Observations of the radial magnetosheath profile and a comparison with gasdynamic model predictions

Abstract

The gasdynamic model of the magnetosheath flow predicts changes of plasma parameters across the magnetosheath. According to this model, the ion flux peaks at the bow shock and decreases toward the magnetopause. MHD models predict a further plasma depletion near the magnetopause for specific orientations of the interplanetary magnetic field. We present a statistical study of ion flux measurements on the dusk flank of the magnetosheath and its comparison with present magnetosheath models. The study is based on three years of INTERBALL‐1 measurements supported by simultaneous WIND solar wind observations. Our results reveal a much flatter magnetosheath radial profile than was expected from the gasdynamic prediction. The profile becomes steeper for higher upstream Mach number or plasma beta. The depletions of the ion flux behind the bow shock and at the magnetopause are attributed to the reflection and acceleration of particles in the bow shock region and magnetopause reconnection, respectively. A comparison of the measured and predicted ion fluxes suggests that the magnetosheath thickness is a rising function of the IMF magnitude.