Ion temperature anisotropy in the auroral F-region as measured with EISCAT

Abstract

Measurements by the EISCAT UHF system revealing substantial non-isotropic ion temperatures in the auroral F-region are presented. We find that during such periods, which are connected with strong convection electric field events, the ion energy equation is not sufficient to describe the ion temperature anisotropy observed in this experiment. The ion temperature perpendicular to the magnetic field is found to be larger than the parallel one, and yet also larger than can be expected from the conventional energy balance arguments in the F-region. The increase in the ion temperature parallel to the magnetic field has a close resemblance to the variations in the ion velocity and is therefore associated with Joule heating events. In order to provide energy balance in the direction perpendicular to the magnetic field, additional sources than the conventional ones for ion heating would be required.