Distribution of electron densities in the Earth's plasmasphere

A new empirical model of the plasma density in the plasmasphere is presented and validated in this dissertation, along with several case studies of asymmetrical plasmasphere and two-dimensional density distributions. This empirical model is based on more than 700 density profiles along field lines derived from active sounding measurements made by the radio plasma imager (RPI) onboard the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite between June 2000 and July 2005. The measurements cover all magnetic local times and vary from L = 1.6 to L = 4 spatially, with every case manually confirmed to be within the plasmasphere by examination of the corresponding dynamic spectrogram. The resulting model depends not only on L-shell but also on magnetic latitude and can be applied to specifying the electron densities in the plasmasphere between 2000-km altitude and the plasmapause. It consists of two parts: the equatorial density, which falls off exponentially as a function of L-shell; and the field-aligned dependence on magnetic latitude and L-shell (in the form of invariant magnetic latitude). The fluctuations of the density in a given location in space appear to be greater than what could be explained by a possible dependence on magnetic local time or season, and the dependence on geomagnetic activity is weak and cannot be discerned. The performance of the model is evaluated by comparison to four previously developed empirical plasmaspheric models and a theoretical diffusive equilibrium model. The performance is further tested against the in situ passive IMAGE RPI measurements of the upper hybrid resonance frequency. While the equatorial densities of different empirical models are mostly within the statistical uncertainties, the clear latitudinal dependence of the RPI model presents an improvement over previous empirical models. This electron density model combined with a given model of the ion composition can be used to estimate the time for an Alfven wave to propagate from one hemisphere to the other, to determine the plasma frequencies along a field line, and to calculate the ray paths for high frequency waves propagating in the plasmasphere.