RADAR OBSERVATIONS OF MAGNETOSPHERE-IONOSPHERE COUPLING AT MID AND HIGH-LATITUDES

Radar observations from Millstone Kill have identified many interestin g phenomena associated with magnetosphere-ionosphere coupling processe s at the equatorward edge of the auroral region. A number of important magnetospheric boundaries are found near the latitude of the radar fa cility (55 degrees magnetic) and these result in the structure and dyn amics which characterize the pre-midnight sub-auroral ionosphere. The equatorward extent of the plasma sheet particle population lies on fie ld lines near the plasmapause and precipitation from the plasma sheet alters the ionospheric conductances, currents and fields. During distu rbed conditions, an intense (>100 mV/m) polarization electric field ca n be set up when freshly-injected plasma sheet ions lie equatorward of the electrons and this drives the latitudinally-narrow polarization j et or Sub-Auroral Ion Drifts (SAID) which directly or indirectly resul t in a variety of ionospheric phenomena in the pre-midnight sector. As sociated with the region of strongest convection, a deep, narrow F reg ion trough forms while, equatorward of this, sunward advection of plas ma from later local times and lower latitudes leads to the region of S torm-Enhanced Density (SED). The pre-midnight polarization jet produce s strong frictional heating near the F peak resulting in an expansion of the topside and heavy ion outflow which populates the magnetosphere with ionospheric O+. Stable Auroral Red arcs (SAR arcs) occur within the narrow trough, coincident with the polarization jet electric field s and the elevated electron temperatures found there.