Influence of the Interplanetary Magnetic Field Cone Angle on the Geometry of Bow Shocks

Abstract

The frozen-in interplanetary magnetic field (IMF) in the solar wind is one of the most important parameters affecting the Earth’s space weather. In the early studies of the IMF’s influence on space weather, significant effects of the north–south component of the IMF B Z were emphasized, while the radial component of the IMF B X was largely ignored. However, the IMF near the Earth is not always dominated by the north–south component of the IMF B Z , and the radial component of the IMF B X also plays an important role. However, while the effects of the IMF B X (cone angle) on the magnetopause have been studied in recent years, there has been much less effort to quantify the B X (cone angle) effects on the bow shock. In this paper, using the bow shock crossing data from multiple satellites, we investigate the IMF cone angle effect on the dayside and nightside of the bow shock. Our results show that under the radial IMF condition, the dayside of the bow shock is located closer to the Earth than the average. At the same time, on the nightside, the bow shock is farther away from the Earth than the average. The mechanism explaining the bow shock location under the radial IMF is not completely understood. We believe that the magnetosonic Mach number and unusual conditions of the magnetosheath, especially for low dynamic pressure, play an important role. In the future, more work is needed to describe the reactions of the Earth’s magnetosphere to different IMF orientations, especially to the radial IMF.