Summary
From 1997 to 1999 a series of campaigns were undertaken at the Australian Antarctic polar cap station Casey (-80.6o CGM latitude) with the aim of identifying and gaining further understanding of polar patches. The main instrument used for these campaigns was a Lowell Digital Ionosonde (DPS-4), running a 3 minute cycle of ionograms and drift velocity measurements. Polar Patches were identified from group range and critical frequencies on the ionogram records or from optical measurements at 630 nm with a wide-angle-photometer. These were compared with drift velocity measurements and other geophysical data sets. Good correlations were observed with Total Electron Content derived from GPS satellite observations with a receiver also located at Casey. The influence of the Interplanetary Magnetic Field on the formation and occurrence of patches was also investigated. Comparison with plasma drift velocities, (derived from DPS drift measurements), indicated that patches are associated with fluctuations in the magnitude and direction of horizontal drift velocity. In the current study, peaks in the horizontal velocity magnitude tend to correlate with the patch edges. Further investigations of polar patches have involved comparison with other Digisondes (Zhong Shan), GPS scintillation measurements, riometer absorption readings and SuperDARN radar observations (Syowa).