Superrotation of the ionosphere and quiet time zonal ion drifts at low and middle latitudes observed by Republic of China Satellite-1 (ROCSAT-1)

Abstract

Local-time variations of zonal drifts at different latitudes, longitudes, and seasons are investigated using ion drift measurements from the Republic of China Satellite-1 (ROCSAT-1). We select a quiet time period defined when Dst >-100 nT and Kp ≤3. The ion drifts in the magnetic zonal direction are latitude (apex height) dependent and differ for different longitude sectors and seasons. Superrotation of the ionosphere is observed in the zonal drift measurements, particularly at the lower latitudes. The ionospheric superrotation generally decreases with increasing latitude and is attributed mainly to the F region dynamo where the features of the neutral wind and conductance affect the characteristics of the superrotation at different latitudes, longitudes, and seasons. We suggest that the latitudinal variation of the superrotation is mainly produced by the decrease in latitude of the neutral winds in the F region. A decrease of conductance with increasing latitude is also present, but evidence shows that neutral winds decrease faster with latitude than the conductance for high solar flux conditions. The longitudinal and seasonal variations of the superrotation are more influenced by changes in the F region conductance that is modified by vertical E × B ion drift motions and neutral wind-induced ion drift motions along magnetic field lines. © 2011 by the American Geophysical Union.