Investigating Particle Acceleration in the Magnetotail by Combining Large Scale Kinetic and Particle in Cell Simulations
Abstract:Over the past several years we have used Large Scale Kinetic (LSK) simulations in which the trajectories of millions of test particles are calculated in the electric and magnetic fields from a global magnetohydrodynamic (MHD) simulation of the solar wind, magnetosphere and ionosphere system to evaluate the effects of the large scale fields on particle motion and dynamics. By collecting the particles at “virtual detectors” placed throughout the magnetosphere we can get direct comparisons between the simulation results and observations. The LSK calculations, though not self-consistent, are a powerful tool for determining the effects of the large scale fields. Recently we have developed a new technique in which we model magnetospheric dynamics by using an implicit particle in cell simulation (iPIC3D) code in which the initial and boundary conditions are determined by the global MHD model. This provides a self-consistent calculation of particle dynamics including waves and instabilities not included in MHD.
We have applied the MHD plus PIC approach to a substorm on February 15, 2008. In the magnetotail we found that a series of dipolarizations formed due to unsteady reconnection. We also found that the largest electron acceleration occurred in the separatrices far from the x-point. We attributed the acceleration to a streaming instability in the separatrices. To further evaluate the acceleration mechanisms operating in this substorm we have applied the LSK technique to the electric and magnetic fields from the PIC simulations. Electrons are already included in the PIC simulation, but the LSK simulations will allow many more to be followed and analyzed. We will use the results to evaluate acceleration mechanisms in the PIC results and will present a comparison of LSK results in the MHD fields with those from the PIC fields.