THE INFLUENCE OF GEOMAGNETIC-ACTIVITY ON THE UPPER MESOSPHERE LOWER THERMOSPHERE IN THE AURORAL-ZONE .2. HORIZONTAL WINDS

A spaced antenna partial reflection radar located at Mawson, Antarctica (67 S, 63 E, invariant latitude 70 S), has been used to measure the horizontal wind field in the height range 70-110 km. Three years of data (1985-1987) from the radar have been analysed in order to investigate correlations between geomagnetic activity (determined from the local K-index) and the horizontal wind. Results are analysed using a randomization technique and show that larger winds are measured during geomagnetically active periods in both the raw (or unfiltered) wind values and in the medium-frequency (2-6 h period) and high-frequency (1-3 h period) components. The raw winds tend to be shifted towards the geographic NW to NE quadrant in the early morning hours during high K-times. The observed correlation is seen down to 86 km and shows a seasonal dependence. The mean r.m.s. velocity of the radar scatterers and the angular spread of the return echoes are also found to be correlated with geomagnetic activity. The medium- and high-frequency components of the wind are polarized in the magnetic zonal direction during all seasons of the year.