Magnetosphere simulations with ideal MHD, Hall MHD and the MHD with Adaptively Embedded Particle-in-Cell (MHD-AEPIC) models

The Magnetohydrodynamic with Embedded Particle-In-Cell (MHD-EPIC) model has been developed and applied successfully to Earth, Mercury, Mars and Ganymede magnetosphere simulations. While MHD-EPIC is many orders of magnitude faster than a fully kinetic global model, it can become prohibitively slow if the potential region of interest where kinetic phenomena, such as magnetic reconnection, can occur is large. This is due to the fact that the PIC domain in MHD-EPIC is restricted to a set of static Cartesian boxes. For example, a very large PIC box would be needed to accommodate the flapping motion of the magnetotail current sheet during a geomagnetic storm simulation. To tackle this problem, we have developed a new MHD with Adaptively Embedded Particle-In-Cell (MHD-AEPIC) model. MHD-AEPIC inherits all numerical algorithms from MHD-EPIC and incorporates a new adaptive PIC model, the Flexible Kinetic Simulator (FLEKS). FLEKS allows the PIC cells to be activated and deactivated during a simulation. The coupling between the MHD model and the adaptive PIC grid has been developed and implemented into the Space Weather Modeling Framework. We have also developed physics-based criteria to identify potential reconnection sites, which makes the adaptation fully automatic. In this work, we apply the new MHD-AEPIC model to a geomagnetic storm simulation and demonstrate how adaptation makes this simulation feasible. We compare MHD-AEPIC, Hall MHD and ideal MHD simulation results with each other and with observations ranging from electron scales to global scales. In particular, we demonstrate that MHD-AEPIC is capable of reproducing electron-scale physics in a global simulation.