Distribution of auroral precipitation at midnight during a magnetic storm

On the night of November 4, 1986 a very complex precipitation pattern was observed by the Swedish satellite Viking in the magnetic midnight sector over Scandinavia and Svalbard. The pass took place during a magnetic storm, but during substorm recovery phase. Going from north to south the satellite first encountered a plasma region of bps-type and then a region of cps-type. Then, however, a new region of bps-type was traversed. The quite intense most equatorward aurora corresponded to a plasma region which was not of ordinary cps-type but contained sharp quasimonoenergetic peaks. The high latitude midnight sector was totally dominated by eastward convection. The Harang discontinuity had passed northern Scandinavia the first time as early as between 18 and 20 MLT, more than three hours before the Viking pass. It is suggested that the particle precipitation pattern and the general shape of the aurora as observed by the Viking imager can be explained in a natural way by the convection pattern. The northernmost bps- and cps-type regions originated in the morning side convection cell while the more equatorward population of bps-type had drifted in from the evening side.