The polar cusp ionosphere: a window on solar wind–magnetosphere coupling

Abstract

The polar cusp ionosphere is an important part of near-Earth space which is best monitored by ground-based observations made in the remote polar regions. Antarctica seems certain to play a key role in its future exploration. The region is characterized by the direct entry of solar wind particles along magnetic field lines projecting to the dayside magnetopause (outer boundary of the magnetosphere). Thus the polar cusp ionosphere provides a splendid window for examining processes transferring solar wind mass and momentum to the magnetosphere. The review will emphasize this aspect of polar cusp ionosphere research, an area where the pace of recent work has been rapid. New results highlight the relevance of both the interplanetary magnetic field direction and changes in solar wind pressure for dynamic effects in the polar cusp ionosphere. These phenomena include surges in plasma flow, auroral activity, magnetic impulses and field-aligned (Birkeland) currents. Among the theoretical advances emerging just this past year are ones for the origin of plasma transport in the dayside polar ionosphere and for the source of the dayside Region 1 and cusp Birkeland currents.