A statistical analysis of the low-energy geosynchronous plasma environment

This is the second of two papers which together provide a detailed statistical analysis of the low-energy (1-eV to 100-keV) geosynchronous plasma environment. In this paper, data on the ion environment between approximately 1 eV and 80 keV are statistically analysed. About 50 days of 10-min averages of the first 4 moments of the ion distribution function from the University of California at San Diego low-energy plasma detectors on the ATS-5 and ATS-6 geosynchronous satellites are studied in terms of: occurrence frequency, local time variations, Ksub(p) variations, injection events, and intercomparisons among the 4 moments. Variations in the 4 moments can be explained by assuming the existence of 2 dominant plasma populations upon which are superimposed plasma injection events. In conjunction with this analysis, the accuracy of the 4-moment representation for ions was tested and, unlike that for electrons, found to be limited by the energy band-pass of the instrumentation and by a lack of knowledge of the angular anisotropies and ionic composition. Even so, these limitations are outweighed by the utility and compactness of the method. (author)