Simultaneous satellite and ground-based observations of polar cap aurora

On August 20, 1979 (15-17 UT) the sun-aligned polar cap arcs have been observed at the Antarctic station Vostok Simultaneously NOAA polar spacecraft detected in the polar cap a several hundred kilometers wide region of electron and proton precipitation over those arcs, and similar precipitation structure was also observed in the northern polar cap. Within this auroral precipitation regions (interpreted as a signature of the Theta-aurora) the >30 keV proton precipitation have been also found with the intensities comparable with those in the auroral zone. These observations suggest that the Theta-aurora precipitation has its origin on the closed field lines of the plasma sheet.