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In Which Magnetotail Hemisphere is a Satellite? Problems Using in Situ Magnetic Field Data
Author(s) -
De Spiegeleer A.,
Hamrin M.,
Gunell H.,
Pitkänen T.,
Chong S.
Publication year - 2021
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2020ja028923
Subject(s) - magnetic field , physics , spacecraft , plasma sheet , northern hemisphere , current sheet , geophysics , southern hemisphere , satellite , magnetosphere , astrophysics , computational physics , atmospheric sciences , astronomy , magnetohydrodynamics , quantum mechanics
In Earth's magnetotail plasma sheet, the sunward‐tailward B x 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 B x > 0 ( B x < 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 B x is likely due to such a dent, and not to the spacecraft moving across the neutral sheet.