High-latitude ionization spikes observed by the POGO Ion, Chamber Experiment

Abstract

The POGO spacecraft was launched into a low polar orbit October 14, 1965, and carried an ion chamber experiment sensitive to electrons with energies greater than 1 Mev and protons greater than 10 Mev. Ionization ‘spikes’ appearing frequently at high latitudes were studied in detail. These spikes were found to be present near the high-latitude boundary of stably trapped radiation on at least 30% of the satellite passes through this region. Their frequency of occurrence increases markedly with increased magnetic disturbance. Occurrence of those spikes lying just inside the observed boundary of trapping appears to be evenly distributed with respect to local time, but the occurrence of spikes at latitudes outside the region of stable trapping is predominantly in the dawn hemisphere. We argue that these spikes are the result of injection of high-energy electrons (E ∼ 1 Mev) onto field lines near the boundary of trapping and are associated with the electron ‘islands’ reported in the magnetospheric tail by Anderson and others. We show that the spatial distribution of spikes as observed by POGO should be expected as a consequence of electron drift, in the post-midnight quadrant, into a region of pseudotrapping.