Longitudinal differences in electron precipitation near L = 4

Abstract

The differences in the electron precipitation characteristics as seen above Siple Station, Antarctica, and the Kerguelen Islands have been studied. These two sites are both in the southern hemisphere at nearly the same magnetic latitude (L=4). The two stations are at longitudes that place them roughly equal distances east and west of the center of the South Atlantic magnetic anomaly at this L value. With respect to the direction of electron drift, Siple is upstream of the anomaly, and Kerguelen is downstream. The primary data used in the study were counting rates from rocket‐borne, parachute‐deployed, sodium iodide scintillation counters at altitudes of 80 to 30 km and VLF wave data from both ground‐based and rocket‐borne receivers. Nine rocket flights are involved, five from Kerguelen and four from Siple. The flights were made under a range of geomagnetic and VLF activity conditions. The data differ in two major respects. First, the precipitation background at Kerguelen is very low, with high levels of wave activity being required to produce any detectable precipitation, an observation which indicates that there is a range of longitude and/or magnetic local time in which the electron pitch angle diffusion rate is 2 orders of magnitude lower than the long‐term global average rate. Second, X ray microbursts were found to be essentially absent at Kerguelen and very common at Siple. This observation appears to support models of the microburst generation process which predict maximum pitch angle scatterings of only a few tenths of a degree.