Numerical simulation of electron distributions upstream and downstream of high Mach number quasi-perpendicular collisionless shocks

Abstract

Test particle calculations are performed to investigate the effects of different shock parameters on electron distributions upstream and downstream of quasi-perpendicular model shocks. The electron trajectories are followed exactly, and the model shock profiles are carefully prescribed as typical internal structures relevant to Earth's bow shock. Kuncic et al.'s [2002] model is employed to calculate the net cross-shock potential jump. A detailed argument for neglecting the noncoplanar magnetic field component is given. The results show that the primary effects on the upstream and downstream electron distributions are determined by (1) variation of the angle θbn between the upstream magnetic field and shock normal, (2) the existence or not of overshoots in magnetic field and cross-shock potential, (3) the spatial profile of the cross-shock potential relative to the magnetic field, and (4) the spatial scale of the shock. Changes in the scale and amplification factors of the shock foot (providing the foot remains small compared with the overall shock), and in the spatial scale of a non-self-consistent Gaussian model for the cross-shock potential, have little effect. The electron distributions, both upstream and downstream, agree very well with the predictions of adiabatic theory. Realistic shocks with self-consistent magnetic and potential profiles have well-defined loss cones, ring beam, and beam features in the upstream and downstream distributions. Leakage of downstream electrons into the upstream region significantly affects the upstream distributions and should not be neglected. Remote extraction of shock structure and parameters appears possible using upstream or downstream electron distributions. Calculations of the wave growth, and resulting particle heating and acceleration, from these distributions should be pursued for time-stationary or reforming shocks with realistic shock profiles. Copyright 2008 by the American Geophysical Union.