Factors controlling the diamagnetic pressure in the polar cusp

Abstract

The solar wind has direct access to the polar cusps although the plasma may be processed first by reconnection. The energy density of the polar cusp plasma is expected to be controlled by the component of the unshocked solar wind dynamic pressure along the normal to the cusp/magnetosheath interface. The factors controlling this angle are the local time of the observation and the dipole tilt angle. We use Polar observations of the magnetic field and plasma to identify the polar cusp, and the change in magnetic pressure in the cusp to calculate the peak diamagnetic pressure of the plasma. As expected this pressure is directly proportional to the solar wind dynamic pressure in quantitative agreement with expectations. When the dipole tilts more toward the Sun, the angle between the solar wind flow and the magnetopause normal is smaller, and the pressure is higher, and when it tilts away from the Sun, the pressure is less. For large tilts away from the Sun, for local times far away from noon and for low solar wind dynamic pressure the diamagnetic depression marking the polar cusp is too weak to be resolved by the magnetometer.