The plasmasphere

The outermost region of the ionosphere is the plasmasphere. It is a region of dense, cold plasma that surrounds the Earth. Although plasma is found throughout the magnetosphere, the plasmasphere usually contains the coldest plasma.

The electrons in plasma gain more energy, and they are very low in mass. They move along Earth's magnetic field lines and their increased energy is enough to escape Earth's gravity.

As more and more electrons begin to escape outward, they leave behind a growing net positive electric charge in the ionosphere and create a growing net negative electric charge above the ionosphere; an electric field begins to develop. Very quickly this resulting electric field opposed upward movement of the electrons out of the ionosphere. Τhe ions react to the electric field and are attracted to it. They begin to move upward out of the ionosphere too.

For a planet like Earth with a strong planetary magnetic field, these outward moving particles remain trapped near the planet unless other processes further draw them away and into interplanetary space. As is always the case with nature, there is much more story to tell about this "upwardly mobile" plasma and these other processes.

Over only a short time period of hours and days this escaping plasma can, in some places, build up in concentration until an equilibrium is reached where as much plasma flows inward into the ionosphere as flows outward.

This "donut shaped" region of cold (about 1 electron volt in energy) plasma encircling the planet is called the plasmasphere.

Generally, that region of space where plasma from the ionosphere has the time to build up to become identified as the plasmasphere rotates or nearly rotates with the Earth. That region shrinks in size with increased space weather activity and expands or refills during times of inactivity.

As it shrinks with increasing activity, some of the plasmasphere is drawn away from its main body (plasmaspheric erosion) in the sunward direction toward the boundary in space between that region dominated by Earth's magnetic field and the much larger region dominated by the Sun's magnetic field. This process is demonstrated in the video released by BIRA where the dynamic kinetic model of the plasmasphere is explained. The BIRA research group is planning to make available the results of this model in PITHIA-NRF, with open access.

The plasmasphere is a region in the space environment of the earth where electrons, protons and helum-ions are trapped in the terrestrial magnetic field. (Credits: BIRA-ASB)

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