LOW-ENERGY PLASMA IN EARTHS MAGNETOSPHERE

The low‐energy plasma fluxes in the earth's magnetosphere, with energies from thermal up to ∼50 kev, are an important factor in determining many of the essential properties of the magnetosphere. Currents produced by the motion of these charged particles play a key role in the development of magnetic storms and in the production of auroras and the geomagnetic tail. This paper will review the experimental observations of this plasma obtained over the last decade in different regions of the magnetosphere, considered in order of increasing distance from the earth. The similarity of results from measurements of the ion and electron components of the earth's thermal plasma envelope and the dependence of the altitude of the boundary of this envelope (the ‘plasmapause’) on geomagnetic activity are described. Within the radiation belts there exists a low‐energy plasma component that is much more variable than the energetic component; the variation of low‐energy plasma fluxes in the outer belt seems to be the main cause of geomagnetic storms. The radiation belts are always surrounded by low‐energy plasma fluxes; on the night side these fluxes become a part of the thick plasma layer within which is imbedded the neutral sheet of the geomagnetic tail. Experimental data on low‐energy plasma at geocentric distances >2 RE and geomagnetic latitudes >45° are very scarce; this region needs intensive investigation. Copyright © 1969 by the American Geophysical Union.