profile of the meridional circulation. To achieve this, we developed a highly flexible basis of nearly orthogonal functions constructed from Legendre and Chebyshev polynomials to describe the latitu- dinal and radial dependencies of the flow, enabling the generation of complex circulation geometries. By combining these functions with weights optimized via a genetic algorithm, this versatile frame- work can adequately reproduce most kinematic profiles used in existing dynamo models, as well as more complex multicellular flow patterns, including, for example, small secondary flow cells located in depth and/or latitude.
Building on this mathematical foundation, we formulate an inversion problem to map the inter- nal meridional flow in a Babcock-Leighton flux transport dynamo model. Using a robust genetic algorithm, the flow is inverted by constraining the time-latitude structure of the deep toroidal mag- netic field to fit the shape of the observed surface butterfly diagram, and the surface magnetograms produced by our model to fit observed surface magnetic data.
This optimization process explores a complex, multimodal parameter space to identify not merely a single optimal parameter set, but rather a remarkably diverse population of statistically acceptable meridional circulation profiles. Notably, this ensemble includes complex, multiple-cell circulation patterns. Despite their internal topological differences, all accepted profiles successfully reproduce the fundamental characteristics of solar magnetism and match observed surface data. These results highlight the intrinsic degeneracy in inferring deep solar flows from surface magnetic evolution. Consequences for dynamo-based solar cycle prediction schemes will be briefly discussed.

Speaker: Laurie Lamy-Proulx (Université de Montréal, Montréal, Canada)

16:40 P3 - Exploring the Dominant Process of Solar Toroidal Magnetic Flux Loss

As the solar magnetic cycle evolves, subsurface toroidal magnetic flux is systematically generated and lost, and this work aims to identify the dominant process behind the flux loss. By employing a data-driven dynamo model and holding surface magnetic flux transport identical across the cycles 12-21, we conducted numerical experiments to isolate and assess the loss of subsurface toroidal flux, and then compared the results with two observational constraints: the butterfly diagram and the observed correlation between the polar field at cycle minimum and the strength of the next cycle. We found that under weak bulk diffusivity, the loss of the previous cycle's toroidal flux is dominated by cancellation with newly generated flux, causing the new cycle's actual flux to differ from its generated value and thereby preventing the simulation of the observed polar field-cycle strength correlation. When diffusivity is increased to a level where it dominates flux loss, residual flux is more effectively removed, restoring the polar field cycle strength correlation, yet operating in the diffusion-dominated regime suppresses the formation of the butterfly diagram. In contrast, active region emergence acts as an efficient mechanism for removing residual flux, and when it dominates the flux loss, both the correlation and the butterfly diagram are successfully reproduced. Thus, we conclude that active region emergence dominates the subsurface toroidal flux loss.

Speaker: Zebin Zhang (Institute of Frontier and Interdisciplinary Science and Institute of Space Sciences, Shandong University, People's Republic of China)

16:41 P4 - Stellar flares and starspots in TESS light curves

Stellar magnetic activity causes different observable phenomena on a stellar surface from dark spots to bright and explosive events, such as flares and coronal mass ejections. Both flares and starspots induce variations in stellar brightness, which can be seen in light curves. Starspots and stellar rotation together produce periodic dimmings of a star, whereas flares cause sudden and irregular brightenings as they release magnetic energy into a stellar atmosphere. Flares can have significant influence on planetary environments and consequently on the habitability of planets. The presented research focuses on late-type stars (spectral types F, G, K, and M), which have convective envelopes and are therefore expected to be magnetically active. We examine flares from seven late-type stars and assess their possible connection to starspots. Data from the Transiting Exoplanet Survey Satellite (TESS) are used in the analysis. Flares are identified from light curves using a flare detection program based on a machine learning algorithm. The timings of flares are compared to the stellar brightness trend in order to reveal a possible correlation between the flare occurrence and the stellar rotational phase.

Speaker: Emilia Rintamäki (Department of Physics, University of Helsinki)

16:42 P5 - Properties of Circumfacular regions derived from Hα and Ca II K synoptic observations

Circumfacular regions are dark structures surrounding active regions that appear in chromospheric observations, yet their physical properties and role in solar variability remain poorly constrained. Using ChroTel synoptic observations in Hα and Ca II K spanning the maximum of solar cycle 24 to the onset of cycle 25, we derive the photometric and geometric properties of circumfacular regions and compare them with plages, sunspots, and filaments. This study provides the most comprehensive characterization of circumfacular regions to date. We introduce a circumfacular photometric index and show that it is strongly correlated with established solar-activity proxies, with temporal variability primarily driven by changes in area coverage. The strength of these correlations evolves with the global activity level. We discuss the implications of these results for the interpretation of Balmer-line variability in the Sun and solar-like stars.

Speaker: Criscuoli Serena (NSO, US)

16:43 P6 - Total Solar Irradiance Variations Based on Fengyun3 Series Satellites

Solar irradiance observation is one of main objectives of Fengyun-3 (FY-3) series since the launch of first satellite FY-3A in 2008. For total solar irradiance (TSI), there are six satellites with the payload named Solar Irradiance Monitor (SIM) to perform operational observation. The performance of the instrument is gradually improving at the step of SIM-I, SIM-II and SIM-III. The SIM-III is scheduled for launch at the end of 2026. We recalibrate the early-stage data of SIM to build a dataset with the same scale and evaluate the TSI variations.

Speaker: Jin Qi (National Satellite Meteorological Center, China)

16:44 P7 - Quantifying the effect of passband on observations in the Ca ii K line

Solar irradiance is one of the key external forcing agents of Earth’s climate. Quantifying the effect of its variability requires knowledge of past irradiance changes over as long timescales as possible. Since direct space-based measurements are available for less than half a century, this necessitates irradiance reconstructions using models. On climate-relevant timescales, irradiance variability is driven by the evolution of the solar surface magnetic field. While most existing historical reconstructions are based on sunspot records, these provide limited information on the long-term evolution of bright magnetic features (faculae or plage), which is the main source of uncertainty in estimates of secular irradiance changes. Independent constraints on past solar magnetic activity are therefore essential.
One such proxy is the brightness of the Sun in the Ca II K spectral line. Full-disc Ca II K images have been taken since 1892 at multiple observatories worldwide, with individual archives covering different time intervals. Combining these data offers the potential to track changes in solar surface magnetism, and thus irradiance, over more than a century. However, this requires careful crosscalibration to account for differences in instruments and observational settings, in particular the varying spectral passbands used across and within archives.
To study the effect of different passbands on Ca II K observations, we use recent high spectral- and spatial-resolution data from the balloon-borne observatory Sunrise iii. By emulating different passbands of historical archives, we study how the observed Ca II K intensity depends on this choice. These results provide a basis for a cross-calibration of various historical Ca II K datasets and for improving constraints on long-term solar irradiance variability.

Co-author list:
Theodosios Chatzistergos (1), Natalie Krivova (1), Sami K. Solanki (1), Francisco A. Iglesias (1,2), Ilaria Ermolli (3), Andreas Lagg (1), Achim Gandorfer (1), Jose Carlos del Toro Iniesta (4,5), Yukio Katsukawa (6,7,8), Pietro Bernasconi (9), Thomas Berkefeld (10), Alex Feller (1), Tino L. Riethmüller (1), Alberto Álvarez-Herrero (11,5), Masahito Kubo (6), H. N. Smitha (1), David Orozco Suárez (4,5), Bianca Grauf (1), Michael Carpenter (9), Alexander Bell (10), Valentín Martínez Pillet (12,5), Laurent Gizon (1,13), Johannes Hoelken (1), Francisco Javier Bailén (4,5), Julian Blanco Rodríguez (14,5), Juan Sebastián Castellanos Durán (1), Edvarda Harnes (1), Ryohtaroh T. Ishikawa (15), Yusuke Kawabata (6), Takuma Matsumoto (16), Takayoshi Obal (7,1), Azaymi L. Siu‑Tapia (4,5), Hanna Strecker (4,5), Dušan Vukadinović (18,1), Yasuhito Narita (19,1)
1 Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
2 Grupo de Estudios en Heliofísica de Mendoza, CONICET, Universidad de Mendoza, 5500 Mendoza, Argentina
3 INAF Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone, Italy
4 Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
5 Spanish Space Solar Physics Consortium
6 National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
7 Department of Earth and Planetary Science. The University of Tokvo. Tokvo 113-0033, Japan
8 The Graduate University for Actae Se es (SOKENDAL), Mitaka, Tokyo 1818588, Japan
9 Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
10 Institut für Sonnenphysik (KIS), Georges-Köhler-Allee 401a, 79110 Freiburg, Germany
11 Instituto Nacional de Técnica Aeroespacial (INTA), E-28850 Torrejón de Ardoz, Spain
12 Instituto de Astrofísica de Canarias, Vía Láctea, s/n, E-38205 La Laguna, Spain
13 Institut für Astrophysik und Geophysik, Georg-August-Universität Göttingen, Germany
14 Universitat de Valencia Catedrático José Beltrán 2, E-46980 Paterna-Valencia, Spain
15 National Institute for Fusion Science, 322-6 Oroshi-cho, Toki City 509-5292, Japan
16 ISEE, Nagoya University, Furocho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan
17 Advanced Research Center for Space Science and Technology, Kanazawa University, Japan
18 Institut für Physik, Universität Graz, Universitätsplatz 5, 8010 Graz, Austria
19 Institut für Theoretische Physik, TU Braunschweig, 38106 Braunschweig, Germany

Speaker: Theodosios Chatzistergos (Max Planck Institute for Solar System Research, DE)

16:45 P8 - Sunspot Number V2.0 Through Solar Cycle 25: A Long-term Multi-Proxy Stability Analysis

The International Sunspot Number (SN V2.0) is one of the longest and most detailed available series in astrophysics and its accuracy and stability is important for a large variety of scientific domains, not the least of which is the evolution of the Earth Climate.
Since its recalibration and release in 2015, SN V2.0 has been the subject of sustained scrutiny within the scientific community yet no community-wide audit has covered the first full decade of that recalibration through the rise of Solar Cycle 25. A systematic assessment of the long-term stability of SN V2.0 is thus in order. In parallel, the American Sunspot Number, which has been computed continuously since the mid-20th century, experienced documented inconsistencies in the 1990s, as highlighted in previous studies (Schaefer, 1997). However, a comprehensive evaluation of its long-term behavior in the subsequent decades is still lacking.
In this work, we analyze the temporal stability of SN V2.0 over multi-decadal timescales. We compare SILSO SN V2.0 with AAVSO Ra, and independent proxies such as Sunspot areas, F10.7, Nobeyama microwave fluxes, Mg II, ISGI aa, and SDO/HMI unsigned field to diagnose the long-term behavior of both indices. We examine their mutual consistency, sensitivity to calibration changes, and suitability for long-term comparative studies. This analysis allows us to assess the relative robustness of each index, identify potential residual biases, and evaluate their reliability for studies of long-term solar variability. We conclude by discussing implications for future sunspot number reconstructions and by outlining perspectives for maintaining stable, homogeneous solar activity indices over extended timescales.

Speaker: Kalugodu Chandrashekhar (Royal Observatory of Belgium, Solar Influences Data analysis Center (SIDC), Brussels, Belgium)

16:46 P9 - THE AAVSO DAILY SUNSPOT DATABASE 1945-2026

For consistent measures of solar activity over many cycles, the only possibility is the long historical record of sunspot counts made by human eyes looking through a telescope. For this we have records going back four centuries, but there are substantial problems with consistent calibration across many cycles. An independent data source is the large number of sunspot counts collected by the American Association of Variable Star Observers (AAVSO) for 1945-- 2026. The problem is that all the raw data for before 2001 has been lost. Fortunately, back in 1996, I copied a large batch of the original raw counts, covering 1945 to the mid-1970s. Further, I have collected from a wide range of sources the original raw counts for many long- term AAVSO observers from 1945--2001. I now have daily raw counts, with coverage over every year 1945 to present, with ~20 long-term observers covering each year. With this database, my goal is to provide a consistent calibration of sunspot counts over the last eight cycles. However, I would like the suggestions and advice of SPACE CLIMATE 10 attendees on the best method to combine these counts into a consistent whole. I propose a method where the long-term observers that cover one cycle are normalized then averaged on a day-by-day basis, creating a consistent count over the cycle. Multiple cycles are linked to a common calibration by the long-term observers that cover two-or-more cycles. However, I need suggestions and improvements, as well as community acceptance of the method.

Speaker: Bradley E. Schaefer (Louisiana State University)

16:47 P10 - Sunspot drawings analysis with DigiSun and estimation of the uncertainty on group positions

Sunspot drawings are a unique source of information to study the long-term manifestation of the magnetic activity on the solar surface. The Royal Observatory of Belgium (ROB) started such drawings around 1940 and continues today on a daily basis, making the whole collection spanning over more than 80 years.
In this presentation, we discuss two important limitations to the full scientific exploitation of sunspot drawings: (1) the need for a fast and reliable software to analyse the drawings and (2) an estimation of the inherent uncertainty, in particular in position calculations. In order to overcome the first issue, the use of a standard analysis tool for the parameter measurement would make it easier to analyse contemporary sunspot drawings. In addition, it would help to fill the inevitable gaps from a single observation station by merging homogeneous data. Secondly, obtaining an appropriate estimate of the uncertainty would give us more comprehensive information and enable us to combine measurements from different drawing collections.
In the first part of the presentation, we describe DigiSun, a software developed by our team for measuring ROB sunspot drawings and for creating a catalog of sunspots. An important feature is the calculation of a pixel-wise true area, corrected for foreshortening. This calculation is more precise than most current software, which only considers one centroid position to correct foreshortening. Another strength of DigiSun is its ability to handle different drawing formats, which allows it to analyse drawings from other collections. It has been shared with other observatories such as the Specola Observatory in Locarno since 2019, Tapei and Kandili since 2024. In addition, DigiSun can be used to analyse historical drawings and extend the series of detailed solar parameters further back in time.
In the second part of the presentation, we aim to improve our understanding of the source of uncertainty present in sunspot drawings and provide a first global estimate of it. We estimate the uncertainties in heliographic coordinates, which is a crucial factor in the analysis of long-term solar differential rotation and the distribution of heliographic longitude and latitude across various solar cycles.

Speaker: Sabrina Bechet (ROB)

16:48 P11 - New high-resolution 10Be and 36Cl measurements across key Holocene intervals

Constraining the magnitude and occurrence of extreme solar energetic particle (SEP) events beyond the instrumental era remains central to space climate research and risk assessment. Cosmogenic radionuclides archived in polar ice cores, particularly beryllium-$^{10}$ ($^{10}$Be) and chlorine-$^{36}$ ($^{36}$Cl), provide one of the few direct observational windows into past solar activity. Here we present new high resolution $^{10}$Be and $^{36}$Cl measurements from Greenland and Antarctic ice cores spanning three intervals of particular interest: (i) the Carrington event (1859 CE), (ii) the recently identified radionuclide event at 7,208-year Before Present, and (iii) the post bomb period, which serves as a benchmark for atmospheric transport and depositional processes under well constrained conditions. Across the Carrington interval, we did not observe a significant enhancement in $^{36}$Cl concentrations. This result implies either that no exceptionally large SEP event occurred or that associated particles did not intersect Earth. In contrast, the 7,208-year BP interval is robustly confirmed in both nuclides, allowing us to assess its fluence spectrum and relative magnitude. Finally, the post bomb data reveal a clear 11-year cyclicity in $^{36}$Cl concentrations and good agreement with the $^{10}$Be records from both hemispheres. Together, these results place new observational constraints on the sensitivity and limits of ice core radionuclide proxies for reconstructing extreme solar activity.

Co-author list:
C. I. Paleari (1), R. Muscheler (2), M. Christl (3), A. Smith (4), C. Vockenhuber (3)
(1) Department of Physical Geography and Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
(2) Department of Earth and Environmental Sciences, Lund University, Lund, Sweden
(3) ETH Zürich, Laboratory of Ion Beam Physics, Zürich, Switzerland
(4) Centre for Accelerator Science, ANSTO, Lucas Heights, NSW, Australia

Speaker: Florian Mekhaldi (Stockholm U., SE)

16:49 P12 - Solar and Climatic Imprints in a 10Be Record from the NEEM Ice Core (Greenland) over 0–1650 CE

Cosmogenic 10Be records from ice cores are important proxies for reconstructing past solar activity. However, the incorporation of the isotope signal in ice is influenced by atmospheric transport and position processes, which can complicate the interpretation of the signal. Combining data from multiple sites may help reduce such noise and enhance the robustness of 10Be-based solar activity reconstructions. In this study, we present a new 10Be record from the North Greenland Eemian Ice Drilling (NEEM) ice core covering the period of 0–1650 CE. We find good agreement between the NEEM 10Be record and other ice core 10Be records from Greenland and Antarctica, and tree-ring 14C data, suggesting a common production signal. This finding is important for estimating and synchronizing solar imprints on the isotope production. However, incorporating the NEEM 10Be record into a stacked ice core 10Be dataset does not significantly improve its correlation with 14C. This indicates that site-specific influences may still affect the record and partially obscure the common production signal. In addition, potential climatic influences on the NEEM 10Be record are investigated by comparing it with chemical ion data from the same site. This approach can help better identification of local versus regional influences on the isotope record.

Speaker: Prof. Ala Aldahan (Department of Geosciences, United Arab Emirates University, Al Ain, United Arab Emirates)

16:50 P13 - Radiocarbon Measurements over the Proposed Solar Energetic Particle Events in the 13th Century CE

Several globally synchronous spikes in radiocarbon production have now been detected in known-age tree-ring archives. Such occurrences, commonly known a Miyake events, must have been prompted by enormous bursts of cosmic radiation. Extreme storms on the Sun are widely believed to be the ultimate source of this radiation. Indeed, the phenomena are expected to be akin to scaled-up versions of modern ground level enhancements (GLEs). Usoskin and Kovaltsov (2021) attempted to relate GLEs to Miyake events by way of a best-fit Weibull distribution with a sharp roll-oX, knowing that a simple power law extrapolation would not connect the two groups. Although this function appears convincing, a large gap is left between the most intense GLEs and the weakest Miyake events. This vacancy is thought to represent the region in which ‘intermediate- sized’events, currently missing from the observational record, should be positioned. One means of finding such events might be to measure the historical radiocarbon record at ever higher precision. By applying this approach to Japanese asunaro tree rings, Miyahara et al. (2022) claim to have identified three such intermediate-sized events in the 13th century CE. In this study, we attempt to replicate these findings by making similarly high precision measurements on European oak over exactly the same calendar years.

Usoskin, I. G. and Kovaltsov, G. A. 2021. Mind the gap: new precise 14C data indicate the nature of extreme solar particle events. Geophysical Research Letters 48: e2021GL094848. https://doi.org/10.1029/2021GL094848

Miyahara, H., Tokanai, F., Moriya, T., Takeyama, M., Sakurai, H., Ohyama, M., Kazuho, H., and Hideyuki H. 2022. Recurrent large-scale solar proton events before the onset of the Wolf grand solar minimum. Geophysical Research Letters 49: 2021GL097201. https://doi.org/10.1029/2021GL097201

Speaker: Michael W. Dee (Centre for Isotope Research, ESRIG, University of Groningen, Groningen 9747 AG, the Netherlands)

16:51 P14 - Magnetospheric Response to Non-Dipolar Fields During Geomagnetic Excursions and Reversals (GERs)

Understanding how Earth’s magnetosphere responds to large-scale variations in the geomagnetic field is essential for constraining long-term space climate and radiation exposure. While the present-day magnetosphere is well characterized under a dipole-dominated field, its configuration during geomagnetic excursions and reversals (GER) remains poorly understood. We investigate solar wind-magnetosphere interaction under weakened and non-dipolar field conditions using global magnetohydrodynamic (MHD) simulation models. Paleomagnetic field configurations are used to represent excursion-like scenarios with reduced dipole strength and enhanced multipolar contributions. It is observed that under such conditions, magnetosphere becomes significantly
asymmetric and can get strongly compressed. The loss of dipole dominance results in more spatially distributed magnetic reconnection, increasing solar wind energy coupling and driving enhanced variability in magnetospheric dynamics. These structural changes imply reduced shielding efficiency and increased access of energetic particles to near-Earth space, with potential impacts on the radiation environment. This study provides a systematic framework for quantifying magnetospheric response under extreme geomagnetic conditions, improving our understanding of
space climate variability over geological timescales.

Speaker: Dr Shipra Sinha (Oulu U., FI)

16:52 P15 - Measuring the local Geomagnetic Disturbances in the INAF-Turin Astrophysical Observatory: two years of data around the solar maximum

In the context of the study of the conditions of the Earth's magnetosphere and space weather, we present the magnetometer installed at the INAF-Turin Astrophysical Observatory (Italy), included in the SWELTO (Space Weather Laboratory of Turin) project. A fluxgate magnetometer, after testing and calibration, has been positioned in the Turin Observatory (45°02'27"N, 7°45'48"E), and in November 2024 started to acquire data which can be viewed in quasi realtime on the SWELTO portal (https://swelto.oato.inaf.it/geomag_oato.html). The acquired data, in the form of voltage measurements, are converted and then calibrated by subtracting the quiet reference curve based on the quietest days of the month preceding the one being analyzed. This allows for an accurate identification and analysis of major geomagnetic disturbances. The instrument provides not only the three components of the Earth Magnetic Field, but also the local value of the so-called "Dst-index", that is compared to the global "Dst-index" provided by the World Data Center for Geomagnetism - Kyoto, finding a very good agreement for all the observed events. Here we summarize the calibration and the analysis of almost two years of magnetometer data (from end of 2024 to mid 2026), with a focus on known events that occurred during this period of Solar Maximum.

Speaker: Giorgio Bergamin (INAF OATo)

16:54 P16 - On the time lag of GCRs and solar activity proxies

Investigating the relationship between galactic cosmic rays (GCRs) and solar activity is fundamental for understanding the physical mechanisms that govern particle transport in the heliosphere. Using multi-channel GCR flux data and solar activity proxies, previous studies have employed cross-correlation techniques, wavelet-coherence analyses, and information-theory- based methods, often framed within the force-field approximation to interpret the rigidity dependence of the modulation. Given the intrinsic non-linearity and non-stationarity of the data, we adopt a non-parametric approach based on Empirical Mode Decomposition to first sepa rate each time series into its intrinsic components. By identifying the modes that correspond to the shared space-climate dynamics between both signals, we compute their phase differ ence through Hilbert spectral analysis, leading to the determination of the time lag. Using a comprehensive multi-instrument and multi-species dataset, we determine the time lag be tween cosmic-ray intensities and several solar activity proxies, and we compare these findings with those obtained from well-established analyses. Our results reveal the time variability and characteristic patterns of the GCR–solar-proxy lag and provide qualitative confirmation of its expected charge-sign dependence. They explicitly highlight the role of gradient and curvature drifts in shaping these time-dependent effects within the heliosphere. Overall, our results offer important constraints for next-generation predictive models of cosmic-ray fluxes based on so lar activity proxies and contribute to improving long-term radiation-risk assessments for future human space exploration.

Speaker: David Pelosi (Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, Italy and INFN - Sezione di Perugia, Italy)

16:55 P17 - SciBar Cosmic Ray Telescope at Sierra Negra Cosmic Rays Observatory, Mexico: Simulation results and current status

The Scibar Cosmic-Ray Telescope (SciCRT) is the most promising detector of the Sierra Negra Cosmic Rays Observatory (SN-CRO). At this location, being a target and a tracker of secondary cosmic rays (SCR), the SciCRT offers a high probability of observing solar energetic particles and lower energy galactic cosmic rays (LEGCR); also, it allows the identification of incoming particles by measuring their energy deposition. We performed a Geant4-based simulation of the energy deposited by SCR in the optimally running SciCRT components and calculated the associated detection efficiency at their current state.

Co-author list:
F. Monterde‑Andrade (1,6), L. X. González (1,2), J. F. Valdés‑Galicia (1), O. G. Morales‑Olivares (1), M. A. Sergeeva (2), J. Newton‑Bosch (1,13), E. Ortiz (3), A. Hurtado (1), R. Taylor (1), Y. Matsubara (4), T. Sako (5), Y. Itow (6), T. Kawabata (6), K. Munakata (7), C. Kato (7), Y. Hayashi (7), Y. Masuda (7), M. Matsumoto (7), H. Takamaru (8), S. Shibata (4), A. Oshima (4), T. Koi (?), H. Kojima (4), H. Tsuchiya (9), K. Watanabe (10), M. Kozai (11), Y. Nakamura (12)

(1) Instituto de Geofísica, Universidad Nacional Autónoma de México, 04510 Ciudad de México, Mexico
(2) LANCE/SCiESMEX, Instituto de Geofísica, Unidad Michoacán, Universidad Nacional Autónoma de México, 58190 Morelia, Michoacán, Mexico
(3) Escuela Nacional de Ciencias de la Tierra, Universidad Nacional Autónoma de México, 04510 Ciudad de México, Mexico
(4) Center for Muon Science and Technology, Chubu University, Matsumoto, Kasugai, Aichi 487‑8501, Japan
(5) Institute for Cosmic Ray Research, University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277‑8582, Japan
(6) Institute for Space‑Earth Environmental Research, Nagoya University, Chikusa, Nagoya, Aichi 464‑8601, Japan
(7) Faculty of Science, Shinshu University, Asahi, Matsumoto, Nagano 390‑8621, Japan
(8) College of Engineering, Chubu University, Matsumoto, Kasugai, Aichi 487‑8501, Japan
(9) Japan Atomic Energy Agency, Tokai, Naka‑gun, Ibaraki 319‑1184, Japan
(10) National Defense Academy of Japan, Hashirimizu, Yokosuka, Kanagawa 239‑8686, Japan
(11) Joint Support‑Center for Data Science Research, Research Organization of Information and Systems, Midori‑cho, Tachikawa, Tokyo 190‑0014, Japan
(12) Institute of High Energy Physics, Chinese Academy of Sciences, Yuquan Road, Shijingshan District, Beijing 100049, China
(13) Programa Espacial Universitario, Coordinación de la Investigación Científica, Universidad Nacional Autónoma de México, 04510 Ciudad de México, Mexico

Speaker: Fernando Monterde-Andrade (Instituto de Geofísica, Universidad Nacional Autónoma de México, 04510 Ciudad de México, Mexico and Institute for Space-Earth Environmental Research, Nagoya University, Chikusa, Nagoya, Aichi 464-8601, Japan)

16:56 P18 - Detection of the 20 January 2026 Forbush Decrease by the Tanca Water-Cherenkov Detector

This study reports the detection of a major Forbush Decrease recorded on 20 January 2026 by the Tanca detector. Tanca is a ground-level water-Cherenkov detector located at the University of Campinas and operates as part of the Latin American Giant Observatory. The instrument consists of a polyethylene cylinder containing 11,400 litres of ultra-pure water, equipped with three photomultiplier tubes that record Cherenkov radiation produced by secondary cosmic-ray particles—primarily muons and electromagnetic components. The detector is installed on the university campus in Campinas (latitude 22.82° S, longitude 47.07° W, altitude 650 m above sea level), within the region of the South Atlantic Magnetic Anomaly, where the Earth's magnetic field intensity is significantly reduced. Following a fast Interplanetary Coronal Mass Ejection that triggered a severe G4-class geomagnetic storm, Tanca recorded a peak suppression of 8.88% in the galactic cosmic-ray flux relative to the pre-shock baseline. The decrease was driven by the ICME’s sheath region and magnetic cloud, which efficiently scattered and excluded galactic cosmic rays from the near-Earth environment. The results were compared with data from the Global Neutron Monitor Network. Although both detector types clearly registered the FD, the suppression observed by Tanca was smaller in magnitude than that measured by neutron monitors (NMs). This discrepancy is fundamentally explained by the different energy responses of the two detection techniques: whereas NMs are primarily sensitive to the hadronic component at lower effective primary energies, Tanca’s response is dominated by the muonic component. Consequently, Tanca’s effective primary energy threshold lies in the 30–40 GeV range, higher than that of NMs at comparable geomagnetic cut-off rigidities. These findings highlight the distinctive role of water-Cherenkov detectors in providing complementary observations, thereby broadening the energy coverage of ground-based cosmic-ray monitoring networks.

Speaker: Anderson Campos Fauth (University of Campinas-UNICAMP, Brazil)

16:57 P19 - Modelling of the diurnal variation of cosmic rays

Galactic cosmic rays (GCRs) exhibit a small anisotropy around Earth, which presents as diurnal variation (DV) in the count rates of ground-based neutron monitors (NMs). This fluctuation has a typical amplitude of around 0.3 %. Although the properties of DV have been extensively studied, previous literature still lacks a generalized DV model. Such a model could be used, for example, to separate DV from other fluctuations or to incorporate it into models of cosmic ray variability. In this work, as part of my Master's thesis research,present the first steps towards empirically modelling DV using 1-hour measurement data from the Oulu NM. Five different DV models were derived using several approaches including Fourier transform, wavelet transform and superposed epoch analysis. The validity of the models was tested by subtracting them from the NM data and examining their effect on the diurnal signal in the multitaper power spectrum, as well as on the shape of the average DV derived using superposed epoch analysis. The NM count rate data was also examined after model subtraction during both high-amplitude and low-amplitude DV periods. The testing showed that the wavelet transform provides a useful indicator for the amplitude of DV across different time periods. For simpler applications, Fourier transform and inverse Fourier transform may provide a straightforward way to extract the DV signal from measurements. From Oulu NM data, I also investigated the properties of DV after Forbush decreases (FDs), ground-level enhancements (GLEs) and during different solar magnetic polarity. DV shifts by 2-3 hours to earlier hours after FDs in agreement with previous literature, although no amplitude change was observed. Following GLEs, a possible and interesting shift of about 1 hour to later times was observed. During periods of negative solar magnetic field polarity, the maximum of DV is seen about 1-2 hours later than during positive polarity, also consistent with earlier findings.

Speaker: Mr Markus Similä (Oulu U., FI)

16:58 P20 - Effective Dose Rates at Aviation Altitudes During GLE#76 (21 November 2024)

High-energy solar particles entering the Earth’s atmosphere can significantly increase radiation exposure at flight altitudes, especially during Ground Level Enhancement (GLE) events. The aim of this work is to investigate aviation radiation exposure during the GLE#76 event on 21 November 2024, with a focus on estimating effective dose at aviation altitude. During the calculations, the background contribution of galactic cosmic rays (GCR) and the excess component of solar energetic particles (SEP) associated with the event were treated separately, and the total dose rate was then determined from their sum. The model was based on effective dose yield functions for protons and alpha particles, while the integration of the energy spectra was performed using the log-log method over the range corresponding to flight altitudes. As a first step of the validation, we reconstructed the GCR background dose. We then investigated the additional radiation exposure during the event by adding the GLE#76 SEP component at different altitudes and geomagnetic cutoff rigidities. The results show that the total effective dose rate during GLE#76 in the aviation altitude range could have significantly exceeded the quiet GCR background level, especially at high altitudes and in regions with low cutoff rigidity. Among the investigated flight altitudes, the highest total effective dose rate was obtained at the highest considered altitude, 50 kft, in a polar region, where it reached 16 μSv/h, while the corresponding background GCR component was about 10 μSv/h. In addition, we also computed the event integrated dose, which allows one to estimate the received exposure to radiation under different scenarios, that is, flight routes. The presented method is suitable for rapid estimation of aviation radiation exposure during solar energetic particle events and may contribute to an accurate assessment of the aviation risk associated with space weather events.

Speaker: Mr Bertalan Csapo (Oulu U., FI)

16:59 P21 - Sensitivity of polar neutron monitors to solar energetic particles

When solar energetic particle (SEP) events are observed at the ground by at least two sea- level neutron monitors (NMs) at different locations, they are called Ground Level Enhancements (GLEs). Very rarely, SEP-associated increases are observed exclusively at polar high-altitude NMs, which are the most sensitive NMs on Earth due to their reduced geomagnetic and atmospheric shielding. These events are called sub-GLEs. For this reason, sub-GLEs impose a sensitivity threshold on the NM network to SEP events, as they are characterized by increases that are not seen by any other NM at the ground. In this work, we employ the most recent NM yield function (Mishev et al., 2020) to quantitatively estimate the sensitivity of high-altitude (atmospheric depth ≈ 650 g/cm2) and sea-level (1033 g/cm2) polar NMs to SEPs. The sensitivity is defined as the minimum particle fluence above a given energy needed to observe a statistically significant increase in the NM count-rate. We denote this minimum observable fluence as the fluence threshold $F_{thres}$ (> $E_{eff}$) and refer to the corresponding reference energy as the effective energy $E_{eff}$.

Mishev, A. L., Koldobskiy, S. A., Kovaltsov, G. A., Gil, A., & Usoskin, I. G. (2020). Updated neutron‐monitor yield function: Bridging between in situ and ground‐based cosmic ray measurements. Journal of Geophysical Research: Space Physics, 125(2), e2019JA027433.

Speaker: Oscar Batalla (Department of Physics, University of Turin, Italy)

17:00 P22 - CME-driven sheath regions and interaction interfaces driving strong magnetospheric activity

Coronal mass ejections (CMEs) are the primary drivers of the strongest magnetospheric disturbances at Earth and other planets. The driving ejecta, often exhibiting flux rope signatures, carries the most sustained and intense magnetic fields. However, the sheath preceding a fast CME can also drive major disturbances, particularly at higher altitudes and in the radiation environment, due to its high density, strong magnetic fields, and large-amplitude fluctuations. Interacting CMEs create interfaces that exhibit geoeffective solar wind properties. Here, we present an analysis of the formation, properties, and geoeffects of the sheaths and interaction interfaces resulting from the merging of three prominent CMEs in November 2025. The event was observed by multiple, widely separated spacecraft in the inner heliosphere— BepiColombo, L1 spacecraft, Solar Orbiter, and STEREO-A, allowing us to probe the spatial variations and radial evolution of the structures. While the three CMEs remained separate at 0.32 au, they had merged into a complex structure by 1 au. The resulting sheaths and interaction interfaces strongly disturbed near-Earth space, producing significant effects including enhanced ionospheric currents and geomagnetically induced currents.

Co-author list:
Lina Hadid (2), Kazumasa Iwai (3), Rumi Nakamura (4), Mathias Rojo (5), Marco Pinto (6), Beatriz Sanchez‑Cano (7), Daniel Schmid (4), Daikou Shiota (8), Sae Aizawa (2), Shota Chiba (3), Daniel Heyner (10), Gaku Kinoshita (11), Yoshi Miyoshi (3), Go Murakami (12), Ken Matsui (3), Hao Sato (3), Laura Rodriguez Gracia (13), Rami Vainio (14), Anita Aikio (15), Matti Ala‑Lahti (1), Liisa Juusola (16), Kirsi Kauristie (16), Ari Viljanen (16), Heikki Vanhamäki (15), Lars Klingenstein (10), Adrian Poeppelwerth (10)

(1) University of Helsinki, Finland
(2) Laboratoire de Physique des Plasmas, CNRS, CEDEX Palaiseau, France
(3) ISEE, Division for Heliospheric Research, Nagoya University, Nagoya, Japan
(4) Space Research Institute, Austrian Academy of Sciences (ÖAW), Graz, Austria
(5) Institut de Recherche en Astrophysique et Planétologie (IRAP), CNRS – CNES – Université Toulouse III, Toulouse, France
(6) Laboratório de Instrumentação e Física Experimental de Partículas (LIP), Lisbon, Portugal
(7) University of Leicester, Leicester, United Kingdom
(8) National Institute of Information and Communications Technology, Koganei, Tokyo, Japan
(10) Technische Universität Braunschweig, Braunschweig, Germany
(11) University of Tokyo, Japan
(12) Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA), Japan
(13) Universidad de Alcalá, Madrid, Spain
(14) University of Turku, Finland
(15) University of Oulu, Finland
(16) Finnish Meteorological Institute, Finland

Speaker: Emilia Kilpua (University of Helsinki, Finland)

17:01 P23 - The EPOS data platform: Geomagnetic and electromagnetic data for a multi-disciplinary research

In this presentation we want to update on the progress made since the release of the EPOS data portal in 2023.
Research in the geomagnetic and electromagnetic geophysics community have long benefitted from open international exchange of knowledge. Open access to data, models and codes has become increasingly important in a landscape of multi-disciplinary research questions to support societal development. Many countries have developed national research infrastructure, but the need for transnational collaboration requires special effort and innovative approaches.
EPOS, the European Plate Observing System, is a multidisciplinary, distributed research infrastructure that facilitates the integrated use of data, data products, and facilities from the solid Earth science community in Europe. Through EPOS, geomagnetic and electromagnetic data, data products and models are made freely accessible to a wide range of audiences, covering education, stakeholder interests and engagement with policy makers.
While standards and exchange platforms for geomagnetic data and models have long been supported by IAGA committees, the access to magnetotelluric data has until recently been often restricted by missing data standards, repositories and open access policies. Within the EPOS framework, a data- sharing service for MT data has now been developed.
Members of the geomagnetic and EM community in Europe work towards the realisation of not only the data access, but also the delivery of tools and training material to make geo-electromagnetic data usable, following the FAIR principles.
Python based jupyter notebooks are provided by the TCS geomagnetism in order to teach the use of data sources provided by EPOS. The notebook for space weather related analysis shows some simple examples on how to combine data from different sources into joined data structures and diagrams.
This presentation aims to further engage the scientific community on what future developments are required and desirable to engage wider audiences with our science, data and vision.
The depicted example highlights the combination of three data sources, the comparision of local geomagnetic observatory data with global activity indices and (global) event detection information like sudden storm commencements. Such quick data access provides valuable information i.e for validating local event detectors and indices against global, IAGA endorsed standards.

Co-author list:
Maxim Yu. Smirnov (1), Juliane Hübert (2), Roman Leonhardt (3), Aude Chambodut (4), Oli Chambers (2), Juan José Curto (5), Santiago Marsal (5),Vincent Lesur (6), Jürgen Matzka (7), Anne Neska (8), Oliver Ritter (9), Ari Viljanen (10), Petya Trifonova (11)
1 Luleå University of Technology, Geosciences and Environmental Engineering, Luleå, Sweden.
2 British Geological Survey, The Lyell Centre, Edinburgh, United Kingdom.
3 Geosphere Austria, Conrad Observatory, Vienna, Austria.
4 University of Strasbourg, CNRS, Ecole et Observatoire des Science de la Terre (EOST), Strasbourg, France.
5 Observatori de l’Ebre, CSIC - University Ramon Llull, Roquetes, Spain.
6 Université de Paris, Institut de physique du globe de Paris (IPGP), Paris, France.
7 GFZ Helmholtz Centre for Geosciences, Geomagnetism, Niemegk, Germany.
8 Institute of Geophysics Polish Academy of Sciences, Geoelectromagnetism, Warszawa, Poland.
9 GFZ Helmholtz Centre for Geosciences, Geophysical Imaging, Potsdam, Germany.
10 FMI, Finnish Meteorological Institute, Helsinki, Finland.
11 National Institute of Geophysics- Geodesy and Geography - Bulgarian Academy of Science, Geomagnetism, Sofia, Bulgaria.

Speaker: Juan José Curto Subirats (Observatori de l’Ebre, ES)

17:02 P24 - Assessing Deep Learning Architectures for Space-Weather-Induced Atmospheric Correction in Urban Remote Sensing

As modern urban studies leverage high-cadence Earth Observation (EO) data for Smart Cities applications, the radiometric consistency of satellite imagery becomes a critical factor for automated analysis. However, solar activity cycles and long-term space climate variability significantly affect the ionosphere and upper atmosphere. These fluctuations introduce noise and geometric distortions into the datasets, which can degrade the precision of urban monitoring systems.
In the framework of my research internship at the German Aerospace Center (DLR) focused on Smart Cities, this study explores how Deep Learning could help mitigate these atmospheric effects. The focus is on investigating the potential integration of solar indices as auxiliary inputs for CNN or Transformer-based models. The goal is to see if a data-driven approach can improve automated correction in multi-temporal satellite series, particularly for urban footprint analysis. By connecting solar physics with remote sensing, this work aims to explore more reliable data processing methods for future smart cities infrastructures.

Speaker: Louis Foujols (ISAE-SUPAERO, Toulouse, France and German Aerospace Center (DLR), Earth Observation Center (EOC), Weßling, Germany)

17:03 P25 - A new composite of energetic electron precipitation and resulting atmospheric ionization based on combined POES and Proba-V data

The long observational record of POES satellites (1979 to present) is often used to estimate the EEP and study its long-term evolution and atmospheric impacts. The unique POES record has been the basis for the CMIP6 and CMIP7 versions of the EEP forcing recommended as an input to chemistry-climate models. While the POES measurements provide a long and nearly continuous data series they suffer, among other things, from poor energy resolution. They measure the energetic electrons with 3 integral channels spanning from >30 keV, >100 keV to >300 keV. There are strong indications that the relativistic part of the EEP spectrum, largely missed by the POES observations, is likely to be important because of the direct ionization it produces in the mesosphere. Typically, the high-energy part of the EEP spectrum is estimated by a power-law extrapolation from lower energies, but this might not be accurate. Here we present preliminary results combining the recently homogenized record of POES observations to another record of energetic electron measurements made at low-Earth orbit by the Proba-V satellite during 2013-present. Together these measurements cover energies from 30 keV to 8 MeV. We describe here the construction of the dataset and the methods used to join the Proba-V measured spectra to the spectra measured by POES, and finally evaluate the resulting atmospheric ionization.

Speaker: Jani Mantere (Oulu U., FI)

17:04 P26 - Validation of CMIP solar forcing input using EISCAT incoherent scatter radar, rockets and Arase satellite measurements

In polar latitudes, energetic electron precipitation (EEP; energies ~10s of keV to a few MeV) originating from the radiation belts and plasma sheet has a significant impact on the neutral composition and chemistry of the atmosphere in the mesosphere–lower thermosphere (∼60– 120 km) region. Precipitating electrons greatly disturb the atmospheric concentrations of odd nitrogen (NOx) and odd hydrogen (HOx) species, which in turn contribute to ozone depletion in the mesosphere and stratosphere. Despite its importance for atmospheric chemistry and vertical coupling processes, EEP is not accurately represented in solar forcing inputs used by Coupled Model Intercomparison Project (CMIP) climate models. In particular, uncertainties in EEP-driven ionization rates contribute to biases in the simulated atmospheric response.
This study presents a validation of EEP forcing in climate models at both local and global scales using ground based and satellite measurements. Local validation is performed by directly comparing modeled ionization rate (or electron density) profiles from Whole Atmosphere Community Climate Model (WACCM) with those derived from EISCAT-VHF incoherent scatter radar at Tromsø and rocket measurements carried out at Andøya and Esrange.
To study the EEP forcing at different longitudes, we use Arase satellite pitch angle–sorted electron flux data within the 0-10° pitch angle bin (encompassing both precipitating and trapped electron populations) and spanning energies from a few keV to ~1 MeV. The Arase energy–flux spectra obtained during EISCAT conjunction intervals are converted into (1) ionization rates and subsequently (2) electron density profiles using a forward modeling approach. The Arase energy-flux spectra are then scaled inorder to get the electron density profile that match best to the EISCAT observations during conjunction intervals. The derived energy dependent scaling factors are then applied to Arase measurements at similar L-shells, enabling the extension of EEP characterization across different longitudes.
Based on coordinated satellite and ground-based measurements, we address key questions related to EEP, including the quantification of EEP flux input into the Earth’s upper atmosphere and the characterization of its variability as a function of geomagnetic activity and magnetic local time.

Co-author list:
Antti Kero, Pekka Verronen, Yoshizumi Miyoshi, Joshua Fadiji, Shiang-Yu Wang, Yoichi Kazama, C-W. Jun, Satoshi Kasahara, Shoichiro Yokota, Kunihiro Keika, Tomoaki Hori, Takefumi Mitani, Takeshi Takashima, Ayako Matsuoka, Mariko Teramoto, Kazuhiro Yamamoto, Iku Shinohara

Speaker: Neethal Thomas (Oulu U., FI)

17:05 P27 - Assessing the climate system response to solar irradiance grand minima

Despite solar radiation being the primary external energy source driving the Earth’s climate system, the climatic impact of its long- term variations – such as prolonged periods of low solar activity called Grand Minima – still remains debatable due to the wide spread in solar irradiance reconstructions. Given the large implica- tions for detection and attribution studies, particularly to interprete past climate changes or to reduce the uncertainty in future climate projections, it is of great importance to disentangle the “direct” response to the solar signal from both natural and anthropogenic drivers and from the background “noise” represented by internal variability.
In this work we assess the response of the climate system to a solar grand minimum like the Maunder Minimum using the Isca intermediate-complexity General Circulation Model (GCM) from the University of Exeter, and possibly higher-complexity GCMs in the near future. We perform simulations with and without consis- tent ozone variations, thus isolating the contribution of the “top- down” stratospheric ozone-dynamic coupling from effects primarily driven by tropospheric dynamics. In this context, polar regions seem to play a key role as early or amplified indicators of solar-induced climatic changes.

Speaker: Lucaferri Lorenza (University of Rome Tor Vergata)

17:06 P28 - Relationship between solar activity and atmospheric circulation over Europe

There is growing evidence that solar variability associated with the 11-year sunspot cycle, particularly during solar minima and maxima, influences the troposphere. Numerous observational and modelling studies have linked the solar cycle to winter weather and climate variability in the Euro-Atlantic region. However, the strength of these links remains debated, owing to their reduced stability in extended records, inconsistent detectability across datasets and methodologies, and the seasonally dependent and time-lagged nature of the tropospheric response. Additional uncertainty arises from stratospheric processes, particularly the QBO and sudden stratospheric warmings, which can modulate solar signals through stratosphere– troposphere coupling.
This study investigates the relationship between solar variability and wintertime tropospheric circulation over central Europe by analysing the frequency of synoptic circulation types under different levels of solar activity during 1851–2022, using monthly mean sunspot numbers and the Groswetterlagen reanalysis classification of circulation types. By focusing on circulation- type frequencies, we provide a complementary view of the solar–circulation relationship and assess how solar activity influences tropospheric circulation at smaller temporal and spatial scales.
The results show a significant relationship between solar activity and tropospheric circulation; however, with clear differences between early and late winter. Under low solar activity, westerly types occur less frequently, indicating a suppression of zonal flow, in favour of a higher frequency of northerly types, particularly purely northerly ones. In contrast, under high solar activity, northerly types are significantly reduced, while westerly and south-westerly types are more frequent, predominantly in late winter. Anticyclonic situations occur more frequently under low solar activity, compensating for the reduced frequency of cyclonic types, predominantly in early winter. Finally, the circulation response is stronger during high- intensity solar cycles and weaker during low-intensity cycles.
In summary, solar variability modulates wintertime tropospheric circulation, with a clear subseasonal dependence: the response to low (high) solar activity is strongest in early (late) winter. The magnitude of the circulation response also varies with the amplitude of the solar cycle, and the contrast between early- and late-winter circulation patterns suggests a lagged tropospheric response to the solar signal.

Speaker: Hana Hanzlíková (Institute of Atmospheric Physics, Czech Academy of Sciences, Praha, Czechia)

17:07 P29 - Role of the Northern Polar Vortex and Geomagnetic Activity in Modulating Surface Solar Radiation and Solar Power Generation in Europe

In wintertime, the stratospheric polar vortex strongly influences European weather, affecting temperature, wind speed, and cloudiness. A strong polar vortex is typically associated with milder, windier, and cloudier conditions in northern Europe, while colder, calmer, and clearer weather prevails in southern Europe. Cloudiness directly controls the amount of solar radiation reaching the surface and therefore modulates solar power production.
One important factor influencing the polar vortex, and consequently surface weather, is energetic electron precipitation (EEP), for which the geomagnetic aa index can be used as a proxy. Enhanced EEP increases ozone loss in the upper atmosphere, leading to stratospheric cooling and a strengthened polar vortex. However, the influence of EEP on the polar vortex is strongest during the easterly phase of the quasi-biennial oscillation (QBO), which enhances planetary wave activity and meridional circulation transporting ozone toward polar regions. While the impacts of EEP on surface temperature and wind speed via the polar vortex have been investigated, its effects on cloud cover and surface incoming solar radiation remain largely unexplored.
In wintertime, countries in southern and central Europe receive sufficient solar radiation to produce a significant fraction of their electricity demand through solar power. In this study, we examine how winter cloud cover, surface incoming solar radiation, and solar power production respond to the strength of the polar vortex and geomagnetic activity across Europe. We find that stronger geomagnetic activity and stronger polar vortex in the easterly QBO phase are associated with reduced cloudiness and higher surface solar radiation in southern Europe, which enhances solar power production. For example, in Spain, the NAM index, which reflects the strength of the polar vortex, shows a correlation of 0.77 with solar power, while geomagnetic activity exhibits a correlation of 0.67. In both cases, the correlations are statistically highly significant.

Speaker: Veera Juntunen (University of Oulu, Finland)

17:08 Ionospheric irregularities in the polar regions - climatology and predictability

Instabilities and turbulence in the Earth ionosphere can lead to irregularities in the ionospheric plasma density. Ionospheric plasma irregularities are important space weather effects, which can significantly impact the propagation of radio waves through the upper atmosphere, and consequently degrade the quality of trans- ionospheric signals and communication with satellites. This can decrease the accuracy of positioning using the Global Navigation Satellite Systems (GNSS), such as GPS and Galileo, and can even lead to unavailability of such services. Therefore, a comprehensive understanding of ionospheric irregularities is vital for both research and operations that rely on satellite signals, and for the development of space weather forecasting services.
We present climatological studies of ionospheric irregularities in the polar regions carried out using the Swarm satellite data and ground-based measurements in the Arctic and in Antarctica. We discuss climatology of ionospheric irregularities in relation to the solar activity. With long term statistical studies, we show that the polar ionosphere in the Antarctic is in general more irregular than the Arctic. We also show how we employ ground- based data to develop an empirical model based on more than one solar cycle of the rate of change of the total electron content index (ROTI) maps, which now serves as a basis for regular services to forecast the level of ionospheric irregularities in the Arctic.
Finally, we present collaborative initiatives to advance our understanding on ionospheric plasma irregularities, as well as AGATA, which is the Scientific Research Programme of the Scientific Committee on Antarctic Research (SCAR). AGATA is a worldwide initiative that focuses on better understanding of coupling between and within atmospheric layers and geosphace in the Antarctic and also in the Arctic, and creates a platform for coordinated international efforts for comprehensive studies of the polar upper atmosphere.

Speaker: Wojciech J. Miloch (Department of Physics, University of Oslo, Oslo, Norway)

19:00 → 20:15 Welcome reception

Drinks and cold appetizers to mark the opening of the conference.

Wednesday 10 June

09:00 → 09:20 Presentation collection for Day 2, 3 and 4 (please prepare your file in .pdf or .pptx)

09:20 → 10:36 1.3 Long-term TSI/SSI variability (chair Laure Lefevre)

Convener: Greg Kopp (Colorado U., US)

09:20 The changing Sun: a review of TSI and SSI variability across time scales

Solar irradiance is the fundamental energy source powering the Earth system, and its variability over time is a critical factor in understanding climate dynamics. While Total Solar Irradiance (TSI) represents the overall energy output, it is the wavelength-dependent variability of Spectral Solar Irradiance (SSI), especially in the ultraviolet, that most directly influences atmospheric processes.
Solar output fluctuates on a vast range of timescales, from milliseconds to millennia, driven by processes from turbulent convection to the slow evolution of the Sun itself. However, assessing variations beyond the well- documented 11-year solar cycle presents a significant observational challenge. Space-based measurements rarely extend beyond a decade, making the construction of a reliable long-term irradiance record critically dependent on the precise intercalibration of data from successive and diverse missions. Reconstruction becomes even more complex when relying on sparse data from historical telescopic observations. To reconstruct TSI/SSI over millennial timescales, estimates of the open solar magnetic field are indispensable. Such TSI and SSI reconstructions rely on cosmogenic isotopes, which act as proxies for cosmic ray intensity. Cosmic rays, in turn, are modulated by the heliospheric magnetic field, reflecting variations in solar activity.
This presentation aims to synthesize key aspects of solar variability and present the latest state-of-the-art findings, reflecting the community’s ongoing efforts to reconstruct this complex dataset.

Speaker: Francesco Berrilli (Rome Tor Vergata U., IT)

09:40 Secular Trends in Solar Irradiance: From Direct Measurements to Model Reconstructions

The Sun is the primary external energy source for Earth, making reliable long-term records of solar irradiance essential. Measurements of total solar irradiance (TSI) have been available since 1978, although they originate from multiple relatively short-lived space-based missions that exhibit marked differences. Combining these observations into a consistent long-term record is therefore challenging and has resulted in several composite series, which imply conflicting long-term trends between activity minima.
To address the limited duration of direct observations, a range of modelling approaches has been developed to reproduce irradiance and reconstruct it over earlier periods. These models rely on observations for calibration and/or validation, but differ in the input data and their assumptions and treatment of solar magnetic features, leading to divergent long-term trends. Reconciling the secular trends inferred from direct TSI measurements and those from various irradiance reconstructions is therefore crucial, particularly for accurately assessing the solar influence on Earth’s climate. Here, I will give an overview of the current picture about long-term trends in direct irradiance measurements and the principal modelling approaches used to reconstruct solar irradiance.

Speaker: Theodosios Chatzistergos (Max Planck Institute for Solar System Research, DE)

10:00 Updates (Including Two ‘Final’ Final Updates) to Total Irradiance Monitor Data and a Survey of Solar Flare Observations in TSI

I have updated the total solar irradiance (TSI) data from all three spaceflight Total Irradiance Monitors (TIMs) within the last year, improving the accuracies and stabilities of the SORCE, TCTE, and TSIS-1 TIM measurements. These are expected to be the final data versions for the SORCE and TCTE instruments, both of which have been decommissioned, having been replaced by the continuing TSIS–1/TIM. These refined datasets are being incorporated into updated TSI composites spanning the 48-year, uninterrupted spaceborne TSI measurement record, to which all long-term solar-irradiance reconstructions are tied. I will summarize these data updates, present the associated changes for each of the three instruments, and compare their latest data with those from other concurrent, on-orbit TSI instruments.
Using the updated data, I have performed a survey of TIM observations of solar flares having magnitudes greater than X4 from 2003 to the present. TSI measurements of flares are the only means of measuring the entire radiant solar-flare energies, and I will compare those to the integrated GOES x-ray energies for the largest flares measured. Such flare observations have relevance for space climate and can be compared in magnitude and frequency to flares on other stars, where full-spectrum measurements cannot currently be acquired.

Speaker: Greg Kopp (Colorado U., US)

10:12 Reconstruction of annual solar irradiance over three millennia

Space-based measurements of solar irradiance since 1978 have revealed variability across all observable timescales. However, this record is too short to assess the Sun’s role in climate variability, making long-term irradiance reconstructions essential. From days to millennia, irradiance variability is dominated by changes in surface magnetism through the competing effects of sunspot darkening and facular brightening. Consequently, reconstructions of past irradiance variations rely on suitable proxies of solar magnetic activity.
The longest direct record of solar magnetic activity is provided by the sunspot numbers (SN), while information on facular evolution must be inferred indirectly. The SATIRE-T (Spectral and Total Irradiance Reconstructions for the Telescopic era) model reconstructs solar irradiance using the SN record as input. A recently revised version of the model is constrained by modern data, enabling an observation-based link between sunspot activity and the emergence of small-scale magnetic features such as faculae and network fields. Irradiance reconstructions based on telescopic SN show excellent agreement with direct measurements, reproducing about 90% of the observed variability.
To extend irradiance reconstructions into the pre-telescopic era, indirect proxies of solar activity are required. Concentrations of cosmogenic isotopes (14C and 10Be) preserved in terrestrial archives provide such information, but until recently these records were mostly available at decadal resolution. Recent advances in the treatment of cosmogenic isotope data have yielded annually resolved records over the past three millennia, enabling reconstructions of annual SN from them. Using these SN as input to SATIRE-T, we present the first physics- based reconstruction of total solar irradiance at annual resolution over this period.

Speaker: Duresa Temaj (Max Planck Institute for Solar System Research, DE)

10:24 Comparing direct and indirect proxies of centennial solar EUV irradiance

Sunspots offer a uniquely long view of solar magnetic activity, and depict large variability during the last 100 years, a period known as the Modern Maximum (MM). However, since weaker magnetic elements dominate solar surface magnetism, our view of solar magnetic variability would be incomplete if it was only based on the strongest magnetic fields of sunspots. Luckily, there are several long-term series of observations that can yield direct and indirect centennial proxies of solar EUV flux. Since solar EUV emissions mainly come from the chromosphere, both the solar EUV observations and their proxies can give information about the long-term evolution of moderately-strong magnetic elements of plages and magnetic network. Independent measurements of solar magnetic fields of different strength can give interesting information about the long-term evolution of the structure of solar magnetic fields during the MM when solar activity was dramatically changing.
We have recently developed a centennial EUV proxy from the daily variation of the geomagnetic Y-component measured at eight long-operating observatories. This proxy, the rY index, was used as a solar activity proxy already in the 1860s by R. Wolf. We found that the rY index has a temporally changing relation with sunspots over the MM, indicating that the strongest and moderate magnetic field elements evolve differently over the MM. Here we study several direct and indirect long-term proxies of solar EUV activity and compare their mutual relation over the MM, as well as their relation with different sunspot-related photospheric variables. Our results further verify the different evolution of magnetic field elements of different strength over the Modern Maximum, indicating a systematic difference in the magnetic evolution between the photosphere and the chromosphere with long-term solar activity. We also discuss the consequences of our results to solar driving of the ionosphere and to the implied long-term variation of the spot-facula ratio and the stellar evolution of the Sun and Sun-like stars.

Speaker: Kalevi Mursula (Oulu U., FI)

10:36 → 11:00 Coffee break

11:00 → 11:56 1.4 Solar activity and eruptions in the long-term prospective (chair Timo Asikainen)

Convener: Allan-Sacha Brun (CEA Paris-Saclay, France)

11:00 Solar energetic particle acceleration and escape into the heliosphere

High energy ions and electrons play a crucial role in the fast energy transport in solar flares. A fraction of the particles accelerated in flares precipitate in the solar atmosphere, heating the corona and chromosphere, and producing non-thermal gamma-, X-ray and radio emissions. Others escape from the corona into the heliosphere. The escaping energetic particles are an important component of the space weather.
Recent advances in computational and observational studies of solar energetic particles, have significantly improved our understanding of how particles are transported in the solar corona, and from the corona into the heliosphere, particularly thanks to the unprecedented data from Solar Orbiter and Parker Solar Probe missions. In this talk, I will review the current progress in studies of solar particle acceleration and escape into the heliosphere, with an emphasis on data-constrained computational modelling. I will also present our latest results of magnetic reconnection and particle acceleration modelling in individual solar flares, focusing, in particular, on the effect of magnetic configuration and the location of the acceleration site on the properties of escaping energetic particles.

Speaker: Mykola Gordovskyy (U. of Hertfordshire, UK)

11:20 Historical Records for Space Climate Studies: Some Recent Advances

Recovering historical solar and geomagnetic observations is essential for extending the temporal baseline of Space Climate research. A significant amount of valuable material remains scattered across solitary archives or published in sources that are largely inaccessible to the research community. In this contribution, we present recent progress in identifying, analyzing, and contextualizing several sets of historical records relevant to long-term solar variability.
First, we revisit early sunspot observations made in Spain. These include the records of Diego Torres Villarroel during 1744, the observations of Lorenzo Hervás Panduro in 1791, and several additional isolated observations that help to fill existing gaps. We also highlight a rarely cited 1921 report by F. Damián y Manté describing a striking hexagonal sunspot, an unusual morphology that attracted contemporary scientific interest.
Second, we survey early observations of solar flares, emphasizing both their historical evolution and their potential contribution to Space Climate reconstructions. Special attention is given to the exceptional observation made by J. Birmingham on 6–7 May 1871, which may correspond to a recurrent white-light flare, an event of considerable interest for constraining extreme solar activity in the 19th century.
Third, we examine several cases of historical auroral sightings. These include reports associated with the 1588 expedition of the “Invincible Armada,” as well as documented observations by Fathers Feijóo and Isla during the 18th century. Additional noteworthy events are discussed for their relevance to understanding past geomagnetic disturbances at mid and low latitudes.
Together, these findings demonstrate the scientific value of re-examining historical sources. Such records, once properly analyzed and integrated, provide unique insights into long-term solar behavior, help refine reconstructions of past space weather and space climate conditions, and contribute to a more complete understanding of extreme solar- terrestrial phenomena.

Speaker: José Manuel Vaquero (Universidad de Extremadura, ES)

11:32 Energetic Particles from Strong Interplanetary Shocks in November 2025 and January 2026

We present a preliminary analysis of two recent periods of quasi-extreme space weather driven by strong interplanetary (IP) shocks. In November 2025, four fast CMEs occurred within five days, each associated with an X-class flare. Although the third event had the highest soft X- ray peak flux and CME speed, giving rise to a ground level enhancement (GLE) event, it was the shock wave from the second eruption that was more surprising. It arrived much earlier than expected, causing not only a G5 geomagnetic storm but also a very rare energetic storm particle (ESP) event extending beyond 100 MeV. In January 2026, an apparently isolated CME (also associated with an X1.9 flare) drove a shock wave that remained strong when it arrived at 1 AU. The resulting ESP event reached the >10 MeV flux levels not observed since 1991 March 22 but its spectrum was very soft, in sharp contrast to the November 2025 event. This shock was again responsible for a G5 (Kp=9-) geomagnetic storm. We evaluate the relative roles of intrinsic CME properties and interplanetary preconditioning for producing these quasi-extreme radiation storm conditions of different kinds. Comparing them with other historical events that showed very high >10 MeV proton fluxes, we discuss the possible solar cycle dependence of how CME-driven shock waves evolve in the heliosphere.

Speaker: Nariaki Nitta (Lockheed Martin Solar and Astrophysics Laboratory, US)

11:44 Prospects of Spectral Microwave Observations of the Sun in Latvia

Known that spectral observations of microwave (1-10 cm) polarized emission of the Sun offer the possibility for direct measurements of plasma parameters and magnetic field inductions in the upper chromosphere and the lower corona at the range of heights above the photosphere. Thus current microwave observations of the Sun could be expected for studies of wide range of solar physics problems understanding solar activity features and origins of the space weather creation.
For last years Ventspils International Radio Astronomy Centre (VIRAC) of Ventspils University of Applied Sciences, Latvia develops and provides spectral polarimetric microwave observations of the whole disk of the Sun and its separate active regions. Observations are performed with the RT-32 radio telescope in a “single dish” mode. The radio telescope is equipped by the multichannel (12 frequency channels) spectral polarimeter and is able to observe the solar emission at 2.1-7.4 cm (4.1-14.3 GHz) wavelength range and both circular polarizations simultaneously.
The presentation concerns to a current state solar microwave observations in VIRAC, its technical and methodical issues and some projects VIRAC participated in. Also the presentation discusses feasible problems of solar physics which could be studied on the base of these microwave spectral polarimetric observations. The possibility of studies of coronal holes and coronal hole-like areas (“dark coronal corridors”, “coronal partings”, “s-web”) associated with local open magnetic fields which could be expected as sources of the slow solar wind and the analysis of microwave flux fluctuations of active regions preceding solar flares are discussed as well.

Speaker: Dmitrijs Bezrukovs (VIRAC, LV)

11:56 → 13:11 1.5 Solar-stellar relations and 3.5 Space climate at other planets (chair Nandi Dibyendu)

Conveners: Alexander Shapiro (University of Graz, AT), Vladimir Airapetian (NASA)

11:56 Solar and stellar magnetic activity and variability

All stars with an outer convection zone are magnetically active at some level, with the amount of activity depending on stellar parameters, e.g. the effective temperature and the rotation rate. By far the best studied such star is the Sun. While investigating other stars allows studying stellar activity across a broad range of stellar properties, the Sun provides us with the unique opportunity of resolving a stellar surface and atmosphere in detail so that the physical processes taking place there can be probed close to the spatial and temporal scales at which they occur. It is from the Sun that we know that, excepting differential rotation and meridional circulation that drive the solar dynamo, the most important interaction for its activity and variability takes place between the magnetic field and surface convection. This interaction leads to an assortment of magnetic features at the solar surface, whereby the properties of such features depend on the amount of magnetic flux present at their location and in their vicinity. Recent years have seen considerable progress in our knowledge and understanding of solar variability and activity thanks to new instruments, telescopes and space missions as well as improved numerical simulations. On the stellar front, highly sensitive observations carried out by space missions aiming to detect and characterize exoplanets have led to an explosion in observations of stellar variability. The advances in understanding and quantitatively modelling solar variability have also paved the way to a better understanding of the variability seen in other sun-like stars. An introductory overview and selected highlights of recent results will be presented in this talk.

Speaker: Sowmya Krishnamurthy (University of Graz, AT)

12:16 Active Regions and Variability Across Main-Sequence stars

Stellar magnetic activity, manifested in spots, faculae, and brightness variability, depends sensitively on fundamental parameters such as stellar mass, age, rotation, and metallicity. Understanding how these factors shape active regions is essential not only for interpreting other stars, but also for placing the Sun into its proper stellar context.
Three-dimensional radiative magnetohydrodynamic (MHD) simulations of the solar photosphere now provide a realistic framework for modelling magnetoconvection and emergent intensity contrasts. The next step is to extend this physically consistent approach beyond the Sun. In this talk, I present a grid of 3D radiative MHD models spanning F, G, K, and M stars, enabling a systematic comparison of active-region properties along the main sequence.
The models reveal clear departures from what is observed on the Sun. Facular regions, bright in the solar case, progressively lose contrast towards cooler effective temperatures and become dark from approximately spectral type M2 onwards. In addition, metallicity significantly modulates radiative contrasts, with enhanced metallicity favouring darker facular signatures even at otherwise solar parameters. These results demonstrate that magnetic activity cannot be interpreted solely through a solar lens: stellar type and composition fundamentally reshape the observable manifestations of active regions.

Speaker: Veronika Witzke (University of Graz, AT)

12:36 Modeling granulation induced variability in spectral lines: lessons from the Sun

Granulation is a fundamental manifestation of near-surface convection in cool main- sequence stars and plays a central role in regulating photospheric structure, spectral variability, and radiative output. Understanding its imprint on spectral lines is essential for connecting solar observations with unresolved stellar measurements and for improving models of stellar surface convection.
In this study, we analyse high-resolution MPS-ATLAS specific-intensity spectra emerging from the solar photosphere, simulated using the 3D radiative magnetohydrodynamic code MURaM, and investigate spectral line variability induced by granulation. We present a novel methodology based on the spatial variability of spectral line strengths and wavelength shifts and use it to examine the differential response of lines from neutral and singly ionised species to convective inhomogeneities.
We identify a clear and systematic distinction in the behaviour of these two groups. Temperature and velocity contrasts between granules and intergranular regions have a greater effect on the strengths of neutral lines and on the wavelength positions of singly ionised lines. This differential sensitivity provides new diagnostics of the thermodynamic and dynamic structure of granulation and establishes a framework for interpreting unresolved stellar spectra.

Speaker: Sowmya Krishnamurthy (University of Graz, AT)

12:48 Local and Galactic scale factors of habitability of Earth and exoplanets, from a Space Climate perspective

In its travel through the Milky Way, the Sun traverses a variety of Galactic environments, including dense interstellar clouds. Astronomical effects on Earth’s past climate have been limited to 10,000-year scales variations in Earth’s orbital parameters while our recent studies suggest that longer-term climate shifts that occur every few million year may be linked to compression of the heliosphere (the “cocoon” formed by the solar wind) when the Sun crosses dense clouds as it travels through the Milky Way. During such periods Earth was exposed to increased radiation and large amounts of hydrogen, potentially altering its climate. These events are consistent with independent $^{60}$Fe records indicating nearby astrophysical encounters at ~2–3 and ~6–7 million years ago (Ma), as well as $^{10}$Be anomalies near ~10 Ma that may reflect prolonged exposure to enhanced radiation during a cold cloud crossing. A convergence of recent advances across astronomy, space physics, and paleoclimate creates an unprecedented opportunity to rigorously test this hypothesis. We now have high-precision astrometry from the Gaia mission that allows one to reconstruct the Sun’s trajectory through the Galaxy and to identify, with remarkable accuracy, the interstellar structures it has encountered over the past ~10 Ma. Major theoretical and modeling advances now enable quantitative predictions of how the heliosphere evolved during these encounters. I this talk I will discuss our recent work that show that during such periods, Earth was exposed to increased radiation and large amounts of hydrogen. I will discuss our preliminary results that show that the increase in hydrogen augmented mesospheric water vapor, leading to increased formation of both polar mesospheric clouds and polar stratospheric clouds. The amount of radiation that Earth experiences from such events depends on the duration of the crossing and the amount of compression of the heliosphere, with implications for Earth’s climate. I will discuss our results as well that indicate that high temporal 10Be signal in ocean records and ice cores can distinguish between alternative scenarios such as supernova explosions and cold cloud crossings. Finally, I will comment on the consequences of these studies for understanding long-term climate variability and assessing planetary habitability across the galaxy.

Speaker: Merav Opher (Boston University, US)

13:11 → 14:10 Lunch

Baked rainbow trout (1st option) or salt-baked bundle beets (2nd option) with Sandefjord sauce, fennel, cucumber, and dill potatoes
Including water, salad, bread, butter and coffee/tea

15:00 → 21:00 Excursions

1 OPTION: Hiking in Åland/Ahvenanmaa (6 hrs from 15.00, for ages 7 and up only). Start your tour with a coach drive to North of Åland, to Geta Berget. On your way you can admire the big Apple tree gardens and small villages. Arrive to the most Northern part of the main Island where the nature is barren and rocky surrounded by open sea. From here you will start your nature hiking with a guide. Getabergen Hills lie 107 metres above the sea level and offer fantastic vast sea views in a barren rocky nature with low pine trees. The nature trail is easy (downwards) to moderate (upwards), and the trail leads mainly over smooth flat red granite rocks and nature paths with low vegetation (can be slippery after rain). No stairs.
The first part of the trail slopes slightly downwards towards the seafront and along the trail there are interesting cave-like rock formations at Getagrottan, used as shelter for the locals during the Great Northern war in the 18th century. The path leads down to the waterfront, Djupviken Bay from where the trail turns back and goes uphill to the starting point. The route is approximately 5 km long. A refreshment stop is done during this tour at café Soltuna (you can preorder a dinner for 19€/pers ). Before you re-join the coach you have time take photos and admire the nature.

2 OPTION: Guided tours of the Åland Maritime Museum and onboard the tall ship Pommern (2 hrs from 15:00). Åland Maritime Museum manages and mediates Åland’s maritime heritage, with reference to the present and to the future. The origins lie in the 1920s when Åland sea captain Carl Holmqvist started to collect nautical objects, realising the days of sailing ships were over. In 1935 he co-founded Åland Nautical Club with the aim of establishing a maritime museum for Åland. The museum building, designed by architect Jonas Cedercreutz, was completed in 1949 and five years later the Åland Maritime Museum opened to the public.
Through contributions from Åland seafarers and shipping companies the collections continued to grow. In 1986 Åland Nautical Club donated all museum objects, archives and the library to the newly formed trust Åland Maritime Museum.
An extension as well as comprehensive renovation of the original building commenced in the autumn of 2009. The museum re-opened on 26th April 2012. The original building, drawn by Jonas Cedercreutz in the 1940’s, got an extension designed by architects Johanna Vuorinen and Esa Kangas. The exhibition lay-out was designed by Helsinki-based studio Amerikka, in cooperation with Jouni Kaipia. In March 2015 the Trust was entrusted full management of the historic tall ship Pommern, owned by the Town of Mariehamn. A major investment in the visitor experience on board has since been done; as well as the building of a dry dock that Pommern moved into in 2019.

Thursday 11 June

09:00 → 10:30 2.1 Cosmic rays and modulation (chair Mike Lockwood)

Convener: Monica Laurentza (INAF, IT)

09:00 Long-term solar modulation of cosmic rays

In this talk I’ll give a brief introduction to the physics of cosmic ray modulation in the heliosphere and the time-dependent drivers thereof. The Parker transport equation formalism, used to model solar modulation, will also be introduced, along with a discussion regarding the necessary input parameters. A frequently applied approximation to the Parker transport equation, especially when very long-term modulation is studied, is the so-called Force-field approximation. I’ll show where this approximation originates from, what approximations are made during its derivation, why it seems to work, and what we can learn from applying this approximation to historical cosmic ray observations and proxies.

Speaker: Roelf Du Toit Strauss (NWU, ZA)

09:20 Short-term modulation of galactic cosmic rays by interplanetary transients

Galactic cosmic rays (GCRs) constitute a continuous flux of high-energy particles, mostly protons and helium nuclei, flowing through the Heliosphere and interacting with solar wind and interplanetary magnetic field. The result of this interaction on long periods of time is the well-known modulation of the low end of the GCR energy spectrum (below a few GeVs), following the 11-year activity cycle of the Sun and the 22-year cycle of global solar magnetic field polarity reversals. On smaller time scales, GCRs become powerful diagnostics of interplanetary transient structures such as interaction regions between fast and slow solar wind streams and interplanetary coronal mass ejections (ICMEs). These structures are characterized by enhanced turbulence, shocks, large-scale plasma compressions, magnetic flux-ropes, and other phenomena that can inhibit the particle transport and induce a decrease in the GCR flux. Such depressions have been routinely observed from ground- and space-based instruments over several decades, and are known as Forbush decreases. In this talk, I review the main observational properties of the short-term GCR modulation driven by interplanetary transients. By combining ground-based observations from the worldwide neutron monitor network with multipoint measurements from spacecraft at different locations in the heliosphere, it is possible to investigate how the main properties of GCRs (e.g., energy spectrum) vary in time during a transient event. In addition, the analysis of directional responses from neutron monitors allows us to study how interplanetary magnetic field structures induce anisotropies in the GCR flux, especially during strong disturbances such as fast and magnetically complex ICMEs. These observations provide important constraints on particle transport processes (such as diffusion, drift, and cross-field transport) and place GCR short-term modulation within the broader context of space weather, as the same interplanetary structures that modulate GCRs can drive solar energetic particle events and geomagnetic disturbances.

Speaker: Simone Benella (INAF-IAPS, IT)

09:40 Ground level enhancements of Solar Cycle 25

Methodological study of solar energetic particles (SEPs) gives the basis to reveal their origin, acceleration and also top constrain the models of their propagation in the interplanetary space. It is believed that SEPs are produced following solar eruptive processes, such as solar flares and/or coronal mass ejections. SEPs can be accelerated to approximately 10 GeV/n range, yet the bulk are with energies of about 100 MeV/n. When SEPs are in the GeV range, they can induce a particle shower in the Earth’s atmosphere in which secondaries can be registered by ground-based detectors, such as neutron monitors (NMs). This class of events is called ground-level enhancements (GLEs). The current solar cycle 25 produced several events, namely the quite interesting event that occurred on 11 May 2024 observed during the deep phase of a significant Forbush decrease and one of the greatest geomagnetic storms as well the event on 11 November 2025, which was among the strongest ones. Here we present results from observations and analysis of the GLE events of solar cycle 25, focusing on the spectral and angular characteristics of the SEPs. Possible acceleration mechanisms based on the obtained results are discussed.

Speaker: Alex Mishev (Oulu U., FI)

09:52 First Ground-Level Enhancement (GLE) events #1–4 digitized from historical sources

The Sun sporadically produces solar energetic particle (SEP) events that can significantly vary in intensity and spectral hardness. Although the majority of such events miss the Earth or are too weak to be registered by ground-based particle detectors, there are rare occurrences when strong SEP events penetrate deep into the atmosphere and can be observed on the ground. The latter ones are called “Ground-Level Enhancements” (GLEs) because they are seen as enhancements of the count rate over the background in records of ground-based neutron monitors. So far, there have been 77 GLEs registered since the beginning of the 1940s. Starting from GLE #5, they were detected by neutron monitors, digitized and analysed. Those experimental data played a key role in studies of particle acceleration and propagation at and in the vicinity of the Sun. However, the first four events (GLEs #1-4), recorded in the 1940s, were neither registered into the International GLE Database nor analysed in detail , mainly because they were observed by non-standard instruments, and their origin and importance were not fully understood at that time. There were significant difficulties in the interpretation of the data , such as scattered sources, almost always missing tabular data, often insufficient instrumental descriptions, etc. In preparation for future analysis of the events, we identified historical records containing observations of GLEs #1-4, compiled metadata, described the used instruments, digitised cosmic-ray measurements from figures, verified the results, assessed digitisation uncertainties, normalised in a standard for the GLE analysis way, and made the digital data available in the International GLE database (https://gle.oulu.fi) and published as Hayakawa et al. (2026). The results in their finalised form are presented in this contribution.

Speaker: Stepan Poluianov (Oulu U., FI)

10:04 Analysis of the energy spectrum of the long-term GCR variations based on the AMS-02 data

Using data from the AMS-02 instrument aboard the International Space Station, we examined long- term variations of the galactic cosmic ray (GCR) proton fluxes. This dataset enables a high-resolution study of time profiles and rigidity dependence within a rigidity range of 1 to 100 GV. We investigated the amplitude of long-term GCR variations using a power-law fit across the solar cycle. To understand the underlying physics, we correlated GCR variations with heliospheric magnetic field (HMF) turbulence, specifically analyzing power spectral density frequency exponents. During the studied period, the spectral index of the power-law rigidity spectrum exhibited clear solar cycle variability. Notably, the index tended to be higher during the solar maximum than during the solar minimum. The study provides evidence of an energy-dependent rigidity spectrum for long-term GCR variations: we observed a soft rigidity spectrum of GCR intensity variations for solar maximum and during the minimum a hard rigidity spectrum. These shifts are attributed to significant temporal rearrangements in the HMF turbulence structure between solar activity maximum and minimum. Moreover, AMS-02 data indicates a progressive softening of the spectra toward higher energy levels.

Speaker: Agnieszka Gil-Swiderska (Siedlce U., PL)

10:16 The near-Earth modulation (NEM) index in high cadence for study of global cosmic ray modulation and space climate

The magnetic activity of the Sun modulates the fluxes of galactic cosmic rays (GCRs) arriving to the heliosphere and Earth. This modulation of GCR can be estimated by a straightforward force-field approach, which reduced the modulation to a single parameter φ with units in megavolts. Even though the physical interpretation of this modulation parameter can be unclear, it can still assess the overall modulation efficiently and relatively accurately.
Since the GCR particles can take from weeks to months to travel from the heliospheric boundary to Earth, the heliospheric modulation parameter is usually recorded in monthly and yearly resolution. Recent work, however, has revealed that the parameter also functions very successfully even in daily, hourly and even minute resolutions during quiet conditions, which can be utilized to monitor the near-Earth radiation environment and related events. The higher cadences mean that parameter is biased to near-Earth space, due to which we call the higher resolution version the near-Earth modulation (NEM) index.
We present recent results of the NEM index at daily, hourly and minute cadences, used methodology and related datasets of neutron monitor data and rigidity cutoff computations. The hourly resolution result includes data from 38 neutron monitors stations from years 1951- 2026, total up to 1491 years of hourly cadence observetations. We find that the parameter performs well with up to +-1 % accuracy to expected values during quiet times. During Forbush decreases and other disruptions there are station-specific deviations from the expected values during the shock and flux rope phases, revealing information about anisotropy during the events. We discuss potential use cases, such as the analysis of Forbush decreases and CME’s, NM data quality assessment and real-time-monitoring of the near- Earth radiation environment and dose rates. We also discuss preliminary results on 5-minute and higher resolutions.

Speaker: Pauli Väisänen (Oulu U., FI)

10:30 → 10:50 Coffee break

10:50 → 12:46 2.2 Long-term evolution of CMEs and solar wind and 2.3 Geomagnetic storms and superstorms (chair Merav Opher)

Conveners: Emilia Kilpua (Helsinki U., FI), Maxime Grandin (Helsinki U., FI)

10:50 Space Weather Impacts of Coronal Mass Ejections

Our Sun is a dynamic star that produces energetic events known as coronal mass ejections (CMEs). These ejections are driven by the Sun's magnetic fields, which facilitate their movement through the heliosphere. The propagation of CMEs is primarily affected by the ambient solar wind medium, which ultimately influences their arrival time. In general, the magnetic field configurations on the Sun and the background solar wind play a significant role in how CMEs travel through interplanetary space, determining their travel time and their magnetic field properties when they impact the Earth. Thus, CMEs play a crucial role in shaping space weather, influencing both the heliosphere and geospace. As the solar activity varies with time, the effects of CMEs in the near-Earth environment can also significantly vary and differ from one event to another.
I will discuss the effects of coronal mass ejections (CMEs) on Earth, focusing on the geoeffective event of Solar Cycle 25 in April 2023, which resulted in an intense geomagnetic storm. We employ advanced observational and modeling methods and integrating multi-wavelength and multi-point remote sensing observations of this event, to study the propagation of the CME from the Sun to Earth. Further, we utilize the interplanetary flux rope simulator (INFROS) model to forecast the magnetic vectors of the interplanetary CME (ICME) at 1 AU. Additionally, we combined INFROS with the Drag-Based Model (DBM) and empirical Dst prediction models to create a space weather modeling framework aimed at estimating the severity of the related geomagnetic storm. The April 2023 event offered a distinctive chance to assess the space weather implications i.e. ionospheric and geomagnetic effects. The study demonstrates significant longitudinal asymmetries in ionospheric response and highlights the varying geomagnetic signatures associated with ICME substructures. The combined analysis underscores the importance of electric fields, neutral winds, and solar wind drivers in governing magnetosphere–ionosphere coupling during intense space weather events. I will also discuss the limitations and challenges linked to modeling such occurrences for improving space weather forecasting.

Speaker: Nandita Srivastava (Udaipur Solar Observatory, IN)

11:10 Magnetic Structure and Topology of CMEs: From Realistic Ejecta Representation to Helicity Decomposition

Coronal mass ejections (CMEs) are still modelled as isolated, highly twisted, circular flux ropes, a picture that forms the basis of many reconstruction methods and much of present-day space-weather work but that no longer matches the magnetic complexity revealed by recent data and simulations. In this talk, in situ and multi-spacecraft measurements, remote observations, and numerical modelling will be brought together with topological tools to outline a more realistic view of CME magnetic structure and its evolution from the low corona to 1 au and beyond. Observational constraints on twist, writhe, open–closed connectivity, aspect ratios, and coherence will be summarized, and particular attention will be paid to where they conflict with the classical, cylindrically symmetric, force-free flux-rope picture. A helicity-based framework will then be outlined in which CME structure is described in terms of self (twist and writhe) and mutual helicity between multiple flux systems, with winding numbers evaluated from 3-D simulations propagated to 1 au. For a representative simulated Sun–Earth CME, the total helicity is found to receive substantial contributions from twist, writhe, and mutual helicity between distinct flux regions, with mutual helicity accounting for a significant fraction of the total and writhe being of the same order as twist within the core flux rope. Taken together, these findings are interpreted as indicating that standard 1-D in situ fitting tends to overemphasize twist, that CME structures consistent with the observations need not be strongly twisted, and that forecasting and Sun–heliosphere coupling studies should explicitly account for writhe, mutual helicity, and the coexistence of open and closed field lines within the ejecta

Speaker: Nada Alhaddad (University of New Hampshire, US)

11:30 Voyager observations of 48 years of solar wind and its effects on the interstellar medium

The Voyager 1 and 2 spacecraft have traversed the heliosphere and entered the local interstellar medium (LISM). They are 169 AU and 142 AU from the Sun, 48 and 23 AU past the heliopause. These spacecraft have been taking data for over 48 years, more than four solar cycles. Thus they provide an excellent study of long-term time dependence of the solar wind. Solar cycle effects dominate the large-scale structure of the solar wind and continue to effect the LISM. Solar activity at and after solar maximum drive pressure pulses through the supersonic solar wind which are then observed in the shocked heliosheath plasma. These heliosheath pulsed then drive shock into the LISM generating plasma and radio waves which propagate deep into the heliosphere. Longer term pressure increases occur once per solar cycle and generate magnetic field and density increases far beyond the heliopause. This talk will discuss the present state of knowledge of the interaction of the heliosphere with the LISM and the effects of long-term changes in the solar in this interaction.

Speaker: John Richardson (MIT, US)

11:42 Coronal Mass Ejections: What We Now Know from 5 Solar Cycles of In-Situ Measurements about their Properties and Impact

Coronal mass ejections (CMEs) have been measured in situ since the 1970s with missions such as Helios, Voyager, IMP-8, Voyager. Over the past 30 years, we have now gained routine measurements by Wind and ACE at the Sun-Earth L1, in the inner heliosphere by STEREO, and in the innermost heliosphere and corona by Solar Orbiter and Parker Solar Probe. With 1000s of measurements from heliocentric distances of a fraction of an AU to several tens of AU, a better understanding of the average properties of CMEs and how it varies with both solar cycle and distance can be obtained. Additionally, the passage of STEREO-A by the Sun-Earth line during the maximum of solar cycle 25 combined with L1 and Solar Orbiter measurements, reveal for the first time the typical angular width of CMEs, and how their properties vary longitudinally. Such measurements are key to better constrain inputs of mid-term heliospheric evolution and to better understand space weather and solar wind-magnetospheric coupling.
I will summarize results from recent studies showing that the axial and poloidal components of the CME magnetic field decrease similarly with distance, and discuss how it must be reconcile by theoretical and fitting model. I will also show that CME properties for long-term heliospheric evolution models cannot be taken from remote observations, as those only capture the CME density and speed. Multi-spacecraft measurements of CMEs reveal conclusively that the magnetic ejecta of CMEs is narrower than previously thought and that CMEs have a complex combination of coherence and lack of coherence within their cross-section.

Speaker: Noé Lugaz (University of New Hampshire, US)

11:54 Superstorm and Supersubstorms of May 2024

The May 2024 superstorm (SYM-H peak = –518 nT) was characterized by a three-step main phase, a long and strong recovery phase, and six isolated supersubstorms (SSSs; SML < –2500 nT). The events were associated with multiple interplanetary sheaths and magnetic clouds. In this presentation, we will discuss unique interplanetary phenomena leading to the events, distinguished geomagnetic features, and extreme magnetospheric-ionospheric impacts of the events. Comparisons with previous extreme events in the space age will be presented as well.

Speaker: Rajkumar Hajra (USTC, CN)

12:14 Exploring Stormtime Geospace as a Complex System

Geospace is a complex, interconnected system, where diverse physical domains and particle populations interact across a vast range of spatial and temporal scales. To understand geospace in all of its complexity and enable robust space weather prediction, physics-based models must describe the system holistically, i.e., treat all essential processes and domains, while maintaining sufficiently high resolution to capture all the relevant scales. The NASA DRIVE Center for Geospace Storms (CGS) addresses this challenge through the development of the Multiscale Atmosphere-Geospace Environment (MAGE) model, which effectively bridges the gap between global dynamics and mesoscale regional processes. We present a summary of the results from the Center over the past few years that highlight how mesoscale processes drive global reconfiguration, including the build-up of the ring current via plasma sheet flows in the magnetosphere, the ionospheric response through subauroral polarization streams and plasma density plumes, as well as the interplay between mesoscale auroral forms and global electrodynamics. We conclude by placing these representative cross-scale coupling processes in the context of the global mass and energy redistribution characteristic of stormtime geospace dynamics.

Speaker: Slava Merkin (JHU APL, US)

12:34 Perfect-storm simulation vs. the 2003 Halloween storm: geoelectromagnetic response to sudden storm commencements

Intense geomagnetic storms are typically initiated by fast coronal mass ejections (CMEs) preceded by a sheath region of compressed solar wind. The arrival of the interplanetary shock at the magnetopause produces a sudden storm commencement (SSC), observed as an abrupt, step-like enhancement of the horizontal geomagnetic field. The rapid magnetic field variations associated with SSCs induce strong geoelectric fields at the Earth’s surface, which can pose significant risks to ground-based technological infrastructure. In this study, we compare geoelectric fields induced during two SSC events: (1) the SSC associated with the idealised perfect interplanetary CME simulated by Welling et al. (2021, doi:10.1029/2020SW002489) using the Space Weather Modeling Framework (SWMF), and (2) the observed SSC of the 29 October 2003 Halloween geomagnetic storm. This investigation supplements a recent study by Viljanen et al. (2026) which compared the simulated Carrington event without an SSC (Blake et al., 2021, doi:10.1029/2020SW002585) to the Halloween storm, and showed that a Carrington-like event can produce 4-10 times larger geoelectric fields.
For the idealized SSC event, the SWMF provides the external 1-s ground magnetic field due to ionospheric, magnetospheric, and field-aligned currents. Using a three-dimensional conductivity model of Fennoscandia, we derive the internal part of the magnetic field produced by telluric currents, thus, obtaining the total field variation, and the geoelectric field at the Earth’s surface. For the 29 October 2003 Halloween storm SSC, ground magnetic field measurements from the stations of the International Monitor for Auroral Geomagnetic Effects (IMAGE) network are employed to calculate geoelectric fields within the same conductivity model. We are especially interested in the peak amplitudes of the time derivative of the ground magnetic field (dB/dt) and of the geoelectric field. From the 1-s recordings of the Halloween storm, we know that the total horizontal dB/dt reached values up to 180 nT/s, whereas the maximum external dB/dt by the SWMF simulation is about 500 nT/s. When the telluric contribution is added to this, the total dB/dt is probably significantly larger, making a perfect SSC many times stronger than the Halloween SSC. A similar feature is expected for the geoelectric field, meaning that an extreme SSC can produce very large geomagnetically induced currents in power grids.

Speaker: Elena Marshalko (FMI, FI)

12:46 → 13:45 Lunch

Grilled chicken (1st option) or Grilled halloumi (2nd option) with Dijon-tarragon sauce, carrot, pickled onion, and rice.
Including water, salad, bread, butter and coffee/tea

13:45 → 15:45 3.1 Extreme events and worst-case scenarios (chair Agnieszka Gil-Świderska)

Convener: Florian Mekhaldi (Stockholm U., SE)

13:45 Four Millennia of Solar Activity from ¹⁴C in Tree-Ring

The Sun is the primary energy source of the Earth system, and variations in solar activity can significantly influence climate. While direct observations of solar activity, such as sunspot records, extend back only about 400 years, cosmogenic radionuclides produced by cosmic rays and preserved in tree rings and ice cores provide valuable proxies for reconstructing solar variability over millennial timescales [1]. However, the limited temporal resolution of most long, precisely dated cosmogenic nuclide records constrains investigations of short-term solar variability, including the 11-year Schwabe cycle and solar energetic particle (SEP) events. Recent advances have yielded several new high-precision, annually resolved radiocarbon (14C) tree-ring records. Here, we present a continuous atmospheric 14C records spanning the past 4,000 years. These annually resolved datasets enable a detailed investigation of short- term solar variability. Spectral and time-series analyses reveal clear signatures of the 11-year solar cycle and provide constraints on potential SEP events. Our results indicate that the 11- year solar cycle has persisted over millennia, at least during periods of grand solar maxima.

[1] E. Bard, G. Raisbeck, F. Yiou,& J. Jouzel, Solar irradiance during the last 1200 years based on cosmogenic nuclides. Tellus B 52, 2000

Co-author list:
Marcus Christl (1), Charlotte Pearson (2), Alex Bayliss (3), Timothy Knowles (4), Kurt Nicolussi (5), Thomas Pichler (5), Rashit Hanterimov (6), Lukas Wacker (1)

1) Laboratory of Ion Beam Physics, ETH Zurich, Otto‑Stern‑Weg 5, Zurich, Switzerland
(2) Laboratory of Tree Ring Research, University of Arizona, Bryant Bannister Tree‑Ring Building, 1215 E. Lowell Street, Tucson, AZ 85721‑0045, USA
(3) Historic England, Cannon Bridge House, 25 Dowgate Hill, London EC4R 2YA, UK
(4) Bristol Radiocarbon Accelerator Mass Spectrometry Facility, University of Bristol, Bristol BS8 1TS, UK
(5) Department of Geography, Universität Innsbruck, Innrain 52, 6020 Innsbruck, Austria
(6) Laboratory of Dendrochronology, Institute of Plant and Animal Ecology, Ural Branch of the Russian Academy of Sciences, 8 Marta Street 202, Ekaterinburg 620144, Russia

Speaker: Nicolas Brehm (ETH, CH)

14:05 Multi-Regional Radiocarbon Evidence for Unusual Solar Behaviour in the Late Middle Holocene

Annual-resolution ¹⁴C records from tree rings have become powerful proxies for detecting extreme solar behaviour, including short-lived cosmic-ray enhancements related to solar energetic particle (SEP) events and variations in solar magnetic activity. A recent study compiling an annually resolved ¹⁴C record from 1–970 CE, based on five new and three existing tree-ring series measured at the Curt-Engelhorn-Center Archaeometry (Germany) and the Centre for Isotope Research at the University of Groningen, demonstrated the potential of such datasets. Using statistical carbon-cycle modelling, adaptive decomposition of solar cycles, and probabilistic detection of rapid ¹⁴C increases, the work
identified four intervals of reduced solar activity, two periods of weakening and subsequent strengthening of the eleven-year solar cycle, and four candidate particle events in 14, 553, 675, and 954 CE.
Building on this approach, we present several newly measured, high-precision annual ¹⁴C datasets derived from tree-ring samples processed independently in multiple laboratories and originating from different geographic regions. The records cover a key interval in the late Middle Holocene, shortly after the Mid-Holocene Optimum. Despite differences in site conditions, tree species, and laboratory procedures, all datasets show a synchronous and abrupt radiocarbon increase within a narrow time window. The consistency and magnitude of this signal suggest a large-scale atmospheric forcing rather than local environmental or analytical effects, indicating a possible solar origin.
To evaluate the significance of this excursion, we compared the new records with available ¹⁴C datasets, including both annually resolved and lower-resolution archives. The results indicate that the observed increase is rare within the Holocene background variability and comparable to other short-lived radiocarbon anomalies. We further investigated potential production mechanisms using the open-source carbon box model ticktack to reconstruct atmospheric ¹⁴C production. Two scenarios were tested: (1) a one-year production pulse representing an impulsive SEP-type event, and (2) a multi-year production increase reflecting enhanced cosmic-ray flux due to reduced solar magnetic
shielding. Preliminary simulations show that both scenarios can reproduce the amplitude and temporal structure of the observed signal within model uncertainties.
Future work will apply a fully three-dimensional carbon transport model to better resolve atmospheric mixing and regional offsets, enabling discrimination between competing production scenarios. These results provide new constraints on short-term solar variability during the late Middle Holocene and contribute to understanding extreme solar behaviour in the pre-instrumental era.

Co-author list:
Bao Yang (2), Fusa Miyake (3), Irina Panyushkina (4), Jente Joosten (1), Vivian Kroon (1), Håkan Grudd (5), David Brown (6), Ronny Friedrich (7), Michael Dee (1)

(1) Centre for Isotope Research, University of Groningen, Groningen, Netherlands
(2) School of Geography and Ocean Science, Nanjing University, Nanjing, People’s Republic of China
(3) Institute for Space‑Earth Environmental Research, Nagoya University, Nagoya, Japan
(4) Laboratory of Tree‑Ring Research, University of Arizona, Tucson, USA
(5) Swedish Polar Research Secretariat, Abisko Scientific Research Station, Abisko, Sweden
(6) School of Natural and Built Environment, The Queen’s University Belfast, Belfast, UK
(7) Curt‑Engelhorn‑Center for Archaeometry (CEZA), Mannheim, Germany

Speaker: Jian Wang (University of Groningen, NL)

14:25 Bridging the gap between extreme and modern SEP events: high-precision 14C analysis of the 1279 CE event

Cosmogenic nuclides used to detect past solar energetic particle (SEP) events are tree-ring $^{14}$C, and ice-core $^{10}$Be, and $^{36}$Cl. These nuclides serve as key proxies for reconstructing SEP events. To date, multiple extreme SEP events, including the 774 CE event, have been identified from these cosmogenic nuclide records. The magnitudes of these events are estimated to be several tens of times larger than the largest SEP events observed during the modern instrumental era, underscoring the importance of investigating their occurrence characteristics for space weather risk assessment. In recent years, substantial progress has been made in identifying extreme SEP events during the Holocene, particularly those comparable in scale to the 774 CE event. However, investigation of intermediate-size events that bridge the gap between proxy-detected extreme events and those observed in the modern era remains limited, mainly due to analytical uncertainties in cosmogenic nuclide measurements.
In this study, we focus on the 1279 CE event, one of the smallest candidate events reported from tree-ring $^{14}$C records. Although previous studies reported statistically significant increases in Δ$^{14}$C associated with this event, the annual increases were relatively small, ranging from approximately 2 to 5‰, and its origin remains under debate (Brehm et al. 2021; Miyahara et al. 2022; Scifo et al. 2024). We conducted high-precision Δ$^{14}$C measurements on tree-ring samples from Japan and the Altai region covering the period around 1279 CE. While we did not detect a statistically significant single-year increase in Δ$^{14}$C, we identified a significant multi-year increase. Our results suggest that this Δ$^{14}$C enhancement is consistent with both an extreme SEP event and variations in galactic cosmic ray flux. These findings indicate that distinguishing intermediate-size SEP events from background variations of galactic cosmic rays will be a key challenge in future studies. To address this issue, multi-proxy approaches incorporating tree-ring $^{14}$C records from multiple regions, as well as ice-core cosmogenic nuclide records, will be essential.

Co-author list:
A. J. Timothy Jull (2,3), Katsuhiko Kimura (4), Mihaly Molnár (3), Toru Moriya (5), Vladimir Myglan (6), Irina P. Panyushkina (7), Andrea Scifo (8), Mirei Takeyama (5), Fuyuki Tokanai (5), Ilya Usoskin (9,1), Lukas Wacker (10)

(1) Institute for Space‑Earth Environmental Research, Nagoya University, Nagoya 464‑8601, Japan
(2) Department of Geosciences, University of Arizona, Tucson AZ 85721, USA
(3) Isotope Climatology and Environmental Research Centre, Institute for Nuclear Research, Debrecen 4032, Hungary
(4) Fukushima University, Fukushima, Japan
(5) Yamagata University, Yamagata, Japan
(6) Siberian Federal University, Krasnoyarsk 660041, Russia
(7) Laboratory of Tree‑Ring Research, University of Arizona, Tucson AZ 85721, USA
(8) Centre for Isotope Research, University of Groningen, Groningen, The Netherlands
(9) Space Physics and Astronomy Research Unit and Sodankylä Geophysical Observatory, University of Oulu, 90014 Oulu, Finland
(10) Laboratory for Ion Beam Physics, ETH Zürich, Zürich 8093, Switzerland

Speaker: Fusa Miyake (Nagoya U., JP)

14:45 Assessing the Strength and Timing of Extreme Solar Particle Events from Δ¹⁴C Data via SOCOL:14C-Ex Climate-Chemistry Model

Extreme solar particle events (ESPEs) are caused by rare, enormously intense solar eruptions and can produce globally detectable spikes in tree-ring radiocarbon ($^{14}$C), known as Miyake events, which serve as precise chronological tie-points and indicators of extreme solar activity. After production, radiocarbon is subjected to the complex carbon cycle, including large- scale atmospheric transport, which is crucially important for fast and strong Miyake events with highly inhomogeneous 14C production. In this study, we apply the 3D dynamical climate-chemistry model SOCOL:14C-Ex, which simulates atmospheric $^{14}$C production and transport with high temporal and spatial resolution, to quantify extreme solar particle events. Response curves of Δ$^{14}$C to a reference ESPE (100 × GLE #69) were computed for different event dates in both hemispheres and used to analyse Miyake events under varying background conditions. Seven strong events over the past 14 millennia (AD 993, AD 774, 664 BC, 5260 BC, 5411 BC, 7177 BC, and 12351 BC) were analysed by fitting the reference curves to the available annual 14C data, identifying the most probable values and confidence intervals of their strength (relative to the reference ESPE) and timing. By applying corrections for the geomagnetic and atmospheric (CO$_2$) factors, the strengths of the corresponding ESPEs were reassessed.

Speaker: Sergey Koldobskiy (University of Oulu)

14:57 New millennial scale reconstruction of solar magnetic activity at annual resolution from cosmogenic proxies

Long-term solar magnetic variability governs the space climate conditions. These variations also modulate the galactic cosmic ray influx reaching Earth and subsequently regulate the production of cosmogenic isotopes in the Earth's atmosphere. By harnessing the multi-millennial records of these radio-isotope proxies archived in various natural terrestrial reservoirs, such as tree rings and ice cores, it is possible to reconstruct past solar magnetic activity predating the telescopic era.
However, existing regression-based reconstruction methods often yield negative sunspot numbers during low solar activity phases, which are unphysical.
To address this, we have recently developed a Monte‑Carlo inversion framework consisting of a sequence of physics‑based forward models, supplemented by an approximate Bayesian computation-based posterior selection, to infer the most plausible temporal evolution of solar magnetic parameters, including solar modulation potential, open solar flux, and sunspot numbers. Our approach produces physically consistent, uncertainty‑quantified multi-millennial reconstructions of annually resolved sunspot numbers.
The reconstruction shows excellent agreement with direct observations during the telescopic era. We further identify epochs of extreme solar activity, such as grand solar minima, and examine their statistical properties.
These results offer valuable insights into long-term solar variability and provide improved constraints for long-term solar dynamo modelling. The annual-scale reconstructions are also directly usable for solar irradiance estimation, terrestrial climate modelling, and studies of long‑term Sun-Earth coupling.

Speaker: Chitradeep Saha (University of Reading, UK)

15:09 High-latitude evidence for a rapid 14C onset of the ~660 BC event

Rapid increases in atmospheric radiocarbon ($^{14}$C), known as Miyake events, have been identified across multiple time periods, with Solar Proton Events (SPEs) considered the most probable cause. Among these, the ~660 BC event stands out due to its apparently prolonged rise time compared to other confirmed events such as AD 774–775 and AD 993–994, prompting hypotheses ranging from double SPEs to encounters with interstellar gas clouds. In this study, we present new annual and subannual $^{14}$C measurements from Scots pine (Pinus sylvestris) tree rings from Finnish Lapland (66.8°N), covering the periods 680–650 BC and 670–655 BC, respectively.
Our results reveal that the $^{14}$C signal begins rising in the latewood of 665 BC, reaching near-full intensity by 664 BC, with a peak around 662–661 BC at an amplitude of approximately 15‰. This timing aligns closely with independent high-latitude measurements from Yamal, Russia, but precedes the rise observed at lower-latitude sites in Germany, Japan, and the Altai region. The earlier and more pronounced signal at high latitudes mirrors patterns documented for the AD 774 and AD 993 events, pointing to a consistent mechanism involving either direct tropospheric $^{14}$C production at polar latitudes or a rapid component of stratosphere-to-troposphere air mass transfer in polar regions.
Carbon cycle box model simulations reproduce the observed peak shape well. Importantly, the model yields nearly identical fits for scenarios involving either a single or double SPE, indicating that the box model approach alone cannot resolve whether one or multiple production events caused the ~660 BC anomaly. Qualitative comparison of the high-latitude peak shapes of the ~660 BC and AD 774 events reveals striking similarity, which argues against the need for multiple SPEs or more exotic causes, and instead supports a scenario where the observed peak shape arises from the interplay of initial $^{14}$C production and atmospheric transport processes. These findings underscore the necessity of developing latitude-resolved, dynamic carbon cycle models capable of capturing the rapid polar transfer of stratospheric CO$_2$ into the troposphere and its subsequent dilution into lower-latitude air masses.
Based on: Park J, Uusitalo J, Hong W, Park G, Sung K, Hackman T, Helama S, Mäkinen H, Nöjd P and Oinonen M (2026). Early 14C i
ncrease in high-latitude trees at 665–664 BC. Radiocarbon, in press. doi:10.1017/RDC.2026.10195

Co-authors:
Junghun Park (1), Wan Hong (1), Gyujun Park (1), Kilho Sung (3), Thomas Hackman (4), Samuli Helama (5), Harri Mäkinen (6), Pekka Nöjd (6), Markku Oinonen (2)
(1) Korea Institute of Geoscience and Mineral Resources, Geoanalysis Center, Republic of Korea
(2) Finnish Museum of Natural History, University of Helsinki, Helsinki, Finland
(3) GNS Science, Gracefield, Lower Hutt, New Zealand
(4) Department of Physics, University of Helsinki, Helsinki, Finland
(5) Natural Resources Institute Finland, Rovaniemi, Finland
(6) Natural Resources Institute Finland, Helsinki, Finland

Speaker: Joonas Uusitalo (Helsinki U., FI)

15:21 Radiocarbon variations in tree rings of Patagonia around SPE1956: what can we learn about the extreme solar eruption?

Instrumental observations of extreme solar eruptions are short, restricting their linkages to paleoevents (e.g. Miyake events) derived from cosmogenic $^{14}$C, $^{36}$Cl and $^{10}$Be isotopes of ice cores and tree rings. This constrains estimates of their long-term frequency and probability. The strongest solar proton event (SPE) recorded by ground-level enhancement occurred on 23 February 1956 (GLE #5), during the maximum phase of the strongest solar cycle #19 (1954–1964). Through recent reanalysis of historical data Usoskin et al. (2020) confirmed that SPE1956 ranks among the hardest-energy SPEs ever recorded. The event produced an extraordinary peak in neutron-monitor count rate as 5117–5276% above the Galactic Cosmic Ray (GCR) background sustained for nearly one hour. Despite this intensity, simulated annual production rates of $^{10}$Be and $^{14}$C of ice cores show only ≈5% increase above the GCR background. For comparison, the corresponding increase in the 775 CE Miyake event is about 210-270% (Mekhaldi et al. 2015).
The SPE1956 event occurred during the nuclear testing era, when natural concentration of cosmogenic isotopes, except 10Be, has been severely affected by the thermal neutrons ejected by aboveground nuclear explosions in the late 1950s and early 1960s. These neutrons reacted with atmospheric nitrogen producing anthropogenic $^{14}$C (bomb $^{14}$C). Because bomb-produced $^{14}$C was injected primarily in the Northern Hemisphere, interhemispheric transport and gradient delayed the $^{14}$C peak in the Southern Hemisphere (SH) by 1–2 years. We analyzed tree-ring radiocarbon from the SH Zone 1-2 around the time of SPE1956 to identify the impact of $^{14}$C bomb emissions on the SPE1956 spike signature in tree rings. Annually resolved Δ$^{14}$C series from two tree species: Lenga beech and Chile pine were developed for the interval 1952-1961 from the Tierra del Fuego National Park, Patagonia. The growing season for both trees is about five months, from October to March. The beech series shows a significantly positive offset of 16.6 ‰+0.9‰ (total χ² $_{\nu=9}$ =12.47 or reduced χ² =1.39) relatively to the pine series. According to monthly atmospheric Δ$^{14}$C data for the SH Zone1-2, the increase of bomb $^{14}$C begins gradually in June 1955, only 7 months prior to the SPE1956 event. It then increases rapidly and stabilizes briefly at ~200 ‰ in 1960-1962 before soaring to 680 ‰ by 1969. The tree-ring Δ$^{14}$C changes over 15‰ from 1955 to 1956 closely following the structure of SH zone 1-2 atmospheric Δ$^{14}$C record. We discuss the 14C production rate derived from $^{14}$C tree-ring signature of the SPE1956 event and the seven-month missed opportunity for integrating instrumental observations with the proxy records of GCR intensity.
References:
Usoskin et al. 2020. Revisited reference solar proton event of 23 February 1956: Assessment of the cosmogenic-isotope method sensitivity to extreme solar events. JGR 125, e2020JA027921.
Mekhaldi et al. 2015. Multiradionuclide evidence for the solar origin of the cosmic-ray events of AD 774/5 and 993/4. Nat Commun 6, 8611.

Speaker: Irina Panyushkina (University of Arizona, US)

15:33 Are signals from historical supernovae observable in the radiocarbon record?

Rapid spikes observed in the tree-ring $^{14}$C record are caused by extreme solar proton storms or high-energetic particles events. Six of these “Miyake” events have been confirmed with 10Be in ice cores at 774 CE, 993 CE, 664 BCE, 5259 BCE, 7176 BCE, and 12450 BCE. There are also a number of $^{14}$C excursions attributed to solar effects that are not yet confirmed by other cosmogenic nuclides. There are other smaller-magnitude spikes in the $^{14}$C record in tree rings were detected but their origin is not explained or associated with known cosmic events. It has been previously noted that a rapid increase in production rate of cosmogenic isotopes could also be related to a supernova explosion (SN) or gamma-ray bursts (GRB). Modeling of the effect of energetic photons from an SN on the Earth's atmosphere suggested the possibility to measure it through production of cosmogenic isotopes (Menjo et al. 2005; Pavlov et al. 2013). These ideas have already been explored by several different studies (Damon et al. 1995; Menjo et al. 2005; Dee et al. 2023). We studied $^{14}$C content of tree rings from five locations during the historic supernova explosion SN1181 documented by Chinese and Japanese astronomers as a "guest star" in the Cassiopeia constellation to investigate its possible impact on the $^{14}$C variance in the atmosphere and the cosmogenic isotope production rate. Three new annually resolved AMS radiocarbon series were developed for the 1170-1190 CE interval from hemlock collected in Alaska, white spruce from the Columbia Icefields of Alberta, and larch from Indigirka River in eastern Siberia. We found no clear signature in the radiocarbon content of tree rings to response to the historic supernova explosion. We also compared our results to two previous records over the same time frame, from sequoia in California and a European oak chronology (Eastoe et al. 2019, Brehm et al. 2021). The ∆$^{14}$C signal did not show any significant and consistent increase around 1181 CE. Also, modeling of the $^{14}$C production rate calculated with a carbon-cycle 22-box model revealed no significant increase around 1181 CE. The inconsistent signature of the SN1181 event observed for $^{14}$C in tree rings gives a similar response as the radiocarbon pattern previously observed for the SN1054 Crab Nebula supernova event in several studies.

Co-author list:
Irina P. Panyushkina (3), Mihály Molnár (2), Támas Varga (2,4), Valerie Livina (5), Gregory Wiles (6), Nicholas Wiesenberg (6), Robert J. S. Wilson (7)
(2) Isotope Climatology and Environmental Research Centre, Institute for Nuclear Research, Debrecen, Hungary
(3) Laboratory of Tree‑Ring Research, University of Arizona, Tucson, AZ, USA
(4) Max‑Planck‑Institut für Biogeochemie, Jena, Germany
(5) National Physical Laboratory, Teddington, Middlesex, UK
(6) College of Wooster, Wooster, Ohio, USA
(7) University of St Andrews, UK

Speaker: Timothy Jull (University of Arizona, US)

15:45 → 16:05 Coffee break

16:05 → 17:09 3.3 Historical proxy (chair Delores Knipp)

Convener: Hisashi Hayakawa (Nagoya U., JP)

16:05 Solar flare effects in retrospect

Solar flare effects (Sfe) are rapid variations in the Earth’s magnetic field. They are the response to an enhancement of the amount of radiation during Solar flare events.
The Carrington’s observations in 1859 related geomagnetic variations with solar radiations. They represented the first direct evidence of the connection between the Sun’s activity and the Earth’s environment. Since then, much progress has been made in the understanding Sun-Earth system. The interest for the effects of large flare events has increased with their capability to put technological systems in danger.
In this presentation, I will review the state-of-the-art of the Sfe, and the development and advances made in the knowledge concerning Sfe phenomena. First, I will offer a historical approach with a comprehensive description of which are the main characteristics of Sfe. This also includes specific topics like the puzzling reversed-Sfe or the night-time Sfe. I will stress the role played by the Service of Rapid Magnetic variations (SRMV) in Sfe knowledge and popularization. This will be followed by a discussion of the main current limiting factors in the process of detection and the proposed ways to overcome challenges such as creating an automatic detection method. I will clarify some aspects related to the geo-effectiveness of the solar flares producing magnetic disturbances. Also, I will provide an overview of the temporal evolution of the electric currents producing Sfe. The importance of key subjects such as the dynamic aspects of Sfe will be developed later. Finally, estimations of the size of large flares using historical ionospheric and magnetic data will be reviewed.

Speaker: Juan José Curto Subirats (Observatori de l’Ebre, ES)

16:25 Improving our knowledge of the solar diameter: a new look involving the leptocline

Among all the fundamental solar parameters, mass, surface gravity, temperature, luminosity..., all well inventoried for several years in reference books, solar diameter is still a controversial issue, both its true value and any possible temporal variations. The most exact value of the solar diameter is of importance, as it serves as an astronomical standard. Changing its absolute value can, for example, significantly alter the absolute diameter of stars, since the diameter of all stars is defined relative to that of the Sun (it may result an impact on the inferred stellar structures - though the density for instance). Considerable efforts to measure the solar diameter(s) have been made during the second half of the XXth century, involving dedicated space instruments, as well as eclipse observations of high precision. Modern 3-D solar theories show that the leptocline (inside the near sub-solar surface -NSSL-, a shallow and sharp rotational shear layer in the top around 8 Mm), can be modelized and is in rather good agreement with helioseismic observations deduced, for instance, from the HMI experiment on board the Solar Dynamics Observatory (SDO) NASA satellite. The role of the leptocline in causing solar diameter(s) variations is now well documented. In this presentation, we attempt to shed further light on the matter. After defining what a solar diameter refers to -photospheric, seismic, acoustic…-, we will give an overview of what we know today about changes in the Sun’s diameter over time. A quick aside will be made on diameter variations with heliographic latitude. We will address the role played by the leptocline in shaping the solar sub-surfacing layers, hence enables us to interpret the different solar diameters. We propose a fully updated glossary with meaning of solar diameters in use today in an attempt to reach a consensus on this still somewhat disputed subject. To conclude, this new look on such modern measurements of the Sun’s global changes gives a new way for peering into the solar interior, mainly to better understand the subsurface fields which play an important role in the implementation of solar cycles.

Speaker: Jean-Pierre Rozelot (Université Côte d’Azur, FR)

16:45 Solar cycles over a millennial timescale: Reconstruction and statistics

Solar cyclic activity was discovered in the 19$^\textrm{th}$ century and traced back to 1610 CE through directly observed sunspots. Using indirect cosmogenic proxy data, such as $^{14}$C in tree trunks and $^{10}$Be in ice cores, it is possible to reconstruct long-term solar activity back for several millennia, but individual cycles were not readily resolved. Thanks to the recent breakthrough in the precision of $^{14}$C measurements, cyclic solar activity can now be reconstructed over millennia using precise annually resolved radiocarbon data.
Here, we present a detailed reconstruction of solar cyclic activity, via annual sunspot numbers (SNs), during the first millennium CE. This period includes one extreme solar event occurring in 774 CE and one Grand solar minimum covering 650—730 CE. A total of 91 solar cycles were identified for the first millennium CE, including 26, 24, and 41 cycles, which were well, reasonably, and poorly defined, respectively.
We perform a statistical analysis of the reconstructed cycles, focusing on the distributions of cycle lengths, amplitudes, and shapes (Waldmeier’s relations). We also discuss the reliability of the solar cycle definition during grand solar minima. The statistical results are compared with those for other periods of known solar cyclic activity

Speaker: Ilya Usoskin (Oulu U., FI)

16:57 When do observations become historical?

The 21$^\textrm{st}$ century has brought us many new and exciting groundbreaking facilities such as Daniel K. Inouye Solar Telescope (DKIST), Solar Dynamics Observatory (SDO), and Solar Orbiter (SO) with more on the horizon such as Next Generation Ground based Solar Observing Network (ngGONG) and PHOtospheric Magnetograph Imager (PHOMI) for upcoming NOAA SpaceWeather Geostationary (SWGEO) program satellites. While these new facilities bring excitement and new opportunities to unravel the mystery of our sun, they risk accelerating issues with facilities that they replace and the data they produce. The biggest risk lies with 20$^\textrm{th}$ century data but is present in more recent observations as well. These risks include not only being underutilized but also lost to time, appearing too old for most researchers to use but too modern for historians to care about. However, they o er unique perspectives that haven’t been observed with the latest instrumentation such as the modern maximum period (solar cycles 15-23), the flares of August 1972, and the Great Sunspot Group of 1947. This talk will focus on current efforts to preserve crucial historical data products, their uses, and ask the question of when, “do observations become historical?”. Before finishing with a discussion on the fact that all these new 21$^\textrm{st}$ century facilities will eventually become historical as the field advances.

Speaker: Alexander Pevtsov (US National Solar Observatory, US)

17:09 → 18:13 3.4 Predictability in space climate (chair Delores Knipp)

Convener: Timo Asikainen (Oulu U., FI)

17:09 Solar effects on El Niño and its potential predictability

The tropical Pacific variability significantly affects the global weather and climate from annual to interdecadal timescales. The El Niño Southern–Oscillation (ENSO) in this region has a direct association with extreme weather precipitation and climate anomalies across the world. Many studies have been shown that the tropical Pacific has statistically significant responses to the solar variability, especially the 11-year solar cycle. However, the response patterns are quite diverse or even contradicting, such as some studies demonstrated that the solar-induced responses in the tropical Pacific resemble ENSO, some others showed that it’s not ENSO-like but weak warming. Despite some possible mechanisms are proposed to explain the associated response, the influence of the 11-year solar cycle in the tropical Pacific is an ongoing debated topic. In my talk, I will give a general review of studies on solar impacts on ENSO and tropical Pacific climate, highlights key uncertainties and proposed mechanisms. Finally, I will talk about the potential contribution of solar variability to regional climate predictability.

Speaker: Wenjuan Huo (GEOMAR, DE)

17:29 Can the EEP direct effect on mesospheric ozone change the global atmospheric dynamics?

Recent studies have revealed important advances in understanding how the direct effects of energetic electron precipitation (EEP) on mesospheric ozone influence atmospheric dynamics (Zúñiga López et al., 2022). These findings show that EEP can significantly affect mesospheric temperature, wave breaking and refraction, and consequently atmospheric winds and circulation. However, the magnitude of EEP’s dynamical impact in the mesosphere remains insufficiently quantified.
To isolate the direct mesospheric effects of EEP, we employ the Whole Atmosphere Community Climate Model (WACCM) in specified-dynamics (SD) mode throughout the stratosphere, following the configuration of Zúñiga López et al. (2022). By comparing simulations using five different >30 keV EEP input datasets to a base run without EEP, we assess the robustness of EEP-induced changes. We evaluate the resulting mesospheric response in NOx, HOx, ozone, temperature, winds, wave activity, and transport, alongside its dependence and influence on the strength of the polar vortex.

Speaker: Hilde Nesse (University of Bergen, NO)

17:49 Predicting geomagnetic activity in the ascending and declining phases of the solar cycle

Most predictions of space climate, that is, the long-term behavior of the solar-terrestrial environment, have focused on forecasting the 11-year sunspot cycle. Geomagnetic activity, on the other hand, has mainly been predicted in shorter, space weather timescales of up to days to weeks. Using a 180-year composite aa index, we aim to predict here the temporal behavior of geomagnetic activity over the last 16 solar cycles. By identifying activity peaks in the ascending and declining phases of the cycle and an activity minimum between the two, we represent each aa cycle with two triangular peaks. The large-scale features of the aa cycle depicted by the model are related to changes in the occurrence of coronal mass ejections and high-speed solar wind streams which drive geomagnetic activity. Using past aa and sunspot observations, as well as a recent sunspot cycle prediction model, we find interesting relationships for the predictability of the aa peak amplitudes and timings, which suggest intrinsic differences between even and odd cycles and give strong support to the so-called Gnevyshev-Ohl rule ordering of cycles to even-odd cycle pairs. Finally, we attempt to hindcast each past aa cycle, including the ongoing cycle 25, while also estimating the prediction uncertainty using a leave-one-out cross-validation methodology. Prediction of a new cycle is made at the time of aa minimum at the start of the cycle, which occurs typically a few months after the sunspot minimum.

Speaker: Timo Qvick (Oulu U., FI)

18:01 Space climate effects in the stratosphere as a source of improved winter weather predictability

Space climate affects not only the magnetosphere and ionosphere, but also the middle atmosphere, including the mesosphere (50–80 km) and stratosphere (15–50 km). Variations in solar radiation and precipitating energetic particles (EPP) influence atmospheric composition, particularly ozone, which plays a central role in the atmospheric radiative balance through its absorption of shortwave and longwave radiation and its emission in the longwave range.
During polar winter, in the absence of solar radiation, the lifetime of NOx compounds produced by EPP increases substantially. Under conditions of enhanced EPP activity, wintertime circulation transports larger amounts of NOx downward into the lower mesosphere and upper stratosphere, where these compounds catalytically destroy ozone. The resulting ozone changes alter the local radiative balance and thereby affect temperature and eventually strengthen the polar vortex. The associated anomalies can then propagate downward and occasionally influence the troposphere.
This downward coupling is particularly relevant in winter, when stratosphere–troposphere interactions are strongest, especially in connection with sudden stratospheric warming (SSW) events, which are known to affect weather over large parts of the Northern Hemisphere. The occurrence of these events was found to be suppressed during periods of high EPP. Because the stratosphere is generally less chaotic than the troposphere, improved understanding of space-climate forcing, and especially better predictability of solar forcing, may offer a pathway to improved subseasonal predictability of winter weather in the troposphere. This highlights the societal relevance of space climate. For instance, we have recently shown that Finland’s electricity consumption and wind power generation correlate with geomagnetic activity during winters with favorable equatorial stratospheric winds.

Speaker: Mikhail Vokhmianin (Oulu U., FI)

19:00 → 21:00 Social dinner (Restaurang Nautical, Hamngatan 2)

Menu 1 (Regular menu + pescatarians + no mushroom diet + gluten and lactose-free):
1. Seared scallops, ratatouille vinaigrette, Arenkha caviar, cauliflower crème and mussel foam with a glass of wine/soft drink
2. Pike perch (AX), browned butter sauce, fennel, cucumber and trout roe with a glass of wine/soft drink
3. Crème Brûlée with fresh berries with coffee/tea

Menu 2 (for vegetarians):
1. Vichyssoise, brioche, leek, seaweed roe and dill with a glass of wine/soft drink
2. Salt-baked root celery, potato dumplings, creamed cabbage, porcini butter, cranberries and vegetarian red wine jus with a glass of wine/soft drink
3. Crème Brûlée with fresh berries with coffee/tea

Menu 3 (no fish or seafood):
1. Vichyssoise, brioche, leek, seaweed roe and dill with a glass of wine/soft drink
2. Roe deer inside round (SWE), truffle butter, Madeira jus, cabbage, potato and Jerusalem artichoke gratin with a glass of wine/soft drink
3. Crème Brûlée with fresh berries with coffee/tea

Please note that, in addition to the drinks included with dinner, you may also order extra beverages during the meal at your own expense.

Friday 12 June

09:00 → 10:40 2.4 Magnetosphere-ionosphere-thermosphere and space climate hazards (chair Nandita Srivastava)

Convener: Eija Tanskanen (Oulu U., FI)

09:00 The Critical Influence of Cold Plasma Density for Rapid Radiation Belt Dynamics during Intense Geomagnetic Storm Events

Very Low Frequency (VLF) whistler-mode chorus and hiss emissions are pervasive features of the Earth’s magnetosphere, playing a critical role in controlling the dynamics of the outer Van Allen radiation belt. Through interactions with trapped electrons, these waves drive both upper-atmosphere ionization and the energization of relativistic electrons, posing significant space weather hazards to satellite infrastructure and astronauts. While current wave models generally correlate wave amplitude enhancements with rising geomagnetic activity, this approach is insufficient to explain the fine-scale dynamics observed during storm events. Notably, historical analyses reveal that geomagnetic storms produce highly variable outcomes, with geosynchronous fluxes increasing in only 53% of events, while decreasing or remaining unchanged in others. This variability suggests the presence of critical, unaccounted factors that govern the global efficiency of wave-particle interactions and determine the predominance of scattering versus acceleration regimes. Key factors recently identified to affect this efficiency include: (i) the dependence of chorus frequency on latitude, which lowers the electron scattering resonance; (ii) the latitudinal distribution of wave amplitude and high-latitude wave extent; (iii) the distribution of wave normal angles, specifically the influence of oblique whistler populations; and (iv) background plasma characteristics, particularly the coupling of cold plasma density with hot electron populations. In this study, show the importance of the integrated approach (which includes a comprehensive combination of the local parameters) to estimations of wave-particle interactions efficiency in the radiation belts and present a survey of MeV electron pitch angle and energy quasi-linear diffusion rates driven by chorus and hiss waves as a function of L-shell, local time, and AE index. Our model accounts for the local electron plasma frequency to gyrofrequency ratio (fpe/fce), chorus wave frequency, and resonant wave amplitude. We demonstrate that during disturbed periods, the fpe/fce ratio strongly decreases in the night sector. This leads to faster electron loss, but also significantly faster electron energization in two distinct regions: just above the plasmapause and at L = 3.5– 5.5. We conclude that spatiotemporal variations of fpe/fce with the AE index shape the evolution of electron energization in the outer belt, leading to extremely short time scales for quasi-linear MeV electron acceleration, in agreement with Van Allen Probes observations during the intense geomagnetic storms.

Speaker: Dr Oleksiy Agapitov (California Berkeley U., US)

09:20 Insights into the Electrodynamic Properties of Meso-Scale Auroral Morphologies Through Self-Supervised Learning

At high-latitude regions on the Earth, auroral displays exhibit strong spatiotemporal variability yet fall into broad morphological classifications. Studies have shown that different types of aurora can exhibit distinct particle precipitation energies and fluxes, convection electric field configurations, and preferential occurrence rates across different levels of geomagnetic activity. The variable electrodynamic forcing imposed by these structures can generate plasma density irregularities, temperature variations, and ground magnetic perturbations that can pose risks to communication systems and infrastructure sensitive to geomagnetically induced currents. Traditionally, meso-scale auroral classes are identified through visual inspection of all-sky imager (ASI) data. However, this approach requires manually sorting through millions of images introducing inherent uncertainties due to subjective and limited categorizations, especially when multiple classes may be present. Furthermore, the determination of electrodynamic properties and impacts necessitate acquiring data from multiple co-located instruments. To address these challenges, we employ a self-supervised contrastive learning algorithm to systematically extract characteristic features from the all sky imager data located at Poker Flat, Alaska during intervals of increased geomagnetic activity. We identify occurrence rates of different labels with respect to ground magnetic field signatures to investigate their association with substorm phases. We use measurements from the Poker Flat Incoherent Scatter Radar to characterize the electric fields, average energies, and energy fluxes associated with each morphological class and quantify the temperature variations in the Ionosphere. We compare our clustering methodology with classifications reported in the literature and present a statistical analysis of the resulting labels, establishing a framework for characterizing and assessing the geoeffectiveness of distinct auroral forms.

Speaker: Dr Dogacan Ozturk (Alaska Fairbanks U., US)

09:40 Role of Pc5 pulsations and KH instability in the Sun-Earth coupling during extreme geomagnetic storms

The energy from the Sun emitted in a large variety of frequencies is powering the polar areas, but the energy is not distributed evenly over the latitudes. We found out that over 40% of the available energy dissipates to the 2° wide band around 67° CGM when the area between 56-76° CGM is considered. During winter months the largest amount of energy dissipates to a narrower latitudinal range than in summer. Magnetic fluctuations are the most frequent about 5° more north, compared to the most energetic substorm impact area. These substorm-like magnetic features at Bear Island do not appear to distribute significant amounts of energy. Substorms in the southern Finland are relatively infrequent and furthermore bring as well quite small amounts of solar wind originated energy. However, the substorms reaching these latitudes are intense and long, resulting in relatively energetic substorm intervals.
According to our study, the energy starts to leak through the magnetopause during extreme solar storms while during the typical Sun-Earth coupling conditions much of the energy circulate through the magnetotail. We study the role of Pc5 pulsations and Kelvin-Helmholz instability in the leakage process during space hazards and compare storms originated from complex and simple solar active regions. The 19th January 2026 event is shown as an example of geomagnetic storms with the very rapid start of the storm, measured by the equatorial magnetometers. The characteristics of this “Carrigton-type of event start” is compared with the other known extreme geomagnetic storms.

Speaker: Prof. Eija Tanskanen (FI)

09:52 Revisiting the Tsyganenko 1989 Magnetosphere Model and its Extension to Storm Conditions

he first of a successful line of semi-empirical magnetospheric models was created by Tsyganenko (1989), henceforth referred to as the TSY models. TSY89 captured the structure of the magnetosphere well for low to mid geomagnetic disturbances and was parametrised simply using the planetary Kp index. For this reason, TSY89 is still widely used today when modelling the magnetosphere under similar conditions, despite the subsequent development of more advanced and complex TSY models. This model is particularly helpful when we model cutoff suppressions over historical geomagnetic storms before satellite measurements. TSY89 was initially parametrised for Kp values of 0, 1, 2, 3, 4, and ≥5. To extend the model to higher levels of disturbance and mitigate the problem of the Kp saturations, Boberg et al. (1995) introduced a novel method in which the ring current parameter in TSY89 was modulated based on the Dst index. This simple modification relied on a linear fit between the ring current parameter in TSY89 and the mean Dst for each Kp level. This “Boberg extension” has since seen wide application in numerous studies. The linear fit describing the Boberg extension is heavily reliant on the fitted parameters within TSY89. A reparametrisation in 1996, coinciding with the development of the TSY96 model, led to significantly different ring current parameters within the TSY89 model. This fact, however, has not been widely documented, and the original 1995 Boberg extension continues to be used despite the update to the TSY89 model.
In this work, the TSY89 model is revisited, and spacecraft from 1966 to 2025 are collected to enable a complete reparametrisation of TSY89, the most recent version of which used spacecraft data between 1966 to 1986, using the expanded dataset. The Boberg extension is re-evaluated for the 1989, 1996, and new 2026 versions of TSY89 by repeating notable prior studies that employed the Boberg extension, namely transmission function computations for the October 1989 solar energetic particle (SEP) events and cutoff latitude calculations for SAMPEX during the November 1992 SEP events. A comparison of the effectiveness of the respective Boberg extensions is then conducted. It is found that all models perform well under low geomagnetic disturbance conditions, but that the 1995 and 2026 versions perform significantly better during more extreme disturbances. We show preliminary calculations for the cutoff suppressions over the most extreme geomagnetic storms such as the Carrington storm, the February 1872 storm, and the May 1921 storm. We also try to estimate the cutoff rigidity suppressions for the theoretically greatest geomagnetic storm.

Speaker: Nicholas Larsen (Nagoya U., JP)

10:04 Evolution of open magnetic flux during substorms: the effects of dipole tilt angle

The solar wind, a stream of charged particles emanating from the Sun, interacts with Earth’s magnetosphere. This interaction creates space weather phenomena such as geomagnetic storms, substorms, and auroras. Space weather is driven by solar wind and the interplanetary magnetic field (IMF) which drive ionospheric electric currents in the Earth’s magnetosphere and ionosphere. It is well-known that geomagnetic activity is stronger during equinoxes compared to solstices, an effect known as the semiannual variation of geomagnetic activity. There is a long-standing debate on the causes of semiannual variation. One of the suggested hypotheses is that the dipole tilt angle ψ modulates the dayside reconnection rate. Here we perform the first large-scale statistical study to test this hypothesis. We identified about 1300 isolated substorms in 2010-2023 and used the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) measurements to determine the open magnetic flux variations and estimates of the dayside reconnection rate during these substorm events. We find a greater amount of open flux is stored in the tail prior to the substorm expansion phase during low ψ than during large ψ. This is due to a dipole tilt dependence of the dayside reconnection rate, and possibly another mechanism operating in the magnetotail. These two effects contribute to the semiannual variation of geomagnetic activity.

Speaker: Achuthan Nair (Oulu U., FI)

10:16 Hemispheric and dawn-dusk asymmetries of Kelvin-Helmholtz waves driven by dipole tilt and IMF By

Along with magnetic reconnection, Kelvin-Helmholtz (KH) waves are the main mechanisms controlling the solar wind-magnetosphere interaction. Kelvin-Helmholtz waves have been shown to be important for plasma transport into the magnetosphere, enabled by secondary processes such as reconnection, diffusion and wave-particle interactions. Here we use magnetohydrodynamical (MHD) simulations for studying how the Kelvin-Helmholtz instability (KHI) is modulated by the dipole tilt angle and IMF By. We find that KH wave activity on the magnetopause maximizes in the winter hemisphere and at dawn sector for positive IMF By. These asymmetries of KHI are caused by asymmetric draping of interplanetary magnetic field (IMF) in the magnetosheath and dawn-dusk asymmetry in magnetic reconnection, creating a broader boundary layer slowing the growth of KHI at dusk for positive By. These results are important for understanding field-aligned currents generated by the KH vortices and their effects on geomagnetic activity and its seasonal variation.

Speaker: Dr Lauri Holappa (Oulu U., FI)

10:28 Long-term observations of mid-latitude thermospheric winds

Multi-year observations of the thermospheric wind are available at many mid latitude locations. NCAR and other institutes have been operating ground based Fabry Perot interferometer for nighttime O 630 nm airglow Doppler remote sensing to monitor thermospheric winds. Thermospheric winds are affected by solar and geomagnetic activities, as well as atmospheric tides from lower atmosphere. Long term observation can help understand solar cycle effect and other long-term variations in the atmosphere. We will compare observations from Boulder Colorado and other locations with NCAR TIEGCM to study the long-term trends in the mid latitude thermospheric winds. Other NCAR model simulation will also be explored. The goal is to characterize the effects from above (solar and geomagnetic) and below (atmospheric).

Speaker: Dr Qian Wu (NCAR, US)

10:40 → 11:10 Coffee break

11:10 → 11:40 Solar Wind Dynamic Pressure Pulses and their influence on Solar Wind-Geospace Coupling and the Designation of Superstorms

Speaker: Prof. Delores Knipp (Colorado Boulder U., US)

11:40 → 12:48 3.2 Climate and atmospheric effects (chair Hilde Nesse and Roelf Du Toit Strauss)

Convener: Tatiana Egorova (PMOD/WRC)

11:40 Energetic particle precipitation impacts on the atmosphere and climate in idealised time-slice simulations

Energetic particle precipitation (EPP) provides an important pathway for space weather to influence the middle and lower atmosphere, yet its role in atmospheric variability and predictability remains uncertain. While EPP-driven production of NOx and subsequent ozone depletion can affect stratospheric dynamics and surface climate, observational constraints are limited: reanalysis products rely on indirect proxies, and separating EPP signals from internal variability is challenging. This motivates a modeling-based approach to isolate mechanisms and assess their robustness.
Here, we investigate EPP impacts on atmospheric chemistry, dynamics, and surface climate using long-term time-slice simulations with the SOCOLv4.0 chemistry–climate model. Simulations are performed under pre-industrial conditions, with EPP forcings based on the strong 2003 "Halloween storms" and weak 2008 events. Consistent with established understanding, EPP enhances polar NOx, depletes ozone, and modifies stratospheric and tropospheric circulation through coupled radiative–dynamical feedbacks. However, the sign of the polar vortex and surface response depends on both hemisphere and the timing of strong EPP events.
In addition, we identify a delayed pathway: mid-latitude ozone depletion caused by post-winter transport of EPP-produced NOx, which can precondition the stratosphere and modulate the following winter’s polar vortex, at times opposing the canonical EPP response. This points to a seasonal memory effect and raises the question of how robust such mechanisms are under realistic conditions, particularly during multiyear periods of enhanced EPP associated with solar cycle maxima, and whether they contribute meaningfully to climate predictability.

Speaker: Dr Timofei Sukhodolov (PMOD/WRC, CH)

12:00 Energetic particle influence on polar vortex revealed by 300-year long climate model simulations

Many past studies based on climate reanalysis data have strongly indicated that energetic electron precipitation (EEP) from space into the polar atmosphere leads to mesospheric and stratospheric ozone loss. This in turn affects radiative balance in the atmosphere and leads to thermal changes, which enhance the stratospheric polar vortex.
Here we study the EEP influence on the atmosphere and climate system using the SOCOL3-MPIOM chemistry-climate model. We run idealized 300-year long timeslice simulations with (experiment run) and without (control run) EEP forcing both constrained by same constant boundary conditions. The control run captures the internal variability of the climate system without EEP forcing, while the experiment run depicts the variability of the climate system when it is forced with EEP. The EEP forcing employs a parameterization to represent the influx of NOx molecules through the model top created by low-energy auroral precipitation. We also include the direct ionization produced by EEP evaluated from a new data composite based on POES satellite observations. The model is repetitively forced each year throughout the entire simulation with the EEP forcing observed during winter 2003/2004.
We discuss here the modeled response of the polar vortex and its downward coupling to energetic electron precipitation. Specifically, we show that a significant strengthening of the polar vortex and associated ground climate variability is seen only when the background atmospheric state is optimal to allow for a dynamical response to take place. The optimal state is identified using a new method called optimal modulation analysis, which indicates that the polar vortex response to EEP requires enhanced planetary wave activity equatorward of the polar vortex.

Speaker: Prof. Timo Asikainen (Oulu U., FI)

12:12 11-year solar cycle shapes the north-south contrast of summer precipitation in China

Solar forcing significantly influences the variability of monsoon patterns. However, the connection between decadal variation of monsoon precipitation patterns and solar cycles remains ambiguous. This study investigates the influence of the 11-year solar cycle on East Asian summer monsoon precipitation from 1958 to 2020, revealing that the decadal-scale pattern of opposing rainfall anomalies between northern and southern China is driven by a solar-coupled mechanism linked to the East Asia/Pacific teleconnection. During high solar activity years, stratospheric ozone heating in response to enhanced solar radiation generates a warm anomaly in the tropical and subtropical lower stratosphere, which triggers anomalous convection in the troposphere, reinforces the EAP teleconnection, and shifts the rain belt northward. This warm anomaly also strengthens midlatitude westerlies in the upper troposphere and lower stratosphere, aiding the downward propagation of the solar signal and further amplifying the EAP pattern. As a result, the EAP teleconnection channels solar influence into the EASM region, producing drought in southern China and flooding in the north. These findings propose a stratosphere–troposphere coupling mechanism through which solar variability shapes spatial precipitation patterns, offering new insights into the decadal variability of monsoon rainfall.

Speaker: Prof. Liang Zhao (Institute of Atmospheric Physics, Chinese Academy of Sciences, CN)

12:24 Atmospheric and Climate Impacts of an Extreme Solar Particle Event Under the Reconstructed Laschamps Geomagnetic Field

Solar particle events (SPEs) are short-lived bursts of high-energy particles from the solar atmosphere and are important drivers of changes of the atmospheric chemistry. While most SPEs are relatively weak and have limited environmental impacts, evidence from cosmogenic radionuclides indicates that much stronger events have occurred in the past. The effects of such extreme SPEs depend strongly on the configuration of the Earth’s geomagnetic field, which modulates the penetration of energetic particles into the atmosphere. Periods of geomagnetic excursions, such as the Laschamps event (~41 ka), are characterized by a substantially weakened and reconfigured geomagnetic field, potentially enhancing the atmospheric impact of SPEs. Here, we investigate the effects of an extreme SPE under the reconstructed Laschamps geomagnetic field using the atmosphere–ocean–chemistry–climate model SOCOLv4. In contrast to previous idealized simulations assuming the absence of a geomagnetic field, the Laschamps reconstruction provides a spatially complex and physically consistent representation of geomagnetic shielding. We focus on the resulting changes in atmospheric composition, including NOx and HOx production, and their impact on ozone from the mesosphere to the surface. In addition, we examine the associated changes in atmospheric temperature, dynamics, and circulation.

Speaker: Dr Pavle Arsenović (BOKU, AT)

12:36 Volcanic modulation of Beryllium-10 atmospheric transport

Cosmogenic $^{10}$Be isotope is an important proxy for past solar activity that can be measured from natural archives such as ice cores. It is mostly produced in the stratosphere and its atmospheric lifetime until the deposition to the surface depends on different transport processes. Notably, $^{10}$Be isotopes may attach to aerosol particles, where these are abundant, and subsequently follow their trajectories, leading to stronger sedimentation. This effect would yet be massively increased by strong volcanic eruptions, which has been proposed as a major complication in the interpretation of $^{10}$Be proxy records. In our study, we test this hypothesis by employing the state-of-the-art aerosol-chemistry-climate model SOCOL-AERv2-Be that has a full $^{10}$Be atmospheric cycle, in- cluding its attachment to aerosol particles. We isolate the effects of sedimentation by comparing simulations with and without it for the $^{10}$Be tracer. In these simulations we examine the long-term climatological effects of a background aerosol layer on the $^{10}$Be distribution in the atmosphere and the resulting deposition maps. In another set of simulations we specifically focus on the influence of the enhanced stratospheric aerosol layer after volcanic events. The results are compared with ice core data from polar stations.

Speaker: Mr Andrin Jörimann (PMOD/WRC, CH)

12:48 → 13:48 Lunch

Minced beef (1st option) or roasted celeriac (2nd option) with pepper sauce, broccoli, kale, and roasted potatoes
Including water, salad, bread, butter and coffee/tea

13:48 → 15:03 3.2 Climate and atmospheric effects (chair Hilde Nesse and Roelf Du Toit Strauss)

Convener: Tatiana Egorova (PMOD/WRC)

13:48 Galactic cosmic rays, clouds, and atmospheric dynamics: a reinterpretation of the connection

At polar latitudes small changes in cloud amount, temperature and pressures correlate with changes in the solar wind electric field. These changes occur on a timescale of days, and in the absence of significant changes in in-situ ion production. They can be understood as resulting from changes in the ionosphere-earth current density, JZ, in the global electric circuit modulating space charge and cloud microphysical processes as it flows through stratiform clouds with low aerosol concentration. We hypothesize that other small changes in day-to-day and decadal cloud cover and storm vorticity at middle and high geomagnetic latitude, that correlate with JZ changes which are due to solar proton events, energetic electron precipitation, and galactic cosmic ray changes, can also be understood in the same way. This is a reinterpretation of the previous explanation of cosmic ray – cloud correlations. Observational evidence for the correlations, and for the theory for the relevant microphysical processes in clean remote mid-high latitude marine air are reviewed. The accumulation of space charge in the form of concentrations of negative ions just below cloud bases provides a favorable environment for ultrafine aerosol particles to become charged and grow, resulting in enhanced concentrations of cloud condensation nuclei (CCN). After days of processing, the CCN transported up into the cloud shift the droplet size distributions to smaller sizes and reduce precipitation. These cloud changes also affect vorticity of winter cyclones and the blocking of circulation at mid-latitudes. The tropospheric dynamical responses are in conjunction with stratospheric dynamical changes due to other solar and terrestrial inputs.

Speaker: Prof. Brian Tinsley (Texas U., US)

14:00 Importance of Interactive Chlorine Chemistry for Modeling Cosmogenic 36-Cl

Cosmogenic radionuclide $^{36}$Cl serves as an important proxy for reconstructing past solar variability, geomagnetic field intensity, and atmospheric circulation. However, global modeling of $^{36}$Cl remains challenging, particularly due to uncertainties in representing stratospheric chlorine processes. In this study, we implement a new configuration of the chemistry-climate model SOCOL-AERv2 that includes an explicit, fully interactive stratospheric chlorine cycle for $^{36}$Cl. We conduct multi-decadal simulations covering the pre-nuclear era (1894–1941), when atmospheric $^{36}$Cl was produced exclusively by cosmic rays. Two modeling approaches are evaluated: one in which $^{36}$Cl participates in the full interactive chlorine chemistry, and another in which it is represented as a passive gaseous tracer transported without chemical feedbacks. Our results indicate that both configurations produce very similar large-scale distributions, transport pathways, and deposition patterns of $^{36}$Cl. This suggests that detailed interactive chlorine chemistry exerts only a minor influence on the global behaviour of cosmogenic $^{36}$Cl. Consequently, simplified transport-only representations may be sufficient for many applications, enabling more computationally efficient simulations.

Speaker: Dr Kseniia Golubenko (Oulu U., FI)

14:13 Energetic electron precipitation weakens the southern polar vortex via chlorine deactivation

Electrons from the Earth’s magnetosphere precipitate into the polar upper atmosphere. There, energec electron precipitaon (EEP) forms reacve NOx and HOx compounds which, for example, catalycally destroy ozone. In the northern hemisphere EEP and its effect on ozone modulate the temperature so that the westerly winds around the polar region, the so-called polar vortex, strengthen during mid-winter. However, in the southern hemisphere the EEP seems to weaken the polar vortex during spring. Earlier studies have shown that EEP-NOx also deacvates reacve chlorine compounds in the southern hemisphere, which complicates the overall effect of EEP on ozone and, thus, polar vortex. We here examine the EEP effect on chemical and dynamical features of southern middle atmosphere using the POES satellite measurements of EEP and the Aura satellite measurements and the ERA5 reanalysis data of atmospheric variables. We show that EEP destroy ozone during mid-winter but increases it during spring when EEP-NOx has descended close to the middle stratosphere. We also confirm that EEP weakens the springme polar vortex in the southern hemisphere. Moreover, we show that this EEP effect on the southern polar vortex correlates with the amount of CFC compounds in the atmosphere. This finding implies that the EEP effect depends firmly on chlorine deacvaon in the southern hemisphere.

Speaker: Dr Antti Salminen (Oulu U., FI)

14:25 Atmospheric dynamical responses to geomagnetic storms: from case studies to statistical analyses

Precipitation of energetic particles (often referred to as EPP) from solar or magnetospheric origin into the earth polar atmosphere has long been recognized as an important forcing of the chemical budget of the middle atmosphere. Its impact on atmospheric trace gases such as ozone, nitrogen and hydrogen oxides (NO$_\mathrm{x}$ and HO$_\mathrm{x}$), and chlorine species, has been identified. More controversial is the potential feedback of the EPP-induced ozone losses on the dynamics of the middle atmosphere and of the troposphere, and ultimately on surface climate.
Re-analyses such as ERA-40, MERRA-2, and JRA-55 have been widely used for the research on EPP-induced climate signals of wind and temperature. The advancement of reanalysis datasets, undertaken by multiple meteorological agencies worldwide under the framework of the Atmospheric Processes and Their Role in Climate (APARC) project, has extended the upper boundary of atmospheric reanalyses from the stratosphere into the mesosphere. The ISSI team ‘Dynamical signatures of energetic particle precipitation in atmospheric re-analyses’ primarily re-assesses the ozone, temperature and potential dynamical signatures of EPP from the mesosphere down to the troposphere in existing, state-of-the-art global atmospheric re- analyses. Meanwhile, complementary case study simulations with WACCM-X, WACCM-D and SIC help quantifying the impact of extreme geomagnetic activities on atmospheric composition, thermal structure, and circulation. In this presentation, we report published and preliminary results from the team, spanning tidal variability, compositional changes, and their associated dynamical responses across multiple atmospheric layers, based on model simulations and reanalysis datasets.

Speaker: Dr Jia Jia (FMI, FI)

14:38 Polar mesospheric NOx transport in 21st century WACCM-D simulations

The transport of mesospheric nitrogen oxides (NO$_\mathrm{x}$), produced by energetic electron precipitation (EEP), down to stratosphere during polar winter is expected to increase in the future due to acceleration of mean meridional circulation. In stratosphere, the transported NO$_\mathrm{x}$ is known to contribute to the catalytic ozone losses in late winter and early spring.
We use Whole Atmosphere Community Climate Model with expanded D-region ion chemistry package (WACCM-D) to study the 21st century polar circulation and transport of mesospheric NO$_\mathrm{x}$ during polar winter. Introduction of D-region ion chemistry reactions in the place of standard parameterization enhances the mesospheric production of NO$_\mathrm{x}$.

Speaker: Dr Niilo Kalakoski (FMI, FI)

14:51 Association of solar activity with atmospheric circulation: Long-term analysis based on Hess-Brezowsky catalogue of circulation types

Whether there is association between solar activity and tropospheric circulation, is still an open research question. Various characteristics of circulation have been analyzed in this respect, including its composites and correlation / regression fields, teleconnections (such as the North Atlantic Oscillation), position and duration of blocking events, and frequency of circulation types. Although many studies suggest that associations between solar activity and circulation are significant particularly in the European-North Atlantic sector, there are many unknowns, such as the temporal stability of such associations and the degree to what they may be (or may be not) mistaken for a response to other forcings, most notably to sudden stratospheric warmings.
Here we present an analysis, which is based on Hess-Brezowsky (H-B) catalogue of circulation types. In the catalogue, every day is assigned to one of 29 circulation types according to the airflow direction, position of cyclones and anticyclones, (anti)cyclonicity of airflow, etc., over central Europe. Two versions of the H-B catalogue are utilized as a source of data on tropospheric circulation: original subjective (starting from 1881), and modified objective (starting from 1851). The description of atmospheric circulation in terms of the H-B catalogue has the advantages of covering a much longer time span than what full-input atmospheric reanalyses allow, and of being independent of surface-input atmospheric reanalyses, which – although also cover periods extending into the 19th century – do not incorporate potential solar effects coming from above via interactions with stratospheric ozone.
The analysis of frequencies of H-B circulation types conditioned by levels of solar activity (expressed as sunspot numbers) and/or phases of solar cycle shows a significant association between solar activity and tropospheric circulation over central Europe. Under low solar activity, westerly types tend to be less frequent, and northerly and easterly types more frequent. Anticyclonic situations occur more frequently under low solar activity, compensating for the reduced frequency of cyclonic types. However, the relationships between solar activity and frequencies of H-B types change over time. They are particularly significant since the 1940s and in the early part of the analyzed period shortly after the middle of the 19th century. These periods of significant associations coincide with high solar activity cycles. This suggests that it is the level of solar activity, rather than the phase of the solar cycle, that plays a crucial role in the relationship between solar activity and tropospheric circulation. That is, weak solar cycles do not allow the association with tropospheric circulation to develop. Taken from a different perspective, the weakening or even lack of the solar-to-circulation association, which is observed in the early 20th century, does not mean that what we observe as an association is in fact random (which some studies seem to suggest); instead, it is an impact of solar cycles being weak.

Speaker: Prof. Radan Huth (Charles U., CZ)

15:03 → 15:23 Award ceremony and the end of SC10