Radar studies of midlatitude ionospheric plasma drifts

We use incoherent scatter radar measurements from Millstone Hill and Saint Santin to study the midlatitude F region electrodynamic plasma drifts durin g geomagnetically quiet and active periods. We present initially a local ti me, season, and solar flux dependent analytical model of the: quiet time zo nal and meridional ExB drifts over these stations. We discuss, for the firs t time, the Saint Santin drift patterns during solar maximum. We have used these quiet time models to extract the geomagnetic perturbation drifts whic h were modeled as a function of the time history of the auroral electrojet indices. Our results illustrate the evolution of the disturbance drifts dri ven by the combined effects of prompt penetration and longer lasting pertur bation electric fields. The meridional electrodynamic disturbance drifts ha ve largest amplitudes in the midnight-noon sector. The zonal drifts are pre dominantly westward, with largest amplitudes in the dusk-midnight sector an d, following a decrease in the high-latitude convection, they decay more sl owly than the meridional drifts. The prompt penetration and steady state zo nal disturbance drifts derived from radar measurements are in good agreemen t with results obtained from both the ion drift meter data on board title D ynamics Explorer 2 (DE 2) satellite and from the nice Convection Model.