Hybrid modeling of the interaction between the solar wind and planets

Mats Holmström
Swedish Institute of Space Physics
Kiruna, Sweden


A hybrid plasma solver treats ions as particles and electrons as a fluid. Here we present a hybrid solver for the interaction between the solar wind and planets, with a focus on numerical issues. A key component of such a model is the treatment of the region in and near the obstacle to the plasma flow. The presented solver can handle low density regions, fixed background fields, obstacles with internal resistivity, and arbitrary ion production functions. Ions that hit the obstacle are removed from the simulation. In the wake behind the object there are low density regions that can cause numerical instabilities. The interior of the obstacle can have spatially variable resistivity. Both low density regions and the interior of the obstacle are handled by solving a magnetic diffusion equation. Some objects have permanent magnetic fields. Either dipole fields, e.g., Earth and Mercury, or localized crustal fields, e.g., the Moon and Mercury. These are handled as a fixed background field. Care has to be taken so that the background field is divergence free. The parallel solver is implemented in the FLASH open source software framework.