Magnetosheath and Magnetopause Under Low Mach Number Conditions

We examine plasma and electromagnetic field properties in the magnetosheath and at the magnetopause under low Mach number conditions. We use solar wind conditions as well as empirical magnetopause and shock position estimates in the OMNI database to examine weakening of the shock as the Mach number gets smaller. Magnetosheath conditions are examined using Themis observations, converted to the MIPM coordinate system that organizes data according to quasi-parallel and quasi-perpendicular shock orientation and distance relative to the magnetopause and the shock. The GUMICS-4 global MHD simulations under different Mach number conditions as well as observed time series of individual magnetopause crossings are used to support and complement the statistical analyses. These results are put into context using our earlier study of a nonlinear response of the energy entering the magnetosphere to the energy incident upstream of the shock, and of the saturation of the polar cap potential under low Mach number conditions.