Modeling the inner plasma sheet protons and the magnetic field

In order to understand plasma sheet dynamics during quiet and disturbed times, we incorporate a modified version of the Magnetospheric Specification Model with a modified version of the Tsyganenko 96 magnetic field model to self-consistently simulate protons and magnetic fields under convection electric fields corresponding to different solar wind energy inputs. The local-time dependent proton differential fluxes assigned to the model outer boundary are a mixture of plasma from the mantle and from the low latitude boundary layer. We first used this model to simulate the plasma sheet under weak convection corresponding to a cross polar-cap potential drop (DeltaФ PC) equal to 26 kV and with one-dimensional force balance. This simulation obtained quiet time equilibrium for protons and the magnetic field that agree well with observations. We then extended force balance to two-dimensions along the midnight meridian and the results yielded improved agreement with observations, an improvement resulting from the coupling between plasma and the magnetic field being more accurately modeled. In order to evaluate the evolution of the inner plasma sheet under enhanced convection, we increased DeltaФ PC steadily from 26 kV to 146 kV over 5 hours. Our simulation accounts for the observed changes in the plasma sheet from quiet to moderate activity (which we take to be DeltaФPC = 98 kV) both qualitatively and quantitatively, which indicates the plasma drift is the major contributor to plasma transport and energization in the plasma sheet. For high activity (DeltaФPC = 146 kV), we obtained good qualitative agreement with observations, however, we underestimated the observed pressure and temperature by a factor of ∼2. This disagreement could be due to important effects, such as solar wind dynamic pressure enhancement and activity dependent particle sources, that are not yet included in the simulation. The magnetic field lines become more stretched as convection is enhanced. Our simulation shows that the plasma sheet resulting from drift transport is far from possible force balance inconsistency, and that the diamagnetic drift and self-consistent magnetic fields play important roles in restraining pressure increase. A scale analysis of our results shows that the frozen-in condition E = -vxB is not valid in the inner plasma sheet.