Force-balanced Magnetospheric Structure with Thin Current Sheets

For many magnetospheric physics applications, force balance between the magnetic field and plasma pressure forces is essential. This study presents 3-D solutions for the magnetospheric structure in force balance with observed pressure distributions. The calculation is extended compared to previous work to include the high-latitude (open-field) magnetospheric region. We use several pressure distributions: either taken directly from observations (GEOTAIL pressure data in the plasma sheet and DMSP ionospheric pressure) or empirical (Spence-Kivelson formula on the Sun-Earth axis at midnight local time). The 3-D solutions are obtained by expressing the magnetic field in terms of Euler potentials and numerically solving the force-balance equation in a flux coordinate system. As computational boundary conditions we use magnetic flux surfaces obtained from the T96 empirical model. The numerical results are rich in physical content, and contain the cross-tail and Birkeland currents. By varying the boundary conditions and the pressure distributions, we investigate the change in magnetospheric structure under different external (IMF) conditions. In particular, we discuss the appearance of thin sheets of intense cross-tail current close to Earth (|X| < 10 R_E) during active times.