Improved Euler potential method for three-dimensional magnetospheric equilibrium

摘要

A new Euler potential method is presented for computing 3-D magnetospheric equilibria with prescribed plasma pressure, that significantly improves on a previous flux coordinate approach. In the new approach, the Euler potential α is no longer necessarily the magnetic flux, but can be specified much more freely, allowing equilibrium calculations in much more extended magnetospheric domains. With an empirical plasma pressure model as input and the T96 empirical magnetic field for boundary conditions, the new method is applied to compute a force balanced quiet time magnetospheric state extending to 30 R E in the magnetotail. While the force-balanced results for the magnetic field are not too different from T96 on the midnight axis, a very large discrepancy is found between field aligned currents (FACs) in the force balanced state and those computed from the empirical field and pressure using Vasyliunas equation; this shows that explicitly computed force balance is required for deriving FACs from plasma pressure and magnetic field by way of Vasyliunas equation.