EMPIRICAL MODELING OF THE QUIET TIME NIGHTSIDE MAGNETOSPHERE

Empirical modeling of plasma pressure and magnetic field for the quiet time nightside magnetosphere is investigated. Two models are construc ted for this study. One model, referred to here as T89R, is basically the magnetic field model of Tsyganenko (1989) but is modified by the a ddition of an inner eastward ring current at a radial distance of simi lar to 3 R(E) as suggested by observation. The other is a combination of the T89R model and the long version of the magnetic field model of Tsyganenko (1987) such that the former dominates the magnetic field in the inner magnetosphere, whereas the latter prevails in the distant t ail. The distribution of plasma pressure, which is required to balance the magnetic force for each of these two field models, is computed al ong the tail axis in the midnight meridian. The occurrence of pressure anisotropy in the inner magnetospheric region is also taken into acco unt by determining an empirical fit to the observed plasma pressure an isotropy. This effort is the first attempt to obtain the plasma pressu re distribution in-force equilibrium with magnetic stresses from an em pirical field model with the inclusion of pressure anisotropy. The inc lusion of pressure anisotropy alters the plasma pressure by as much as a factor of similar to 3 in the inner magnetosphere. The deduced plas ma pressure profile along the tail axis is found to be in good agreeme nt with the observed quiet time plasma pressure for geocentric distanc es between similar to 2 and similar to 35 R(E).