Whistler observations of the plasmasphere/plasmapause from stations of the British Antarctic Survey

VLF whistler observations from Eights Station, Antarctica were crucial to the discovery and exploration of the plasmapause (''Carpenter's knee'') by Don Carpenter in the mid-1960s. The Weddell Sea sector of Antarctica is particularly well suited to such work because of the high whistler rate (conjugate to thunderstorm regions), proximity to the ground footprint of the average plasmapause, low electromagnetic noise levels (far from power lines, etc.), low ionospheric absorption (in winter), and wave amplification due to the South Atlantic Geomagnetic Anomaly. VLF recordings have been made at Halley, Antarctica, (76oS,27oW,L~4.3) since 1967; the station is located on a similar L-shell to Eights and its successor Siple, but eastward in longitude by about 2 h in magnetic local time. In this paper, we review some of the research on the structure and dynamics of the plasmasphere/plasmapause which has been based on whistler data from Halley. In particular, the use of Halley and Siple as a station pair corotating with the Earth through the Sun-Earth frame has enabled the complex dynamics of the duskside bulge region to be better understood. For example, features consistent with narrow dense sunward-pointing plasma tails, have been delineated. Whistler data from Halley have also provided much information on fine structure within the plasmasphere. The paper discusses some important results of inner plasmaspheric probing using fixed-frequency (~20kHz) whistler data from the lower latitude Faraday station (65oS,64oW,L~2.3), including annual density variations and magnetic storm effects, and concludes by indicating some directions for the future.

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