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We investigate theseasonal, local solar time, and geomagnetic activity variations of the averageDoppler velocity measured by an HF digital ionosonde deployed at Bundoora,Australia (145.1° E, 37.7° S, geographic; 49° S magnetic). The Dopplervelocities were heavily averaged to suppress the short-term effects (<3hours) of atmospheric gravity waves, and thereby obtain the diurnal variationsattributed to the tidally-driven ionospheric dynamo and electric fieldsgenerated by magnetic disturbances. The observed seasonal variations in Dopplervelocity were probably controlled by variations in the lower thermospheric windsand ionospheric conductivity above Bundoora and in the magnetically conjugatelocation. The diurnal variations of the meridional (field-perpendicular) driftsand their perturbations exhibited a complex structure, and were generallysmaller than the variations in the zonal drifts. The latter were basicallystrongly west-ward during the evening to early morning, and weakly east-wardduring the late morning to just past noon. The zonal perturbations were stronglyenhanced by increasing geomagnetic activity, and closely resembled theperturbation drifts measured by the incoherent scatter radar (ISR) at MillstoneHill (71.5° W, 42.6° N; 57° N). There was also some resemblance between thediurnal variations in the meridional drifts. Overall, the comparisons suggestthat with sufficient averaging, Doppler velocities measured with digitalionosondes at mid-latitudes correspond to true ion motions driven by ionosphericelectric fields. This is a useful result because apart from the ISRs located inthe American-European sector, there are no ground-based instruments capable ofmeasuring electric fields in the mid-latitude ionosphere.  <b>Key words. </b>Ionosphere (electricfields and currents; ionosphere atmosphere interactions; mid-latitudeionosphere

Seasonal and magnetic activity variations of ionospheric electric fields above the southern mid-latitude station, Bundoora, Australia