Temporal Stability of Field-Aligned Currents and Electric Fields in the Auroral Oval

Abstract:

The Cluster magnetic field data from several years’ worth of aurora oval crossing is used to quantify the temporal variations of magnetic field signatures of field-aligned currents (FAC). The method is used to study the cross-correlation between pairs of spacecraft as a function of the temporal separation of the auroral crossings of the respective spacecraft. When the method is applied on the large-scale variations associated with the whole auroral pass, it gives results consistent with those of an earlier smaller study using low-altitude measurements of particle fluxes. We then apply the method to study the temporal stability of FAC as a function of latitude, local time, geomagnetic parameters, and the scale sizes of the magnetic field variations. This is contrasted to the temporal stability of electric fields, studied by the same methodology. The FACs and electric fields show similarities in the dependence of temporal stability on location and other parameters, but the stability of the electric fields is consistently smaller than that of the FACs. We discuss some conclusions of this study, in particular as it applies to the nature of auroral acceleration structures.