Global electron density distribution in the plasmasphere deduced from Akebono wave data and the IRI model

Abstract

Abstract Determination of global electron density distribution in the plasmasphere has been attempted using the wave normal directions and delay time of Omega signals, and in-situ electron density observed on the Akebono satellite. The present study is based on the assumption that the plasma model is represented by a diffusive equilibrium (DE) model with temperature gradient along a magnetic field line, and that the electron density at a reference altitude (1000km) is dependent on L-value. Relative concentrations of ion constituents H+, He+, and O+ at the reference altitude are determined by fitting as either L-independent or L-dependent. For the altitude range below the reference altitude, we have adopted a distribution which has one maximum density at the F2 peak and one minimum density at the E valley, both being referred to the IRI model. The parameters related to these models are determined by the non-linear least squares fitting method for the in-situ electron density, the wave normal direction and the delay time of Omega signals observed by Akebono. Wave normal directions and delay time at Akebono for the model are determined by ray tracing. The validity of our plasmaspheric model based on the DE model was checked by comparing it with the SUPIM (Sheffield University Plasmaspheric and Ionospheric Model), and we can conclude that our model is flexible enough to represent the general global distributions of the electron density in the plasmasphere, although it is possible that in some cases, unrealistic distributions of the plasma temperatures should be used in the model. The reliability of our fitting algorithm was also checked by computer simulations, and we have confirmed that the global electron density distribution can be determined from the satellite wave data, without any significant error. Several plasmaspheric electron density distributions are shown as a result of applying our method to Akebono data.