Multisatellite determination of the relativistic electron phase space density at geosynchronous orbit: An integrated investigation during geomagnetic storm times

Abstract

An integrated investigation method, which can study the relativistic electron phase space density distribution and check the reliability of employed magnetic field models simultaneously, is developed and applied to the geosynchronous orbit region for 53 geomagnetic storms during a ∼190‐d period. First, to test how the magnetospheric magnetic field affects the study of phase space density, two approaches are taken on handling the magnetic field model: One is to use an existing empirical model through the whole storm period; the other is to select one from a list of existing magnetic field models for each time bin during the period by fitting to multipoint in situ measurements. The magnetic field models in both approaches are again tested by Liouville's theorem, which requires the conserved phase space density for fixed phase space coordinates given no local losses and sources. Then on the basis of the selected magnetic field model, the phase space density is calculated by transforming the flux data from three Los Alamos National Laboratory geosynchronous satellites. By following the procedure developed here and using the cross‐satellite calibration achieved in previous work, we deduce the storm time electron phase space density distribution for the region near geosynchronous orbit, covering a range of L shells with L* centered ∼6. This work establishes the radial phase space density gradient at constant adiabatic invariants as a function of universal time during storm times, and three types of geomagnetic storms are defined according to the degree of energy‐dependent enhancements of energetic electrons during recovery phases. Initial results from this study suggest a source outside geosynchronous orbit for low‐energy electrons and a major source inside for high‐energy electrons.