The IMF dependence of the magnetopause from global MHD simulations

Abstract

Numerical results from a physics‐based global magnetohydrodynamic (MHD) model are used to investigate the controlling effects of the interplanetary magnetic field (IMF) components, BY and BZ, on the location and shape of the magnetopause. The subsolar magnetopause is identified by using the plasma density and velocity, the cusp by using the current density, and the other area by streamlines and the current density. These data are fitted with a three‐dimensional surface function constructed by Liu et al. (2012), which allows description of the cusp geometry as well as the north‐south asymmetry and azimuthal asymmetry of the magnetopause. A new parameter which depends on the IMF BY and BZ is introduced to describe the orientation of the elliptical cross section of the magnetopause. Effects of IMF BY and BZ on the magnetopause configuration parameters are analyzed, and dependence of the magnetopause parameters in the IMF components are obtained. Magnetopause cross section is found to be largely controlled by the IMF clock angle. The stretch direction of the magnetopause cross section is always near the direction of the IMF but is a little closer to the meridional plane than the IMF. Increasing BY or BZincreases the eccentricity of the magnetopause cross section. This effect is larger for southward IMF than for the northward IMF, and the stretching effect of BY is smaller than that of BZ.