Imaging and in Situ Particle Observations of Particles Accelerated by Auroral Electric Fields

Images from the IMAGE Wide-band Imaging Camera (WIC) and Spectrographic Imager (SI) channels SI12 and SI13, were compared to in situ data taken by FAST for several cases of substorm onsets and following auroral conditions. FAST spacecraft observations had shown that the high latitude auroral ionosphere has several distinct regions and two of those are associated with intense particle precipitation The upward current region contains converging electric field structures, large-scale density cavities, down-going inverted V electrons and quasi-static potential structures. Another, sometimes distinct, region is characterized by filamentary currents containing Alfvenic electric fields, field aligned counter streaming (superthermal) electrons and ion heating transverse to B with associated large ion outflow. In two of the cases presented the satellite passed through the substorm surge on its duskward flank fairly soon after substorm onset. In these cases the superthermal wave accelerated component was clearly found to be on the polar cap boundary of the surge and could be isolated from inverted V precipitation which occurred in the more equatorward parts of the auroral oval. It is suggested that the wave accelerated precipitation is the signature of intense earthward-directed, Alfvenic Poynting fluxes usually observed at altitudes of 4-6 Re near the lobe/plasma sheet interface. In one of the cases the surge was accompanied by intense ion outflow. In three of the cases presented FAST passed through the substorm aurora at midnight or the dawn side outside of the surge and the wave accelerated electrons were less clearly separated from the inverted V type precipitation and the wave accelerated, electrons were seen to be part of very short lived transient events i.e. bursts. The ions were present equatorward of the surge with no enhancement poleward of their normal auroral oval position. The region of auroral forms, associated with intense Alfven waves propagating from the magnetosphere, are most likely to be produced by rapidly moving field lines through (substorm) dynamic reconfiguration unlike inverted V type electric field structures which may be produced by steady plasma convection. The ability to image the two different types of auroras would allow to map the field lines connected to regions of dynamic field configuration.