What do we really know about auroral acceleration?

Abstract

The auroral acceleration region provides an easily accessible region where plasma acceleration processes of solar and cosmic importance can be studied. In addition the auroral acceleration region plays an important role in the magnetosphere. The acceleration of ions in the auroral acceleration region provides an important, and at least during times of large magnetic storms, the dominant source of mass to the magnetosphere while the acceleration of electrons produce beautiful auroral displays. While many of the effects of auroral acceleration are understood since it is relatively easy to measure energetic particles, the mechanisms by which particles are accelerated are less well known since a study of mechanisms requires a combination of measurements of both particles and electric fields, preferably at more that one point, with a theory that describes the creation of such electric fields and the effect of such fields on particle acceleration. Measurements by sounding rockets and satellites dedicated primarily to auroral studies such as S3-3, DE, and Viking have provided much of the in situ observations that are the basis of our current knowledge of auroral acceleration. Currently, Freja, Akebono, and especially the Polar and FAST satellites, together with increasingly more sophisticated sounding rockets are adding to our knowledge of auroral acceleration.