Two-Dimensional Reconstruction of Magnetic Mirror Structures With Pressure Anisotropy: Theory and Application

摘要

A new reconstruction method is developed for two-dimensional (2-D), steady, magnetohydrostatic structures with anisotropic plasma pressure, which is assumed to be solely dependent on magnetic field strength. This dependence leads to a Poisson-like partial differential equation that can be solved as a spatial initial-value problem by use of data taken from a single spacecraft passing through a coherent structure. However, the resulting partial differential equation cannot be reduced to the ordinary Grad-Shafranov equation with isotropic pressure. The numerical code for new reconstruction is developed and successfully validated against an exact analytical solution. This new reconstruction method is first applied to examine 2-D geometry of magnetic mirror structures observed by the Magnetospheric Multiscale (MMS) spacecraft in the Earth's magnetosheath. The observed mirror structures satisfy the magnetohydrostatic conditions and are comoving with the average ion bulk flow. Using MMS1 measurements, the reconstruction produces a 2-D magnetic field map and distribution maps of pressures perpendicular and parallel to the magnetic field. The reconstructed field map reveals magnetic bottle-like structures as predicted by the mirror-mode theory. A very good agreement is achieved between observation and reconstruction for the other three MMS spacecraft not used for reconstruction. It is concluded that this new reconstruction is suitable for examining 2-D geometry of mirror structures.