On the large-scale distribution of magnetospheric currents and thermal plasma: Results from magnetic field models and observations


The author presents 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. He first presents a brief history of magnetic field models of the Earth's magnetosphere. He then discuss related work on magnetotail plasma pressure. In the first study, he develops a technique for obtaining pressure gradients and anisotropies consistent with quasi-static equilibrium from recent empirical magnetic field models. He finds that the near-tail magnetic stresses can be balanced by a nearly isotropic plasma pressure with a realistic equatorial gradient. In the second study, he surveys plasma pressures observed near the midnight meridian. He finds 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. He reassess the convection model and finds that observed quiet time pressure profiles can be reproduced so long as he accounts for the finite tail width. In the next main section, he presents 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.



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