Summary
During 1997 and early 1998 a series of campaigns were undertaken at the Australian Antarctic polar cap station Casey (-80.8o geomagnetic latitude) with the aim of identifying and gaining further understanding of polar patches. The main instrument used for these campaigns was a University of Massachusetts Lowell, Centre for Atmospheric Research (UMLCAR) Digital Ionosonde (DPS-4), running a three-minute cycle of Doppler ionograms and drift velocity measurements. Patches identified from group range and critical frequencies on the ionogram records were compared with drift measurements and other geophysical data sets. Good correlations were observed with Total Electron Content (TEC) derived from Global Positioning System (GPS) satellite observations with a receiver also located at Casey. The field-of-view for GPS observations allowed patches to be observed over large distances, providing some insight into their origin. The influence of the Interplanetary Magnetic Field (IMF) on the formation and occurrence of patches was also considered. Comparison with plasma drift velocities, (derived from DPS drift measurements), confirmed that patches are associated with fluctuations in horizontal drift velocity. In the current study, peaks in the magnitude of the horizontal drift velocity correlate with the patch edges. This paper considers case studies of three days of patch observations in April 1998.