The High Latitude Boundaries Under Extreme Solar Wind Conditions: a Cluster Perspective

Abstract

The high latitude boundaries include boundary between the magnetosheath and cusp, the boundary between the magnetosheath and the High Latitude Trapping Region (HLTR) which is the closed field line region on the day-side in the high latitude region, the boundary between cusp and HLTR and the boundary between mantle and cusp. The properties of the high latitude boundaries vary rather dramatically under different solar wind conditions. We present statistical results based on four years of data obtained by Cluster when these spacecraft were in the vicinity of the dayside magnetopause. During northward Interplanetary Magnetic Field (IMF), the interfaces between the magnetosheath and cusp are rather clear. The changes of the energetic particle flux, plasma temperature, density, and velocity across the magnetopause under northward IMF were analyzed by superposed epoch analysis. The plasma flow and density decrease, and the proton temperature increases across the magnetopause from the magnetosheath into the cusp. Further, during extreme storm times, the cusp is more turbulent than during quiet times and there is no clear plasma density change across the magnetopause. During low density solar wind conditions, the magnitude of the parallel temperature change across the magnetopause is larger than during high density solar wind conditions. And the magnitude of the plasma density and velocity change is smaller than during high density solar wind conditions.