We use the global MHD code Grand Unified Magnetosphere Ionosphere Coupling Simulation (GUMICS-4) to simulate the location and motion of the magnetospheric cusp and the subsolar magnetopause under various interplanetary magnetic field (IMF) directions and solar wind dynamic pressures. We identify the cusp in the simulation from the location of the open/closed field line boundary (OC boundary, equatorward edge of the cusp), determined by direct field line tracing, and several MHD parameters that axe expected to react to the entry of the magnetosheath fluid. These parameters include the location of the maximum internal energy density and maximum diamagnetic depression and are collectively called the plasma proxies of the cusp. The simulation results show that with increasingly southward IMF the OC boundary and the plasma proxies move equatorward, as expected. During northward IMF, however, the plasma proxies are located equatorward of the OC boundary and thus on closed field lines. The GUMICS-4 OC boundary location and the statistical plasma cusp location from Polar satellite observations are in good quantitative agreement during southward IMF, but during northward IMF the observed cusp is again several degrees equatorward from the simulated OC boundary. Therefore we conclude that during northward IMF the cusp identification from either the OC boundary or the plasma proxies may become problematic in MHD simulations and discuss the possible physical reasons. The simulation results further indicate that increasing solar wind dynamic pressure shifts the high-altitude cusp slightly equatorward. Furthermore, the increasing pressure also pushes the magnetopause clearly earthward, as expected, while the same field line in the ionosphere shifts only slightly equatorward, implying changes in the field line shape as the pressure changes. In other respects, the simulated magnetopause is in quantitative agreement with the empirical model of Shue et al. .
|Number of pages||16|
|Journal||Journal of Geophysical Research|
|Publication status||Published - 1 Dec 2001|
|MoE publication type||A1 Journal article-refereed|
- INTERPLANETARY MAGNETIC-FIELD
- MAGNETOSPHERIC CUSPS
- POLAR CUSP