University of Oulu

De Spiegeleer, A., Hamrin, M., Gunell, H., Pitkänen, T., & Chong, S. (2021). In which magnetotail hemisphere is a satellite? Problems using in situ magnetic field data. Journal of Geophysical Research: Space Physics, 126, e2020JA028923.

In which magnetotail hemisphere is a satellite? : problems using in situ magnetic field data

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Author: De Spiegeleer, A.1; Hamrin, M.1; Gunell, H.1;
Organizations: 1Department of Physics, Umeå University, Umeå, Sweden
2Space Physics and Astronomy Research Unit, University of Oulu, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.1 MB)
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Language: English
Published: American Geophysical Union, 2021
Publish Date: 2021-10-19


In Earth‘s magnetotail plasma sheet, the sunward-tailward Bx component of the magnetic field is often used to separate the region above and below the cross-tail current sheet. Using a three-dimensional magneto-hydrodynamic simulation, we show that high-speed flows do not only affect the north-south magnetic field component (causing dipolarization fronts), but also the sunward-tailward component via the formation of a magnetic dent. This dent is such that, in the Northern Hemisphere, the magnetic field is tailward while in the Southern Hemisphere, it is earthward. This is opposite to the expected signatures where Bx > 0 (Bx < 0) above (below) the neutral sheet. Therefore, the direction of the magnetic field cannot always be used to identify in which hemisphere an in situ spacecraft is located. In addition, the cross-tail currents associated with the dent is different from the currents in a tail without a dent. From the simulation, we suggest that the observation of a dawnward current and a tailward magnetic tension force, possibly together with an increase in the plasma beta, may indicate the presence of a magnetic dent. To exemplify, we also present data of a high-speed flow observed by the Cluster mission, and we show that the changing sign of Bx is likely due to such a dent, and not to the spacecraft moving across the neutral sheet.

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Series: Journal of geophysical research. Space physics
ISSN: 2169-9380
ISSN-E: 2169-9402
ISSN-L: 2169-9380
Volume: 126
Issue: 2
Article number: e2020JA028923
DOI: 10.1029/2020JA028923
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: A. De Spiegeleer, M. Hamrin, H. Gunell, and T. Pitkanen. are supported by the Swedish National Space Agency grant numbers 105/14, 271/14, 108/18, and 118/17. The authors would like to thank M. Kuznetsova for the recommending the simulation. This work was carried out using the SWMF and BATS-R-US tools developed at the University of Michigan's Center for Space Environment Modeling (CSEM).
Copyright information: © 2021. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.