TY - JOUR

T1 - Signatures of Nonideal Plasma Evolution During Substorms Obtained by Mining Multimission Magnetometer Data

AU - Sitnov, M. I.

AU - Stephens, G. K.

AU - Tsyganenko, N. A.

AU - Miyashita, Y.

AU - Merkin, V. G.

AU - Motoba, T.

AU - Ohtani, S.

AU - Genestreti, K. J.

PY - 2019/11/1

Y1 - 2019/11/1

N2 - Substorm-type evolution of the Earth's magnetosphere is investigated by mining more than two decades (1995-2017) of spaceborne magnetometer data from multiple missions including the first two years (2016-2017) of the Magnetospheric MultiScale mission. This investigation reveals interesting features of plasma evolution distinct from ideal magnetohydrodynamics (MHD) behavior: X-lines, thin current sheets, and regions with the tailward gradient of the equatorial magnetic field B-z. X-lines are found to form mainly beyond 20 R-E, but for strong driving, with the solar wind electric field exceeding similar to 5mV/m, they may come closer. For substorms with weaker driving, X-lines may be preceded by redistribution of the magnetic flux in the tailward B-z gradient regions, similar to the magnetic flux release instability discovered earlier in PIC and MHD simulations as a precursor mechanism of the reconnection onset. Current sheets in the growth phase may be as thin as 0.2 R-E, comparable to the thermal ions gyroradius, and at the same time, as long as 15 R-E. Such an aspect ratio is inconsistent with the isotropic force balance for observed magnetic field configurations. These findings can help resolve kinetic mechanisms of substorm dipolarizations and adjust kinetic generalizations of global MHD models of the magnetosphere. They can also guide and complement microscale analysis of nonideal effects.

AB - Substorm-type evolution of the Earth's magnetosphere is investigated by mining more than two decades (1995-2017) of spaceborne magnetometer data from multiple missions including the first two years (2016-2017) of the Magnetospheric MultiScale mission. This investigation reveals interesting features of plasma evolution distinct from ideal magnetohydrodynamics (MHD) behavior: X-lines, thin current sheets, and regions with the tailward gradient of the equatorial magnetic field B-z. X-lines are found to form mainly beyond 20 R-E, but for strong driving, with the solar wind electric field exceeding similar to 5mV/m, they may come closer. For substorms with weaker driving, X-lines may be preceded by redistribution of the magnetic flux in the tailward B-z gradient regions, similar to the magnetic flux release instability discovered earlier in PIC and MHD simulations as a precursor mechanism of the reconnection onset. Current sheets in the growth phase may be as thin as 0.2 R-E, comparable to the thermal ions gyroradius, and at the same time, as long as 15 R-E. Such an aspect ratio is inconsistent with the isotropic force balance for observed magnetic field configurations. These findings can help resolve kinetic mechanisms of substorm dipolarizations and adjust kinetic generalizations of global MHD models of the magnetosphere. They can also guide and complement microscale analysis of nonideal effects.

KW - B hump

KW - data mining

KW - magnetic reconnection

KW - magnetotail

KW - substorm

KW - thin current sheet

KW - Bz hump

KW - FIELD

KW - MAGNETIC RECONNECTION

KW - B-z hump

KW - MHD

KW - MAGNETOTAIL EQUILIBRIA

KW - DIPOLARIZATION FRONTS

KW - ENERGY-CONVERSION

KW - SOLAR-WIND

KW - GROWTH-PHASE

KW - STEADY MAGNETOSPHERIC CONVECTION

KW - THIN CURRENT SHEETS

UR - http://www.scopus.com/inward/record.url?scp=85074835751&partnerID=8YFLogxK

UR - http://www.mendeley.com/research/signatures-nonideal-plasma-evolution-during-substorms-obtained-mining-multimission-magnetometer-data

U2 - 10.1029/2019JA027037

DO - 10.1029/2019JA027037

M3 - Article

AN - SCOPUS:85074835751

VL - 124

SP - 8427

EP - 8456

JO - Journal of Geophysical Research: Biogeosciences

JF - Journal of Geophysical Research: Biogeosciences

SN - 0148-0227

IS - 11

ER -