LOW-FREQUENCY IMPULSIVE AURORAL HISS OBSERVATIONS AT HIGH GEOMAGNETICLATITUDES

Wave receivers in Antarctic Automatic Geophysical Observatories (AGOs) measure spectral features of low-frequency impulsive auroral hiss emi ssions which cannot be observed at northern hemisphere sites or near m anned Antarctic stations due to man-made interference. From observatio ns at AGO-P1 (similar to 80 degrees invariant latitude) we distinguish two spectral types of LF impulsive auroral hiss: normal events, in wh ich the power spectral density is a decreasing function of frequency t hroughout the LF band, presumably peaking in the VLF band below the fr equency range of the LF/MF/HF receiver; and LF cutoff events, for whic h the power spectral density peaks in the LF band with little or no po wer at VLF. Out of a large sample of impulsive auroral hiss events obs erved at AGO-P1, 64% are the normal type, 14% are the LF-cutoff type, and 22% are a mixture of both. A hiss propagation model similar to tha t of Makita [1979] was used to evaluate approximately whether the obse rved occurrence statistics of LF cutoff auroral hiss are consistent wi th previous models of auroral hiss generation and propagation. The res ults indicate that LF cutoff auroral hiss can be explained by propagat ion effects and suggest that the observed LF cutoff occurrence statist ics are consistent with LF impulsive auroral hiss originating at or du cted to altitudes of 2000-5000 km.