2-STREAM MODELING OF PLASMASPHERIC REFILLING

Plasmaspheric refilling on an L = 4, flux tube was studied by using a time-dependent, hydrodynamic plasmaspheric flow model in which the ion streams from the two hemispheres are treated as distinct fluids. In t he model the continuity, momentum, and energy equations of a two-ion ( O+ and H+), quasi-neutral, currentless plasma are solved along a close d geomagnetic field line; diffusive equilibrium is not assumed. Collis ions between all stream pairs and with neutral species are included. T he model includes a corotating, tilted dipole magnetic field and neutr al winds. Ionospheric sources and sinks are accounted for in a self-co nsistent manner. Electrons are assumed to be heated by photoelectrons. The model flux tube extends from 200-km altitude in one hemisphere to 200-km altitude in the other hemisphere. Initially, the upwelling str eams pass through each other practically unimpeded. When the streams a pproach the boundary in the conjugate ionosphere, a shock develops the re, which moves upward and dissipates slowly; at about the same time a reverse shock develops in the hemisphere of origin, which moves upwar d. After about 1 hour, large shocks develop in each stream near the eq uator; these shocks move toward the equator and downward after crossin g the equator. However, these shocks are probably artificial, because counterstreaming flows occur in each H+ fiuid, which the model can onl y handle by creating shocks.