FIELD-ALIGNED CURRENTS ASSOCIATED WITH SPATIALLY PERIODIC X-RAY STRUCTURES IN THE MORNINGSIDE AURORAL OVAL

On February 9, 1992, the Atmospheric X ray Imaging Spectrometer (AXIS) on the Upper Atmosphere Research Satellite (UARS) observed spatially periodic structures in X ray luminosity from the top of the atmosphere during a pass over the dawnside auroral oval. The patches of luminosi ty were several hundred kilometers in size and separated by a mean dis tance of about 700 km. As many as a dozen distinct patches could be id entified extending from local times just after midnight to the noon me ridian. The characteristics of the precipitating electrons responsible for the patches were determined from the measured X ray fluxes. Peak electron energy fluxes were between 4 and 10 ergs cm(-2) s(-1) with c- folding energies of 10-25 keV, In situ magnetic field data from the on board magnetometer were used to model the field-aligned currents assoc iated with two of the patches. The model that best fit the data had up ward currents in the western portions of the patches and more intense downward currents confined to the eastern edges. The modeling also ind icated that these small-scale currents were embedded within the large- scale region 2 field-aligned current sheet. Data from a ground-based m agnetometer near the satellite ground track indicated the presence of Ps 6 pulsations. We have interpreted the observations in terms of east ward-drifting current patch systems. Under this assumption, the patche s moved at 1.7 km s(-1), the drift speed of similar to 30-keV electron s. This motion, and the correlation with Ps 6 pulsations suggests that the X lay patches were associated with omega bands that are seen in t he morning sector during geomagnetically active times.