Abstract
The Earth's plasmasphere, discovered some 50 years ago using ground based radio techniques, is a torus-like region that encircles the Earth. Its outer boundary, called the plasmapause, is aligned with the Earth's dipole magnetic field, typically reaching an equatorial distance of 4 Earth radii. The plasmapause region exhibits many dynamic effects, including fast inward displacements during storm-like intervals in space, instabilities, and complex wave activity. The storm-time displacements are believed to be due to the physics of interactions between the cooler plasmas of the plasmasphere and the hot plasmas that move inward toward the Earth during stormy periods. Much that we know about the plasmasphere has been accomplished through remote sensing. For example, teams of researchers on the IMAGE satellite, launched in March 2000, have been studying the plasmasphere using a variety of imaging techniques, including radio sounding. Some remarkable results from the IMAGE mission will be described.