LOW LATITUDE ELECTRODYNAMIC PLASMA DRIFTS - A REVIEW

Radar and radio measurements have provided detailed information on the dependence of F-region electrodynamic drifts on height, season, solar cycle and magnetic activity. Recently, satellite ion drift and electric field probes have determined the variation of low latitude ionospheric drifts over a large range of altitudes and latitudes. The general characteristics of the quiet time plasma can be explained as resulting from E- and F-region dynamo and interhemispheric coupling processes. The low latitude and equatorial zonal and upward poleward components of the plasma drift respond differently to geomagnetic activity. Disturbance dynamo effects are responsible for the drift perturbations following periods of enhanced magnetic activity. The prompt penetration of high latitude electric fields to lower latitudes produces large perturbations on the upward poleward drifts, but has no significant effect on the low latitude and equatorial zonal drifts. A number of processes such as 'overshielding', 'fossil wind' and magnetic reconfiguration were suggested as being responsible for the direct penetration of high latitude electric fields to lower latitudes. Detailed low latitude and global numerical models were used to study the characteristics of low latitude and equatorial plasma drifts and their response to changes in the polar cap potential drop or in the high latitude field-aligned currents. These models can reproduce the latitudinal variation of the perturbation electric fields and their diurnal variations, but are still unable to account for several aspects of the experimental data as a result of the complexity of the high latitude and magnetospheric processes involved.