On the Radial and Longitudinal Variation of a Magnetic Cloud: ACE, Wind, ARTEMIS and Juno Observations
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On the Radial and Longitudinal Variation of a Magnetic Cloud: ACE, Wind, ARTEMIS and Juno Observations Emma E. Davies1 · Robert J. Forsyth1 · Simon W. Good2 · Emilia K. J. Kilpua2
Received: 23 January 2020 / Accepted: 24 September 2020 © The Author(s) 2020
Abstract We present observations of the same magnetic cloud made near Earth by the Advance Composition Explorer (ACE), Wind, and the Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun (ARTEMIS) mission comprising the Time History of Events and Macroscale Interactions during Substorms (THEMIS) B and THEMIS C spacecraft, and later by Juno at a distance of 1.2 AU. The spacecraft were close to radial alignment throughout the event, with a longitudinal separation of 3.6◦ between Juno and the spacecraft near Earth. The magnetic cloud likely originated from a filament eruption on 22 October 2011 at 00:05 UT, and caused a strong geomagnetic storm at Earth commencing on 24 October. Observations of the magnetic cloud at each spacecraft have been analysed using minimum variance analysis and two flux rope fitting models, Lundquist and Gold–Hoyle, to give the orientation of the flux rope axis. We explore the effect different trailing edge boundaries have on the results of each analysis method, and find a clear difference between the orientations of the flux rope axis at the near-Earth spacecraft and Juno, independent of the analysis method. The axial magnetic field strength and the radial width of the flux rope are calculated using both observations and fitting parameters and This article belongs to the Topical Collection: Towards Future Research on Space Weather Drivers Guest Editors: Hebe Cremades and Teresa Nieves-Chinchilla Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11207-020-01714-z) contains supplementary material, which is available to authorized users.
B E.E. Davies
[email protected] R.J. Forsyth [email protected] S.W. Good [email protected] E.K.J. Kilpua [email protected]
1
The Blackett Laboratory, Imperial College London, London, UK
2
Department of Physics, University of Helsinki, Helsinki, Finland
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their relationship with heliocentric distance is investigated. Differences in results between the near-Earth spacecraft and Juno are attributed not only to the radial separation, but to the small longitudinal separation which resulted in a surprisingly large difference in the in situ observations between the spacecraft. This case study demonstrates the utility of Juno cruise data as a new opportunity to study magnetic clouds beyond 1 AU, and the need for caution in future radial alignment studies. Keywords Coronal mass ejections, interplanetary · Magnetic clouds · Multi-spacecraft observations · Radial evolution · Longitudinal variation · Juno
1. Introduction Interplanetary coronal mass ejections (ICMEs: e.g. Kilpua, Koskinen, and Pulkkinen, 2017) are large-scale structures of plasma and magneti
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