Dependence of magnetic field just inside the magnetopause on subsolar standoff distance: Global MHD results

Abstract

The subsolar magnetopause is the boundary between the solar wind and the Earth’s magnetosphere, where reduced solar wind dynamic pressure is equal to the magnetic pressure of the Earth’s outer magnetosphere. We use a global magnetohydrodynamic (MHD) model to estimate the ratio f of the compressed magnetic field just inside the subsolar magnetopause to the purely dipolar magnetic field. We also compare our numerical results to a similar work by Shue, which used Time History of Events and Macroscale Interactions during Substorms (THEMIS) data. Our results show that the ratio f is linearly proportional to the subsolar magnetopause standoff distance (r0) for both the northward and southward interplanetary magnetic field, properties consistent with Shue but with a smaller proportionality constant. However, previous theoretical studies show that f is nearly independent of the subsolar standoff distance. The global model results also show that f is smaller for the southward Interplanetary Magnetic Field (IMF) under the same r0, and that the proportionality constant for the southward IMF is larger than that for the northward IMF. Both conclusions agree with statistical results from observations by Shue.