Electrostatic potential in the auroral ionosphere derived from Chatanika Radar observations

Abstract

A technique is described for determining the latitudinal variation of the electrostatic potential associated with the ionospheric convection electric field. Using the north‐south electric field component derived from radar convection velocity experiments, the integral of E• dl is taken northward along the magnetic meridian, starting at low latitudes. The radar data consist of up to 40 independent measurements of plasma convection spanning 15° of invariant latitude centered on Chatanika, Alaska (65°Λ), with half‐hour temporal resolution. It has been found that (1) the electric field contributions to the potential at and below 60°Λ are small under most circumstances and (2) the latitudinal variation of the potential is smooth and regular, permiting the potentials to be contoured across local time. It is found from the experiments that the potential often varies uniformly over 10° latitude at dawn and dusk. Electric fields of 50 mV/m are common. It is also noted that the latitude of the greatest negative potential in the premidnight sector coincides with the Harang discontinuity in ionospheric currents. The potentials calculated from the measured plasma drifts exhibit a regular local time variation. Equipotential contours derived from the latitude‐local time potential field obtained with the long‐duration radar experiments, while not providing a snapshot of the instantaneous pattern, elucidate the large‐scale diurnal variation of the electrostatic potential at auroral latitudes. From such contours it is found that a two‐cell convection pattern with varying degrees of asymmetry is consistently present at auroral latitudes, that a cross‐polar cap potential drop of 70–120 kV is present in moderately disturbed conditions, and that substorms perturb the potential pattern at all local times.