Prediction of Alfvenic turbulence near the magnetospheric sash

Results of global MHD simulations are used to examine the susceptibility of magnetosheath plasma to anisotropy-driven instabilities, specifically the mirror mode, electromagnetic ion cyclotron (EMIC), and firehose instabilities. Advection of magnetosheath plasma is followed along MHD-specified streamlines assuming double-adiabatic equations of state, while the anisotropic pressure is constrained by the instability threshold criteria and the condition that the trace of the gyrotropic pressure tensor be three times the MHD specification for the (isotropic) pressure. Following this procedure, mirror mode and EMIC turbulence is indicated in the dayside magnetosheath and in a layer adjacent to the dayside magnetopause, generally in accord with theoretical and observational expectations. The new result is the prediction of strong firehose or Alfvenic turbulence in the magnetosheath adjacent to the magnetospheric sash. Alfven waves will propagate downwind from the sash. Also, as magnetic field strength increases downwind from the sash, mirror mode and EMIC waves are again indicated. (C) 2002 Elsevier Science Ltd. All rights reserved.