Interplanetary Magnetic Field By Controls the Magnetopause Location

Abstract We present a statistical study of interplanetary magnetic field (IMF) effects on the magnetopause location based on nearly 15,000 magnetopause crossings identified in the THEMIS A‐E, Magion 4, Geotail, and Interball‐1 satellite data. In order to exclude the dominant controlling role of the solar wind dynamic pressure, differences between observed and empirical model magnetopause distances are analyzed. We find that the magnetopause distance is significantly controlled by the IMF clock angle, not considered in the used empirical models. Furthermore, during very low Alfvén Mach numbers (MA < 4), IMF By component can induce a considerable dawn‐dusk asymmetry of the magnetopause shape. The magnetopause distance is found to be larger in the direction of the IMF vector, that is, not only the magnitude but also the orientation of the IMF By component is eventually important. The obtained results are qualitatively consistent with a magnetohydrodynamic model run at the Community Coordinated Modeling Center.