Modeling Observed Plasma Sheet Asymmetries During Intervals of Northward Interplanetary Magnetic Field

We apply a Lorentz force particle tracing code to investigate observed asymmetries and other features in the averaged plasma sheet parameters obtained from Geotail observations. Our study focuses on intervals of northward interplanetary magnetic field (IMF), which play an important role in pre-conditioning the plasma sheet for more active times. We are primarily concerned with the variations in the phase space densities with respect to the GSM Y axis, such as dawn-dusk asymmetries and the differences between flank and midnight populations. We have developed a plasma transport model that computes the drift trajectories of particles in the magnetosheath and magnetosphere using the relativistic Lorentz force equation. For our magnetic field, we combine an observation-based Tsyganenko magnetospheric magnetic field model with a theoretical magnetosheath magnetic field model that we have developed. Our electric field is obtained by tracing the potential along magenetic field lines (assumed to be equipotentials) to either the unshocked solar wind (where the electric field is assumed uniform) or the ionosphere (where we specify a Weimer potential). Our model is used to trace the drift paths of plasma sheet particles of different energies backward in time to estimate their source locations and thereby explain observed features of the plasma sheet. The limitations of the model are examined in order to assess the potential role that non-modeled processes could play in the particle transport and their potential impact on the results.