Mithras Studies of the Boundary between Open and Closed Field Lines

摘要

The coupling between the solar wind, the magnetosphere, and the ionosphere wasstudied using data from multi-instrument campaigns. One study showed that, even under quiescent conditions, the polar cap boundary was quite active. Repeated disturbances in particle precipitation and electric field were observed at intervals of 10 to 20 minutes. Some of these perturbations propagated westward at a velocity of around 1000 m/s. It was argued that these perturbations are the ionospheric signature of rapid increases in the midnight-sector magnetic reconnection. In a separate study, the transition from active to quiet conditions was examined. The interplanetary magnetic field northward component switched suddenly from a northward to a southward orientation. The ionosphere responded within about two minutes: the electric field intensity diminished, and the F-region large and small scale irregularities changed dramatically. This response time is much shorter than had previously been assumed.