Determining Plasmaspheric Densities from Observations of Plasmaspheric Hiss

Abstract

AbstractA new method of inferring electron plasma densities inside of the plasmasphere is presented. Utilizing observations of the electric and magnetic field wave power associated with plasmaspheric hiss, coupled with the cold plasma dispersion relation, permits calculation of the plasma density. This methodology yields a density estimate for each frequency channel and time interval where plasmaspheric hiss is observed and is shown to yield results that are generally in agreement with densities determined via other methods. A statistical calibration is performed against the density from the upper hybrid line, accounting for both systematic offsets and distribution scatter in the hiss‐inferred densities. This calculation and calibration methodology provides accurate density estimates, both statistically and for individual events. These calibrated calculated densities are not subject to the same upper limit as densities inferred via other methodologies, thus permitting density estimates to be extended to lower L shells. This is of particular interest given that fpe/fce ratios indicate favorable conditions for efficient pitch‐angle and energy diffusion in this region. Since hiss is almost always observable inside of the plasmasphere, the hiss‐inferred densities are available for the majority of time periods, with 79% data coverage for L < 4. This compares to 33–37% data coverage for other methods of inferring plasma densities. Due to the high‐accuracy of these hiss‐inferred densities and their plentiful availability, this methodology provides a viable alternative of calculating event‐specific densities, and therefore diffusion coefficients, as opposed to relying on empirical models for periods when densities from other sources are not available.