The plasmasphere, or inner magnetosphere, is a region of the Earth's magnetosphere consisting of low energy (cool) plasma. It is located above the ionosphere. The outer boundary of the plasmasphere is known as the plasmapause, which is defined by an order of magnitude drop in plasma density.
Traditionally, the plasmasphere has been regarded as a well behaved cold plasma with particle motion dominated entirely by the geomagnetic field and hence corotating with the Earth. In contrast, recent satellite observations have shown that density irregularities such as plumes or biteouts may form. It has also been shown that the plasmasphere does not always co-rotate with the Earth.
See also 
The plasma of the magnetosphere has many different levels of temperature and concentration. The coldest magnetospheric plasma is most often found in the plasmasphere, a donut-shaped region surrounding the Earth's middle. But plasma from the plasmasphere can be detected throughout the magnetosphere because it gets blown around by electric and magnetic field
- Carpenter, D. L., Whistler evidence of a 'knee' in the magnetospheric ionization density profile, J. Geophys. Res., 68, 1675–1682, 1963.
- Nishida, A., Formation of plasmapause, or magnetospheric plasma knee, by combined action of magnetospheric convections and plasma escape from the tail, J. Geophys. Res., 71, 5669, 1966.
- Sandel, B. R., et al., Extreme ultraviolet imager observations of the structure and dynamics of the plasmasphere, Space Sci. Rev., 109, 25, 2003.
- NASA web site
- University of Michigan description
- University of Alabama in Huntsville research
- Southwest Research Institute description
- IMAGE Extreme Ultraviolet Imager
- EUV Images of the plasmasphere
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