Abstract
Data from the VLF receivers aboard the Alouette and Isis spacecraft contain a number of examples of the ‘saucer’ radio phenomenon, so named because of its hyperbolic shape in the amplitude-frequency-time displays. These have been interpreted in terms of a model involving a small source of emission. Frequency-time signatures have been calculated by using a ray-tracing program assuming that the appropriate dispersion curves are those of the whistler mode on its resonance cone surface. Spatial dimensions of the sources have been deduced: typically, these are 0.5 km horizontally by no more than 10 km vertically. Total power radiated is about 10 mW. In the model, suprathermal electron beams flow through the source region and engage in an instability with background electrons. The deduced source dimensions are consistent with quantitative predictions of beam-plasma theory.
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