Auroral zone conductivities within the field‐aligned current sheets

Abstract

We have used field‐aligned current data obtained by the Triad satellite during 21 passes over Alaska to order conductivity measurements made simultaneously by the Chatanika radar. Three distinct field‐aligned current regions were sampled during these experiments: the region 2 current sheet in the morning and evening sectors and the region 1 current sheet in the evening sector. The conductances in the region 2 evening sector current sheet increase uniformly with latitude, and the total increase in conductance across the sheet is fairly constant. The latitudinal profiles of conductance across the region 1 evening sector current sheet show that auroral arcs tend to occur in the poleward portion of the sheet. In the morning sector region 2 current sheet the Hall conductance is larger and changes much more rapidly with latitude than the Pedersen conductance. The Hall and Pedersen conductance can be interpreted in terms of the number density and temperature of a Maxwellian distribution of electrons that would produce the same conductance values. We call this electron population the equivalent Maxwellian source. The temperatures and densities thus deduced are similar to those of the electrons in the plasma sheet. Conductances in the region 2 evening sector current sheet indicate a source with a temperature between 0.5 and 2 keV and density between 0.1 and 1 cm−3. The morning sector diffuse aurora within the region 2 current sheet originates from a population with temperatures between 1 and 4 keV and density between 0.6 and 2 cm−3. In auroral arcs the conductances are consistent with those expected from plasma sheet electrons that have been accelerated along magnetic field lines. The concept of equivalent Maxwellian source is also used to study the extent to which the precipitating electrons can carry the field‐aligned current in the various regions.