Embedding particle-in-cell simulations in global magnetohydrodynamic simulations of the magnetosphere

We have combined global magnetohydrodynamic (MHD) simulations of the solar wind and magnetosphere interaction with an implicit particle-in-cell simulation (PIC) and used this approach to model magnetic reconnection at both the dayside magnetopause and in the magnetotail plasma sheet. In this approach, we first model the magnetospheric configuration driven by the solar wind using the MHD simulation. At a time of interest (usually when a thin current sheet has formed in the MHD simulation), we load a large particle-in-cell simulation with plasma and fields based on the MHD state. We use the MHD results to set the boundary conditions on the PIC simulation. The coupling between the two models is one way - the PIC results do not change the MHD results. In these calculations, we use the UCLA global MHD code and the iPic3D implicit particle-in-cell code. In this paper we describe this technique in detail. As an example of this approach, we present PIC results on reconnection in the magnetotail during a magnetospheric substorm.