Speaker
Description
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