Observed response of the Earth's lower thermosphere to a major geomagnetic storm

Abstract

In response to a geomagnetic storm alert in early June 1991, the incoherent scatter radar at Millstone Hill and the meteor wind radar at nearby Durham, both located at 43°N, 71°W, were activated to observe the effects of the storm on the earth's mesosphere and lower thermosphere. The storm is characterized by Kp indices of 6–8 during the first three days of observations which spanned June 11–14. Winds as large as 120–150 m/s in the zonal component and 100 m/s in the meridional component were measured at 109–115 km altitude, and the maximum zonal wind component on the most disturbed day was roughly twice as large as that observed during relatively more quiet geomagnetic conditions in June 1989. The semidiurnal tidal structure that generally characterizes this region of the upper atmosphere appears to be preserved while the amplitudes are greatly enhanced. The observed winds in the mesophere do not reveal a reaction to the geomagnetic storm, and when combined with the incoherent scatter radar data, show excellent continuity with altitude. The large winds observed at 105–120 km contrast with predictions from general circulation models of the thermosphere.