October 1998 WLS Experiment

Rotation of Convection Pattern during IMF By Flip

The Millstone Hill Radar was performing a sequence of azimuth and elevation scans to monitor ionospheric characteristics and convection over a wide span of latitude and local time. This mode gave ~35 min temporal resolution between repeat coverage of the same area. Elevation scans to the North indicated increasing poleward velocity at high latitudes during the interval preceeding the By sector change. Observations of the change in velocity at two latitudes indicate that only the portion of the convection pattern poleward of 66 def Invariant rotated during the event.

The Millstone Hill operating mode was changed to hold a fixed antenna pointing position to the NE (12 deg AZ) and to sample the ExB Doppler velocity (LOS component) with 20 sec temporal resolution in order to observe the change in the dayside convection pattern associated with the anticipated arrival of the IMF sector boundary at Earth. LOS velocity and topside F-region density showed a ppronounced change associated with the sector reversal. Unfortunately, a radar system outage (blown T/R switch) created a 20-min data gap across the actual time of the reversal of the ionospheric patterns. The elevated density observed at the greated ranges (higher latitudes) prior to the reversal is associated with advected solar-enhanced plasma from lower latitudes and later local times (SED).

Integration over 10 consecutive radar data integration periods for the intervals before and after the By sector change show the pronounced change in convection direction and density structure at the higher latitudes.