The role of advection and advective nonlinearities in the creation of quasi-stationary discrete auroral arcs

Discrete auroral arcs are the result of quasi-static magnetic-field-aligned acceleration of electrons to energies of up to tens of keV.  They can remain quasi-stationary for tens of minutes, which places a strong constraint on candidate theories. For example, kinetic or inertial Alfven waves can accelerate electrons along B, but only to energies of the order of 1 keV, and then only in short-lived bursts, which excludes them as an explanation for most discrete arcs.  One type of theory assumes plasma convection across a stationary arc, which introduces time-dependent effects in the frame of the drifting plasma, including polarization current associated with the advective part of the convective derivative of E.  The ion polarization drift velocity can be shown to be of the same order as as the ExB drift across the arc, requiring a fully nonlinear treatment.  This talk will show that this mechanism can lead to field-aligned currents having properties consistent with some observations.