Interplanetary magnetic field control of fast azimuthal flows in the nightside high-latitude ionosphere

SuperDARN radar data from both hemispheres for the interval January 1999 to November 2006 have been inspected for evidence of high-speed azimuthal flows in the nightside high-latitude ionosphere. In the northern hemisphere, 88% of the westward directed fast flows occurred during IMF BY negative intervals and 83% of the eastward flows occurred during IMF BY positive intervals. In the southern hemisphere 82% of the westward flows occurred during IMF BY positive intervals and 74% of the eastward flows occurred during IMF BY negative intervals. ∼74% of these fast flows occurred when the IMF was within the 30° < ∣ ∣ < 100° clock angle range and the AE index was below 150 nT. These results support the hypothesis that highly dynamic magnetospheric activitycan be associated with predominantly northward, but BY-dominated IMF driving conditions and subsequent non-substorm reconnection in a twisted magnetotail.