On the cause of approximate pressure isotropy in the quiet near-Earth plasma sheet

摘要: In this paper we attempt to provide a theoretical explanation of the observed approximate pressure isotropy in near-earth geomagnetic tail We first give new formulation self-consistent theory two-dimensional anisotropic steady states by generalizing Grad-Shafranov equation. Then it is shown that anisotropy-driven instabilities, active midplane plasma sheet, lead highly isotropic tensors for entire sheet. The key point due weakness magnetic field instabilities require only small anisotropy be excited. approach based on assumption an originally unstable system evolves into state. An order magnitude analysis supplemented and confirmed numerical example.