Some observational phenomena are well reproduced by our global MHD while others are not: remarks on what, why and how Original Research Article

We address the question of what features our recent global magnetohydrodynamic (MHD) simulations of the ionosphere-magnetosphere system reproduces well, what not so well, and where the problem areas generally lie in the MHD framework. We show that features which depend on the conservation of mass, momentum or energy, or which involve a balance of forces, are generally reproduced well. The magnetopause position is a typical example. On the other hand, features which depend on different parallel/perpendicular physics, or on the existence of multiple temperatures, are badly reproduced. Unfortunately, many important near-Earth phenomena like auroral acceleration fall in this category. We also discuss some numerical method specific problems: In the Yee-mesh scheme, the upstream leakage of the magnetic field may become a problem, while the volume average schemes usually require an elliptic solver to reduce the divergence of the magnetic field.