Interplanetary control of high latitude electrodynamics.

Abstract

This paper reviews recent observational developments concerning the influence of the solar wind (SW) and the interplanetary magnetic (IMF) field on magnetospheric processes. Examples are chosen to demonstrate that the influence of the SW/IMF is global in scope. Subsequent to sudden compressions of the magnetosphere observed by the Dynamics Explorer satellite the entire auroral oval is bombarded by previously trapped particles. Whether this is followed by a main phase storm or a theta aurora depends on the north-south polarity of the IMF. The potential drop across the polar cap is shown to correlate with the interplanetary electric field. However the potential across the polar cap is much less than the potential across the magnetosphere in the solar wind. The influence of the azimuthal component and ionospheric conductivity on the polar cap convection pattern is discussed in terms of recent observations from the Dynamics Explorer satellite. During periods of northward IMF, regions of sunward convection, with an attendant field-aligned current system, are found in the sunlit ionosphere on the day side of the magnetic dawn-dusk meridian. On the night side of this meridian and in the darkened polar cap, electric fields and field-aligned currents show filamentary structures. Electron precipitation in the polar cap varies from nearly uniform polar rain during periods of southward IMF to structured polar rain and sun-aligned arcs when the IMF has a northward component. The theta aurora detected by the imaging system on Dynamics Explorer appears in regions of sunward convection accompanied by downcoming O+ ions. This suggests that the lobes of the magnetotail are bifurcated by closed, plasma sheet field lines. At lower magnetic latitudes the systematics of the equatorward boundary of auroral electron precipitation are indirectly controlled by the interplanetary electric field. For low to moderate levels of Kp, reasonable estimates of the polar cap potential may be derived from the positions of this boundary.