Rebounding Plasma Flows in the Inner Magnetosphere

Substorms send jets of plasma careening Earthward at speeds near 600,000 miles/hour. Researchers comparing multipoint THEMIS spacecraft observations with the predictions of numerical simulations have determined the width of one such jet and determined what happened to it when it encountered the strong magnetic fields within the inner magnetosphere. Plasma jets with the width of the Earth slam into the inner magnetosphere, generating vortices with opposite senses of rotation that appear and disappear on either side of the plasma jet. These vortices become sources of field-aligned electrical currents that flow down to the Earth's ionosphere, where they generate auroral brightenings and intense magnetic field disturbances. After striking the inner magnetospheric magnetic field, the plasma jet itself bounces back and forth, losing energy each time it encounters the magnetic field, and continuing to oscillate until the flow energy is dissipated in the form of plasma heating.