The outer plasmasphere as a source of magnetospheric plasmas.

摘要

In this dissertation, we consider the supply of outer plasmaspheric plasma to the magnetosphere by means of both global convection modeling and analysis of spacecraft measurements of low-energy ions. First, the convective evolution of the plasmasphere is studied using a dynamic global core plasma model (DGCPM) that includes the influences of spatially and temporally varying convection and refilling processes to calculate the equatorial core plasma density distribution throughout the inner magnetosphere and magnetopause boundary layer regions. An expression for the electric field structure within subauroral ion drift (SAID) features is developed based on observations. It is found that ionospheric subauroral ion drift type convection electric fields in the predusk to midnight sectors, when mapped to the ionosphere, lead to the formation of a density trough embedded in the plasmasphere, provided that the SAID electric field crosses the plasmapause. In a second investigation, a statistical study of brief intervals of cold dense plasma in the midnight sector is undertaken using data from the Los Alamos Magnetospheric Plasma Analyzer (MPA) onboard geosynchronous satellite. The analysis suggests that premidnight cold plasma encounters at geosynchronous orbit most likely arise through corotation-dominated transport of dayside plasmaspheric structures into the premidnight sector. In a third investigation, a model of electric and magnetic field structures in the outer dayside magnetospheric regions is incorporated into the DGCPM to examine the loss of plasmaspheric-origin plasma into the magnetopause boundary layer and the convection of this plasma that remains trapped on closed field lines. The model predicts that plasmaspheric plasma reaching the outer magnetosphere is diverted anti-sunward along the outer flanks of the magnetosphere. The calculated He{dollar}sp+{dollar} densities in the magnetospheric boundary layer regions are consistent with the limited number of observations of He{dollar}sp+{dollar} densities in that region.