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Dipolarization Fronts: Tangential Discontinuities? On the Spatial Range of Validity of the MHD Jump Conditions
Author(s) -
Schmid D.,
Volwerk M.,
Plaschke F.,
Nakamura R.,
Baumjohann W.,
Wang G.Q.,
Wu M.Y.,
Zhang T.L.
Publication year - 2019
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2019ja027189
Subject(s) - classification of discontinuities , magnetohydrodynamics , plasma , physics , magnetic field , discontinuity (linguistics) , distributed file system , jump , flux (metallurgy) , mechanics , computational physics , geophysics , materials science , mathematics , mathematical analysis , computer security , quantum mechanics , computer science , metallurgy
Magnetotail dipolarization fronts (DFs) are referred as the sharp increase of the northward magnetic field component, embedded in bursts of fast earthward moving plasma flows, so called bursty bulk flows. Earlier studies often considered DFs as tangential discontinuities (TDs), which can be understood as thin vertical current layers of earthward moving flux tubes, so called dipolarzing flux bundles (DFBs), which separate the ambient plasma sheet plasma from the low entropy plasma within the DFB. Here we present a statistical study of 23 DFs observed by the Magnetospheric Multiscale mission during 2017 and 2018 when the apogee was at 25 R E in the magnetotail. We perform a test of the Walén relation to distinguish whether the observed DFs have rather a TD or rotational discontinuity character and evaluate the plasma flow across the DFs in detail. The results show that on MHD large scales, all 23 DFs can be considered as TD like, but sometimes may have a significant normal plasma flow across it: for 16 events (∼70 % ), the plasma flows mainly tangential to the DFs, while for seven events (∼30 % ), the plasma flows mainly across the DFs. Based on the findings present in this study, we further hypothesize that the DF structure becomes more distorted and unstable in a (locally) more dipolarized background magnetic field region, which may additionally facilitate the plasma flow across the front.