Speaker
Description
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