THE LIMIT OF SIMULATIONS. “On the other hand, their use still has serious limitations, both due to missing physics especially in the ionosphere and in the inner magnetosphere, and due to the limitations of the MHD approach in describing the collisionless, multicomponent plasmas in the magnetosphere.” (MHD = Magnetohydrodynamics).
https://link.springer.com/article/10.12942/lrsp-2007-1