Summary
A Lowell Digital Ionosonde (DPS-4) has been used at the Australian Antarctic polar cap station Casey (-80.6° CGM latitude) in a study of ionospheric polar cap patches. The instrument ran a series of campaigns consisting of 3 minute cycles of ionograms and drift velocity measurements during 1997-1999. Patches were identified from group range and critical frequencies from ionograms and then compared with drift measurements and other geophysical data sets. Comparisons with plasma drift velocities, (derived from DPS drift measurements), indicate that patches are often associated with fluctuations in horizontal drift velocity. This paper will present the latest results on this project, and discuss the possible causes of the velocity fluctuations.