Three-dimensional magnetospheric structures and energetic particle injections

Abstract

This thesis addresses two topics. The first topic is finding numerical solutions to the 3-D “quasi-static” equilibrium problem in the magnetosphere. By expressing the magnetic field in terms of Euler potentials and choosing a proper flux coordinate system, the 3-D force balance equation between magnetic field and plasma pressure forces is de-composed into two “quasi-2D” elliptic equations, which are solved (with prescribed boundary conditions and pressure distributions) by an iterative method. The current study presents significant physical improvements compared to previous work on 3-D magnetospheric equilibria in flux coordinates; these include, among others, the relaxation of the condition that the pressure P be constant on the magnetic flux surface, expanded realistic flux boundaries (taken from empirical magnetic field models) and pressure profiles (based on satellite measurements), as well as the extension of the 3-D equilibrium approach to “open-field” magnetospheric regions. Using a wide range of boundary conditions and pressure distributions allows us to obtain the state of the magnetosphere under various solar wind conditions. Our findings from the modeled high-β equilibria include the formation of both Region-1 and Region-2 Birkeland currents on closed magnetic field lines, as well as the appearance of a “thin” cross-tail current sheet with enhanced current in the near-Earth region during the substorm growth phase.

The second topic of the thesis consists of simulating energetic particle “injections” often observed by satellites at geosynchronous orbit in connection with magnetospheric substorms. In order to understand these injections, a physical model of time-dependent electric and magnetic fields is proposed, which determines the particle trajectories in analytical form. A numerical code is then developed in order to compute the injected particle fluxes at different satellite locations. The computed flux values agree well with the ones from satellite observations. A major result of our work is the fact that the particles “injected” at geosynchronous orbit arrive from an initial location of less than 10 R_E from Earth, a finding with important consequences for substorm onset studies. The project is also very significant in the context of the Space Weather research program, designated to ensure protection of vulnerable space-borne technological apparatus.