Longitudinal and interhemispheric variations of auroral ionospheric electrodynamics in a realistic geomagnetic field

Abstract

We investigate the influences of nondipolar features of the geomagnetic field (field strength, orientation, and magnetic coordinate distortion) on auroral ionospheric electrodynamics. We present a conceptual model in which both the electric potential and the distribution functions of precipitating auroral particles are invariant in the magnetic latitude/magnetic local time reference frame, and we explore the predictions of this model concerning longitudinal (or universal time) and interhemispheric (north/south) variations of auroral electrodynamic parameters at ±68° magnetic latitude for a fixed magnetic local time and solar zenith angle. The conductances, electric fields and currents, ion drift velocity components, and Joule heating tend to have two minima and maxima with respect to longitude in the northern hemisphere but have a single minimum and maximum in the southern hemisphere. Particularly large variations are found for the field‐aligned current density (maximum/minimum = 1.76) and the regional Joule heating (maximum/minimum = 1.88), with maxima near northwest Iceland and northwest Alaska, and minima over north‐central Siberia and Hudson Bay. The variations of field‐aligned current intensity may imply a tendency for more frequent field‐aligned electron acceleration and thus brighter aurora near northwest Iceland and northwest Alaska than elsewhere. The longitudinal variations of Joule heating may contribute significantly to universal time variations of total hemispheric Joule heating. Whether or not the conceptual model is correct, at least some of the various electrodynamic parameters must have longitudinal and hemispheric variations of the general magnitudes the model predicts.