Two‐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 the model the continuity, momentum, and energy equations of a two‐ion (O + and H + ), quasi‐neutral, currentless plasma are solved along a closed geomagnetic field line; diffusive equilibrium is not assumed. Collisions between all stream pairs and with neutral species are included. The model includes a corotating, tilted dipole magnetic field and neutral winds. Ionospheric sources and sinks are accounted for in a self‐consistent 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 streams pass through each other practically unimpeded. When the streams approach the boundary in the conjugate ionosphere, a shock develops there, which moves upward and dissipates slowly; at about the same time a reverse shock develops in the hemisphere of origin, which moves upward. After about 1 hour, large shocks develop in each stream near the equator; these shocks move toward the equator and downward after crossing the equator. However, these shocks are probably artificial, because counterstreaming flows occur in each H + fluid, which the model can only handle by creating shocks.