The polar onset and development of the November 8 and 9, 1991, global red aurora

Abstract

On November 8, 1991, a major magnetic storm began with a sudden commencement at 0647 UT; it continued until about 1800 UT on November 9. Associated with this storm there was a great aurora which continued through November 8 and until at least 1200 UT on November 9. The first optical indication of this event was the appearance of bright sun‐aligned arcs over Eureka, North West Territories (89° corrected geomagnetic latitude (CGM)), Canada from 0750 UT until about 1230 UT on November 8. By that time, there was a gradual transformation to dominant 6300 Å emission over the central polar cap. Gradually, the major soft electron precipitation and associated red aurora moved equatorward. The aurora reached a low‐latitude limit of 40° CGM at 0600 UT on November 9. The polar arcs reached 22 kR intensity (5577 Å), while the red aurora seen later at low latitudes was at least 100 kR (6300 Å). The analysis of Defense Meteorological Satellite Program (DMSP) particle data from 83 passes during November 8 and 9 showed the extent and movement of precipitation from the polar region to midlatitudes. A comparison of this event was made with the earlier great auroral event of March 13–14, 1989. While the extent in low latitude and the duration of the two disturbances were similar, the November 8–9 event had approximately one half of the total energy input into the ionosphere. Its striking and unusual feature was the auroral onset and activity in the central polar region, a feature possibly related to the solar wind interplanetary magnetic field orientation.