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This paper considers the spatial extent and the spectral index of spike events in auroral radio absorption observed with riometers. On the evidence of narrow‐ and wide‐beam observations at more than one radio frequency and satellite particle data, it is shown that the typical spike event extends for only tens of kilometers in the ionosphere, compared with several hundred kilometers for auroral absorption in general. The spectral index is found to be close to 2.0, as for the general absorption, implying that the spike absorption is not produced at an unusually low altitude. It is concluded that for spike events the electron precipitation is very intense, is not unusually energetic, and is spatially restricted.

Cosmic noise absorption records for a period of more than one year from the South Pole have been analyzed using a standard ‘event report.’ There are two major regions in the diurnal pattern of absorption activity, a magnetic‐night group and magnetic‐day group. The night events tend to be more intense but of shorter duration than the day events, and there is a progressive decrease of intensity during both the day and night groups. These diurnal changes probably correspond to changes in the properties of the energetic particles entering the atmosphere, and these effects are clearly independent of local solar illumination conditions. In a subsequent paper these results will be compared with those from the conjugate station, Frobisher Bay.

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