The flux of X rays and ultraviolet radiation from the sun that is absorbed in the upper atmosphere breaks up molecules into electrically charged ions and electrons that are heated in the process to temperatures over a thousand degrees. This hot "plasma" expands and would escape the earth except that the charged particles are confined by the earth's magnetic field. Where the field lines are closed, which is out to about four earth radii in the equatorial regions, a relatively high density of hot plasma fills the volume, called the "plasmasphere." The plasmasphere extends about 60o in latitude towards the poles. In the earth's polar caps the field lines are open and the plasma escapes upward, and some is lost from the earth, but some, while still in the "tail" on open field lines in the larger "magnetosphere" is energized by electric fields due to a boundary effect of the passing supersonic solar wind. Some of this more highly energized terrestrial plasma then returns down the field lines and produces the spectacular aurora, and more heating in the polar upper atmosphere. This award is for theoretical studies in several topics connected with plasma dynamics in the plasmasphere and magnetosphere.
