Review of hot plasma composition near geosynchronous altitude

The information available on the hot plasma composition at and near the geostationary satellite orbit has increased dramatically during the past four years. At energies below 32 keV, ions of terrestrial origin, 0(+) and He(+) are frequently observed to be significant contributors to the hot plasma density and energy density, and during geomagnetically disturbed periods, 0(+) ions are typically the dominant hot plasma ions. Evidence for a solar cycle dependence to the 0(+) hot plasma densities at the geostationary orbit has been found. Our understanding of the details of the physical processes involved in the entry, acceleration, transport, and loss of the plasma ions, and thus our ability to model them, is still quite limited.