Incoherent scatter radar observations related to magnetospheric dynamics

Over the past decade incoherent scatter radars have provided fundamental observations of velocities and plasma parameters in the high-latitude ionosphere which relate to the dynamical processes responsible for the excitation of flow in the coupled solar wind-magnetosphere-ionosphere system. These observations have played a central role in inspiring a change of paradigm from a picture of quasi-steady flows parameterised by the direction of the interplanetary magnetic field to a picture of inherently time-dependent flows driven by coupling processes at the magnetopause and in the tail. Flows and particle precipitation in the dayside ionosphere are reasonably well understood in principle in terms of the effects of time-dependent reconnection at the magnetopause, though coordinated high-and low-altitude observations are lacking. Related phenomena also appear to occur in the tail, forming the ''equatorward-drifting arcs'' which are present during quiet times, as well as during the growth and early expansion phases of substorms. At expansion onset, the substorm bulge forms well equatorward of the are formation region, and may take similar to 10 min or more to reach it in its poleward expansion. Nightside ionospheric flows are then considerably perturbed by the effects of strong precipitation-induced conductivity gradients. (C) 1997 COSPAR. Published by Elsevier Science Ltd.