THE THICKNESS AND STRUCTURE OF HIGH BETA-MAGNETOPAUSE CURRENT LAYER

Previous surveys of the magnetopause current layer indicated that its thickness ranges from 200 to 1800 km and on average is about 900 km or approximately 10 ion gyroradii [Elphic and Russell, 1979; Berchem and Russell, 1982]. In the present study, we have used ISEE magnetic field data to examine the magnetopause current layer under high beta magnetosheath conditions. Under high beta conditions, we find that the current layer is thinner than observed under typical conditions. The thickness is typically between 200 to 600 km and the peak of the distribution scales to 2-4 ion gyroradii for the high beta magnetopause. However, the velocity of the magnetopause is found to be highly variable similar to the highly variable distribution observed under more typical conditions. A wave-like structure is often observed at the foot of the current layer extending from the current layer into the magnetosheath. The presence of this propagating wave structure at the foot of the magnetopause may lead to some confusion in attempts to determine the thickness of the current layer with a single spacecraft.