The role of enhanced thermal pressure in the earthward motion of the Earth's magnetopause

The magnetopause is the thin boundary between the solar wind and the Earth's magnetic field. The magnetopause moves earthward as the total pressure just inside the magnetopause is reduced or the total pressure just outside the magnetopause is enhanced. It has been suggested for more than four decades that field-aligned currents, created by magnetic reconnection for southward interplanetary magnetic field, reduce the magnetic pressure just inside the magnetopause. Under the assumption of a constant total pressure just outside the magnetopause, the magnetopause consequently moves earthward. Here we show that the reduced magnetic pressure just inside the magnetopause is insufficient to account for its earthward motion to its real location. For this to happen, an enhancement in the total pressure just outside the magnetopause is required. Our observations also reveal that the enhanced thermal pressure is the major contributor to the total pressure enhancement. Key Points Total pressure just outside the magnetopause is enhanced for southward IMF. Enhanced thermal pressure is the main contributor to total pressure enhancement. A larger dynamic pressure contributes more thermal pressure on the magnetopause.