Morphology of keV-electrons in the earth's magnetosphere as observed by GEOS 1

A study of the morphology of keV electrons in the earth's magnetosphere, between L = 4 and 8 and from 4 to 21 hours local time, as observed by GEOS-1 from May to December 1977 is reported. The data are analyzed to yield energy flux, and by fitting with multi-Maxwell distributions, to give densities and temperatures along two pitch-angle directions, 90 and 15 deg. It is shown that 83 percent of the data can be successfully fitted with a two-temperature Maxwell distribution function, and that the temperatures do not vary much, compared to the densities which vary strongly with the activity level and with the local time. The ratio of low to high energy density remains roughly constant, indicating that the two populations are interdependent. The statistical data do not fit well with Maxwellian distributions and also show an increase in the density, at L = 6 to 7 in the afternoon hours, which may be connected with the fact that the majority of the data are collected close to the geomagnetic equator.