Issue |
A&A
Volume 679, November 2023
Solar Orbiter First Results (Nominal Mission Phase)
|
|
---|---|---|
Article Number | A106 | |
Number of page(s) | 20 | |
Section | The Sun and the Heliosphere | |
DOI | https://doi.org/10.1051/0004-6361/202347006 | |
Published online | 29 November 2023 |
Backstreaming ions at a high Mach number interplanetary shock
Solar Orbiter measurements during the nominal mission phase
1
Swedish Institute of Space Physics, Uppsala, Sweden
e-mail: andrew.dimmock@irfu.se
2
Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva, Israel
3
Space and Plasma Physics, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
4
Imperial College London, London, UK
5
Swedish Defence Research Agency, Stockholm, Sweden
6
University of Turku, Turku, Finland
7
Departamento de Ciencias Espaciales, Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria, Ciudad de México, Mexico
8
Mullard Space Science Laboratory, University College London, London, UK
9
Institute of Experimental and Applied Physics, Kiel University, 24118 Kiel, Germany
Received:
25
May
2023
Accepted:
5
September
2023
Context. Solar Orbiter, a mission developed by the European Space Agency, explores in situ plasma across the inner heliosphere while providing remote-sensing observations of the Sun. The mission aims to study the solar wind, but also transient structures such as interplanetary coronal mass ejections and stream interaction regions. These structures often contain a leading shock wave that can differ from other plasma shock waves, such as those around planets. Importantly, the Mach number of these interplanetary shocks is typically low (1–3) compared to planetary bow shocks and most astrophysical shocks. However, our shock survey revealed that on 30 October 2021, Solar Orbiter measured a shock with an Alfvén Mach number above 6, which can be considered high in this context.
Aims. Our study examines particle observations for the 30 October 2021 shock. The particles provide clear evidence of ion reflection up to several minutes upstream of the shock. Additionally, the magnetic and electric field observations contain complex electromagnetic structures near the shock, and we aim to investigate how they are connected to ion dynamics. The main goal of this study is to advance our understanding of the complex coupling between particles and the shock structure in high Mach number regimes of interplanetary shocks.
Methods. We used observations of magnetic and electric fields, probe-spacecraft potential, and thermal and energetic particles to characterize the structure of the shock front and particle dynamics. Furthermore, ion velocity distribution functions were used to study reflected ions and their coupling to the shock. To determine shock parameters and study waves, we used several methods, including cold plasma theory, singular-value decomposition, minimum variance analysis, and shock Rankine-Hugoniot relations. To support the analysis and interpretation of the experimental data, test-particle analysis, and hybrid particle in-cell simulations were used.
Results. The ion velocity distribution functions show clear evidence of particle reflection in the form of backstreaming ions several minutes upstream. The shock structure has complex features at the ramp and whistler precursors. The backstreaming ions may be modulated by the complex shock structure, and the whistler waves are likely driven by gyrating ions in the foot. Supra-thermal ions up to 20 keV were observed, but shock-accelerated particles with energies above this were not.
Key words: Sun: coronal mass ejections (CMEs) / solar wind / shock waves / plasmas / waves / instabilities
© The Authors 2023
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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