| We present the results of studies using magnetic field models and observations to determine, as a function of magnetic activity, the distributions of plasma pressure in the Earth's magnetic tail and to characterize field-aligned currents globally. We first present a brief history of magnetic field models of the Earth's magnetosphere. We then discuss related work on magnetotail plasma pressure. In the first study, we develop a technique for obtaining pressure gradients and anisotropies consistent with quasi-static equilibrium from recent empirical magnetic field models. We find that the near-tail magnetic stresses can be balanced by a nearly isotropic plasma pressure with a realistic equatorial gradient. In the second study, we survey plasma pressures observed near the midnight meridian. We find that vertical pressure balance is maintained between lobe magnetic and plasma sheet plasma pressure and that observed and model-derived pressures are consistent. The combined model-derived and observed pressure profile falls off more slowly than it would if established by a two-dimensional, adiabatic, lossless convection model. We reassess the convection model and find that observed quiet time pressure profiles can be reproduced so long as we account for the finite tail width. In the next main section, we present studies on the distribution of field-aligned currents (FACs). First, empirical magnetic models are used to determine the average FACs flowing in the magnetosphere as a function of geomagnetic activity. When mapped to the ionosphere, FAC systems with region 1 polarity both on the day side (DR1) and the night side (NR1) can be identified; a low-level, region 2-sense system (NPC) flows poleward of the NR1 system. The DR1 and NR1 FACs respond differently to geomagnetic activity and map to separated source regions. In order to compare the model-derived FACs with observations, we undertook an analysis of low-altitude MAGSAT data. The dynamics of the region 1 and 2 and "NBz" FACs emerge from the analysis. However, large-scale, organized FACs are obscured for AE... |
