Variations in lower thermosphere dynamics at midlatitudes during intense geomagnetic storms

High-resolution observations of the dynamics of the ionospheric E region (100-150 km) at midlatitudes have been made with the incoherent scatter radar at Millstone Hill (42.6°N, 71.5°W) during several intense geomagnetic storms (K_p - 8-9). These included the storms of 25 September 1998, 15 July 2000, and 31 March 2001. The observations reveal electric fields of up to 100 mV/m during these events and indicate E region zonal plasma drifts of 300-1000 m/s, westward in the evening sector and eastward in the morning sector, with smaller meridional drifts. The tidal pattern of neutral winds in the lower thermosphere is heavily disrupted. The zonal component of the neutral wind follows convection-driven ion flow, while the meridional component shows a more complex response to geomagnetic forcing.