Y. Goto

Determination of plasmaspheric electron density profile by a stochastic approach

[1]xa0The determination of plasmaspheric electron density profiles has been attempted using a stochastic approach, using Omega signals observed on the Akebono satellite. Since the wave normal directions and delay times of Omega signals can be theoretically calculated by ray tracing under an appropriate electron density model, the density profile can be estimated by fitting the calculated directions and times to the observed values. In the present paper, we introduce a flexible model and a novel algorithm in the fitting method, taking into account the stochastic factors of the density distribution and wave propagation. The stochastic representations of directions and times enable us to separately estimate the effects of the ionosphere and the plasmasphere. The validity of the proposed method is examined using observational data collected during the recovery phase of a magnetic storm. In another example, an estimation of the asymmetry of the plasmasphere is attempted.

A Flexible Modeling of Global Plasma Profile Deduced from Wave Data

As the plasma profile around the earth varies with local time, season and solar activity, it is important to have a means to determine it in a fine time resolution. In this paper we propose a method to determine the global plasma profile from the satellite observation data. We adopt a stochastic model to represent the distribution of plasma. In the model, the parameters are determined by ABIC(Akaike Bayesian Information Criterion) deduced from observed wave data. The validity of our method was evaluated using simulated data and it is found that the given distributions are successfully reconstructed by smoothing the observation data appropriately.

Direction Finding of the Waves in Plasma Using Energy Function

Investigation of space environment around the earth has become a critical issue. In addition to the artificial waves propagating from the ground, a variety of natural plasma waves generated in the magnetosphere are detected by scientific satellites. As the characteristics of these waves reect the plasma environment around the earth, it is important to measure the propagation (wave normal) directions of these waves. Since signals observed by a satellite may be a mixture of the waves from multiple directions, we must assume unknown parameters of these waves without prior information. In the present study, we propose a new direction finding method derived from the concept of energy function.