Plasma Distribution Solver: A Model for Field‐Aligned Plasma Profiles Based on Spatial Variation of Velocity Distribution Functions

Abstract

AbstractThis paper describes the plasma distribution solver (PDS), a theoretical model that determines plasma number density and pressure profiles along a magnetic field line of magnetized planets. The PDS computes velocity distribution functions of each particle species at an arbitrary point along a field line to meet the force balance and the accessibility. The number density, mean flow velocity, and pressure calculated by taking the zero‐th, first‐, second‐order moments of the velocity distribution functions enable us to obtain field‐aligned profiles of the quantities strictly consistent with the assumed ionospheric/magnetospheric boundary conditions. The spatial distribution of physical quantities, such as Alfvén speed and plasma β, was also obtained from the PDS results. We applied the PDS to the Jupiter‐Io system. When the temperature anisotropy is presented for the ion species originated from Io, the ion species other than protons, especially O+, can hardly reach mid‐to‐high latitudes. The number density of electrons which satisfy the charge neutrality with ions is also reduced compared to the case when the temperature is assumed to be isotropic. From these differences in the number density profile, we found the change of the boundary position, which characterizes dispersive Alfvén waves from the relation between the plasma β and the mass ratio between electrons and ions.