The overall flow of MHD-PIC coupling. At t = 0 the MHD code sends the MHD state inside and around the PIC region to the PIC code. Both the MHD and PIC codes then advance by one or more time steps until both models reach the next coupling time. Information is exchanged both ways, but this time the PIC code only uses the MHD solution as a boundary condition, while the MHD code overwrites its solution in the PIC region with the PIC solution. This process continues until they reach the final simulation time or until the PIC region is removed (after Daldorff et al., 2014).