How important are dispersive Alfvén waves for auroral particle acceleration?

Abstract

The means by which charged particles are accelerated in space to form the aurora is still not fully understood. This acceleration produces earthward streaming electrons driving auroral luminosity and outward streaming ionospheric ions which populate space with terrestrial matter. With the advent of high resolution space borne field and particle instruments, dispersive Alfvén waves (DAWs) have been identified as drivers of auroral particle acceleration and it has been shown that the Alfvén wave energy observed is sufficient to power a significant fraction of auroral luminosity. Since previously it has been considered that auroral particle acceleration occurs in quasi‐steady field‐aligned currents, quantifying the amount of particle acceleration occurring in DAWs relative to the traditionally invoked processes is fundamental to our understanding of how the aurora works. We combine coincident satellite measurements of fields and particles to demonstrate that as functions of increasing auroral activity 25–39% of the total electron energy deposited in the ionosphere and 15–34% of total energetic ion outflow may be attributed to the action of DAWs. In fact in the vicinity of the polar cusps and pre‐midnight auroral oval, DAWs may provide the dominant means for powering electron and ion acceleration during active times.