Statistics on the Magnetosheath Properties Related to Magnetopause Magnetic Reconnection

Abstract Magnetosheath properties, particularly those related to magnetopause magnetic reconnection (MR), are investigated in this study. (1) Asymmetries are found to exist in the distributions of plasma and magnetic field parameters in the magnetosheath. These asymmetries are related to the interplanetary magnetic field (IMF) orientation, and they are produced either on the bow shock or inside the magnetosheath. Thus, one must be very cautious in directly using the upstream solar wind and IMF properties as the magnetopause MR initiation conditions, since the magnetosheath parameters are not the same everywhere. (2) A unique method is introduced to estimate how much IMF magnetic flux passes through the magnetosphere via MR on either the low-latitude or the high-latitude magnetopause. This flux mainly varies with three independent parameters: the IMF clock angle θ CL, the magnetosheath plasma β, and the solar wind sound Mach number M S . Surprisingly, the magnetic fluxes passing through the magnetosphere are comparable under the southward and northward IMF conditions. (3) The dipole tilt angle, the property from the inside of the magnetosphere, also controls the magnetosheath parameters. As the Earth’s dipole tilt angle varies, the plasma pressure ridge shifts its location but remains near the magnetic equator. The stagnation point of the magnetosheath flow on the magnetopause, however, remains at the subsolar point no matter how large the dipole tilt angle is. These behaviors may be determinative of the locations of MR and the generation of flux transfer events on the magnetopause.