NNSS satellite observations of medium-scale traveling ionospheric disturbances at southern high-latitudes.

From March 1985 to January 1986, 428 medium-scale traveling Ionospheric disturbances (TID's) incident to the high-latitudes between 50° and 85°S were detected at Syowa Station, Antarctica, by means of differential-Doppler measurements of the 150 and 400 MHz beacon waves from six NNSS satellites. It is found from statistical analysis that (1) the medium-scale TID's at high-latitudes appear quite often during geomagnetically quiet and moderately disturbed conditions, and their occurrence seems not to increase with increasing geomagnetic activity, (2) they attain the maximum activity in winter and the minimum in summer, (3) diurnal variation shows the maximum occurrence around 1400-1600 LT with a second maximum around midnight, and (4) most of the medium-scale TID's propagate from south toward the equator. These findings are compared with TID observations using NNSS made at mid-latitudes (30°-55°N) to find a fairly good consistency between both results.