Global Plasmaspheric Imaging with a Flexible Model Deduced from the Plasma Waves Observed by the Akebono Satellite

Details Global Plasmaspheric Imaging with a Flexible Model Deduced from the Plasma Waves Observed by the Akebono Satellite Global Plasmaspheric Imaging with a Flexible Model Deduced from the Plasma Waves Observed by the Akebono Satellite

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm11a0778g&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #SM11A-0778

Physics

2768 Plasmasphere, 6982 Tomography And Imaging, 6984 Waves In Plasma

Scientific paper

As global plasma (electron) density profile in the Earth's plasmasphere varies with local time, season and solar activity, it is very important to determine it with a fine time resolution. Direct spacecraft observations are thought to be one of the most effective way to obtain the density accurately. It must be noted, however, that they can provide plasma parameters only along their trajectories. In order to get the global density profile with a fine time resolution, it is necessary to assume an adequate model of the density distribution. It is generally accepted that the most appropriate way to represent the plasma profile along geomagnetic field lines is a diffusive equilibrium density profile with a fixed temperature gradient in the plasmasphere. As for the vertical structure to the magnetic field lines, a parametric model was conventionally used, in which the degree of freedom, however, is limited and all the residual errors to the model are considered to be observational noises. In the present study, we propose a new flexible model in which stochastic fluctuation of the electron density profile is taken into account. To determine unknown parameters in the model, we use Omega signals around 10kHz, which had been used for global navigation and were continuously observed by the Akebono satellite. Using ray tracing technique, we determine the best plasma profile which satisfies these wave observation data, that is, wave normal directions and delay times, by giving the adequate parameters in our plasma model. The proposed method was evaluated using simulated data. It is found that local fluctuations along the trajectories were successfully removed and the global density distribution was reconstructed by smoothing the observational data appropriately. The proposed method was also applied to the observational data of the Akebono satellite. In the presentation, we introduce examples of global electron density profile in the disturbed plasmasphere. Acknowledgements: We thank H. Oya for providing the electron density data observed by Akebono. We also thank the Akebono/VLF members for their contribution to the VLF instrument and its data analyses.

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