Field-aligned current reversals and fine structure in a dayside auroral arc

A serendipitous event is reported in which the MAGSAT satellite intercepted an auroral arc over Svalbard, Norway where an all-sky television camera, a photographic camera and a meridian scanning photometer were making continuous measurements. The high time resolution of the optical measurements and the high spatial resolution of the magnetometer data are combined to investigate the relationship between the fine structure in the field-aligned current reversals and the temporal and spatial morphology of the auroral structure. Meridian scans of several optical emissions in the auroral arc, which had its upper portion in sunlight, are utilized to derive the total energy input and the intensity of the precipitating energetic electrons. The MAGSAT satellite apparently intercepted a fold within an extended intense upward current sheet. The current carried by the energetic electrons responsible for the optical aurora is found to be smaller than the field-aligned current derived from the magnetic perturbations, implying that there may be a large flux of low energy particles in this arc. Within the spatial-temporal constraints of this event there is a suggestion that the rayed structure is related to the field-aligned current reversals.