Rocket investigations of electron precipitation and VLF waves in the Antarctic upper atmosphere

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The two Antarctic rocket campaigns conducted by American scientists during the past 10 years are described, and the results of these efforts are reviewed. Although the primary objective of both campaigns, the observation of precipitating electrons triggered by the Siple VLF transmitter, was not achieved, significant advancements in understanding upper atmosphere phenomena were made. Standing wave patterns in the ionosphere were observed for the first time by wave experiments flown aboard Nike‐Tomahawk rockets. The same detectors were able to monitor a continuous signal from the transmitter through the neutral atmosphere and into the ionosphere. This in situ observation of a radio wave traversing a neutral and a plasma environment provided unique data for comparison to theoretical studies of wave propagation. SuperArcas measurements provided two distinct types of energetic electron precipitation data: one type was continuous on the time scale of > 1 min, and the other was in X ray microbursts created by bursts of energetic electrons stopping in the upper atmosphere with durations < 1 s. The burst data were compared to theoretical models of wave‐particle interactions. The observations of continuous electron precipitation with sufficient energy to penetrate the atmosphere to an altitude of 60–80 km were found to be consistent with a model of electron transport from the trapped population to the atmosphere in which gradient and curvature drift in the drift cone plays a principal role. The model requires slow electron pitch angle diffusion of the geomagnetically trapped population and predicts that almost all energetic electron precipitation occurs in the South Atlantic Anomaly. The electron precipitation model is shown to organize all of the SuperArcas data, which include not only measurements at Siple Station, Antarctica, but also those at Kerguelen, another L = 4 location in the southern hemisphere, and at northern locations at higher latitudes. A prediction of the model which involves the effect of the dawn‐to‐dusk convection electric field on energetic electron precipitation is described: diurnal modulation is predicted with the maximum electron precipitation intensity when the South Atlantic Anomaly is at local dawn. A test of this prediction made by SuperArcas flights in 1981 provided support for the slow diffusion model. The SuperArcas results on energetic electron precipitation are shown to disagree with a satellite result at L = 4 which requires fast diffusion. Reasons for the discrepancy between the two data sets are discussed, and steps which could be taken to resolve the apparent controversy are suggested. Finally, the suggestion is made that the two rocket campaigns conducted by American scientists in Antarctica during the past decade be regarded as a feasibility study leading to an active rocket research program in Antarctica for the remainder of the century.