Physics – Plasma Physics
Scientific paper
May 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998jgr...103.9235b&link_type=abstract
Journal of Geophysical Research, Volume 103, Issue A5, p. 9235-9248
Physics
Plasma Physics
54
Magnetospheric Physics: Energetic Particles, Precipitating, Magnetospheric Physics: Magnetospheric Configuration And Dynamics, Magnetospheric Physics: Storms And Substorms, Space Plasma Physics: Numerical Simulation Studies
Scientific paper
We investigate electron acceleration and the flux increases associated with energetic electron injections on the basis of geosynchronous observations and test-electron orbits in the dynamic fields of a three-dimensional MHD simulation of neutral line formation and dipolarization in the magnetotail. This complements an earlier investigation of test protons [Birn et al., 1997b]. In the present paper we consider equatorial orbits only, using the gyrocenter drift approximation. It turns out that this approximation is valid for electrons prior to and during the flux rises observed in the near tail region of the model at all energies considered (~100 eV to 1 MeV). The test particle model reproduces major observed characteristics: a fast flux rise, comparable to that of the ions, and the existence of five categories of dispersionless events, typical for observations at different local times. They consist of dispersionless injections of ions or electrons without accompanying injections of the other species, delayed electron injections and delayed ion injections, and simultaneous two-species injections. As postulated from observations [Birn et al., 1997a], these categories can be attributed to a dawn-dusk displacement of the ion and electron injection boundaries in combination with an earthward motion or expansion. The simulated electron injection region extends farther toward dusk at lower energies (say, below 40 keV) than at higher energies. This explains the existence of observed energetic ion injections that are accompanied by electron flux increases at the lower energies but not by an energetic electron injection at energies above 50 keV. The simulated distributions show that flux increases are limited in energy, as observed. The reason for this limitation and for the differences between the injection regions at different energies is the localization in the dawn-dusk direction of the tail collapse and the associated cross-tail electric field, in combination with a difference in the relative importance of
Belian Richard D.
Birn Joachim
Borovsky Joseph E.
Hesse Matthias
McComas David John
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