SOURCES AND VELOCITIES OF PC1-2 ULF WAVES AT HIGH-LATITUDES

The polar cusp and boundary layer are important in coupling magnetosph eric energy sources to the high latitude ionosphere. ULF waves are one of the processes by which this coupling is realized. To study the sou rce regions and propagation characteristics of discrete Pcl-2 (0.1-2 H z) ULF wave packets, particularly unstructured emissions and Pcl burst s at high latitudes, a triangular array of closely spaced induction ma gnetometers (similar to 150 km) was deployed beneath the average cusp projection during the 1992 Antarctic winter. From interstation time la gs the wave velocity and direction of arrival were calculated with ave rage uncertainties of +/-60 kms(-1) and +/-8 degrees. Wave sources wer e poleward of the array at low geomagnetic activity and equatorward at high activity. The sources also moved east to west with time, centred around local noon. These results are interpreted as indicative of the ionospheric signature of sources localized in the cusp, the low latit ude boundary layer (LLBL) or the outer magnetosphere. Intercalibration of the results for typical events with extrapolations of PACE radar o bservations and DMSP satellite particle signatures support sources wit hin these regions. Observed group velocities in the range 300-800 kms( -1) with a mean of 450 kms(-1) are consistent with wave propagation in the ionospheric waveguide. Signals above the waveguide lower cutoff f requency likely propagate away from the source in the ionospheric wave guide and across the magnetometer array. The results suggest a techniq ue for monitoring the high latitude boundary regions and outer magneto sphere using local ULF wave measurements.