Open AccessSubstorm ion injections: Geosynchronous observations and test particle orbits in three‐dimensional dynamic MHD fields
Author(s) -
Birn J.,
Thomsen M. F.,
Borovsky J. E.,
Reeves G. D.,
McComas D. J.,
Belian R. D.,
Hesse M.
Publication year - 1997
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/96ja03032
Subject(s) - substorm , physics , field line , ion , test particle , particle acceleration , atomic physics , flux (metallurgy) , magnetosphere , plasmoid , pitch angle , electric field , particle (ecology) , geophysics , magnetohydrodynamics , magnetic reconnection , magnetic field , acceleration , classical mechanics , materials science , geology , oceanography , quantum mechanics , metallurgy
We investigate particle acceleration and the flux increases associated with substorm particle injections using geosynchronous observations and test proton orbits in the dynamic fields of a three‐dimensional MHD simulation of neutral line formation and dipolarization in the magnetotail. The energetic particle flux changes obtained from the test particle orbits agree well with observations that demonstrate rapid ion flux increases at energies above ∼20 keV but little change at lower energies. The “injection region” inferred from the test particles not only has a sharp earthward boundary (the usual injection boundary) but also a sharp but ragged tailward boundary. The earthward portion of enhanced ion flux can be traced to the enhanced cross‐tail electric field associated with the collapse and dipolarization of the inner tail, whereas the tailward edge is closely associated with the near‐Earth x‐type neutral line. Because of the rapid earthward motion of accelerated ions away from the neutral line, this boundary is displaced earthward to where the energetic ions become more adiabatie in the stronger dipolar field. Lower‐energy ions are not affected by cross‐tail acceleration in the strong E y fields because their earthward E × B drift dominates the cross‐tail drift, except very close to the neutral line.