Radial evolution of the April 2020 stealth coronal mass ejection between 0.8 and 1 AU. Comparison of Forbush decreases at Solar Orbiter and near the Earth


Johan L. Freiherr von Forstner, Christian-Albrechts-Universität zu Kiel
Mateja Dumbovic, University of Zagreb
Christian Mostl, Austrian Academy of Sciences
Jingnan Guo, University of Science and Technology of China
Athanasios Papaioannou, National Observatory of Athens
Robert Elftmann, Christian-Albrechts-Universität zu Kiel
Zigong Xu, Christian-Albrechts-Universität zu Kiel
Jan Christoph Terasa, Christian-Albrechts-Universität zu Kiel
Alexander Kollhoff, Christian-Albrechts-Universität zu Kiel
Robert F. Wimmer-Schweingruber, Christian-Albrechts-Universität zu Kiel
Javier Rodriguez-Pacheco, Universidad de Alcalá
Andreas J. Weiss, Austrian Academy of Sciences
Jurgen Hinterreiter, Austrian Academy of Sciences
Tanja Amerstorfer, Austrian Academy of Sciences
Maike Bauer, Austrian Academy of Sciences
Anatoly V. Belov, Russian Academy of Sciences (IZMIRAN)
Maria A. Abunina, Russian Academy of Sciences (IZMIRAN)
Timothy Horbury, Imperial College London
Emma E. Davies, Imperial College London
Helen O'Brien, Imperial College London
Robert C. Allen, Johns Hopkins University
G. Bruce Andrews, Johns Hopkins University
Lars Berger, Christian-Albrechts-Universität zu Kiel
Sebastian Boden, Christian-Albrechts-Universität zu Kiel
Ignacio Cernuda Cangas, Universidad de Alcalá
Sandra Eldrum, Christian-Albrechts-Universität zu Kiel
Francisco Espinosa Lara, Universidad de Alcalá
Raul Gomez Herrero, Universidad de Alcalá
John R. Hayes, Johns Hopkins University
George C. Ho, Johns Hopkins University
Shrinivasrao R. Kulkarni, Christian-Albrechts-Universität zu Kiel
W. Jeffrey Lees, Johns Hopkins University
Cesar Martin, Christian-Albrechts-Universität zu Kiel
Glenn M. Mason, Johns Hopkins University
Daniel Pacheco, Christian-Albrechts-Universität zu Kiel
Manuel Prieto Mateo, Universidad de Alcalá
Ali Ravanbakhsh, Christian-Albrechts-Universität zu Kiel
Oscar Rodriguez Polo, Universidad de Alcalá
Sebastian Sanchez Prieto, Universidad de Alcalá
Charles E. Schlemm, Johns Hopkins University
Helmut Seifert, Johns Hopkins University
Kush Tyagi, University of Colorado, Boulder
Mahesh Yedla, Christian-Albrechts-Universität zu Kiel


Aims. We present observations of the first coronal mass ejection (CME) observed by the Solar Orbiter spacecraft on April 19, 2020 and the associated Forbush decrease (FD) measured by the High Energy Telescope (HET). This CME is a multi-spacecraft event that was also seen near Earth the following day.

Methods. We highlight the capabilities of the HET for observing small short-term variations of the galactic cosmic ray count rate using its single detector counters. We applied the analytical ForbMod model to the FD measurements to reproduce the Forbush decrease at both locations. Input parameters for the model were derived from both in situ and remote-sensing observations of the CME.

Results. The very slow (∼350 km s−1) stealth CME caused an FD with an amplitude of 3% in the low-energy cosmic ray measurements at HET and 2% in a comparable channel of the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on board the Lunar Reconnaissance Orbiter, as well as a 1% decrease in neutron monitor measurements. Significant differences are observed in the expansion behavior of the CME at different locations, which may be related to influence of the following high speed solar wind stream. Under certain assumptions, ForbMod is able to reproduce the observed FDs in low-energy cosmic ray measurements from HET as well as CRaTER, however, with the same input parameters, the results do not agree with the FD amplitudes at higher energies measured by neutron monitors on Earth. We study these discrepancies and provide possible explanations.

Conclusions. This study highlights the notion that the novel measurements of Solar Orbiter can be coordinated with observations from other spacecraft to improve our understanding of space weather in the inner heliosphere. Multi-spacecraft observations combined with data-based modeling are also essential for understanding the propagation and evolution of CMEs, in addition to their space weather impacts.

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Astronomy & Astrophysics


The European Southern Observatory

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