Study on Global Structure of Space Plasma Wave Energy by Using Large Scale Ray-Tracing

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The main objectives of this project were (1) to extend our ray tracing technique for calculating ray paths of VLF and ELF waves in the earth magnetosphere and (2) to apply this technique to the VLF and ELF waves observed by Akebono satellite for interpretation of these wave phenomena. Important results are summarized :1. The computer programs for ray tracing of VLF whistler mode and ELF ion cyclotron mode, both originally developed for supercomputers, were transplanted to workstations and completed various graphic routines to represent the results of calculation on a display and to get hardcopies on request.2. Application of the above ray tracing system to the wave data observed by the Akebono Satellite are as follows :a) By the VLF wave instruments on-board the satellite, Omega signals (10.2KHz) for ground navigation have been observed and spatial distributions of their signal intensity and wave normal direction in the magnetosphere were determined. These results can be compared with those theoretically calculated by ray tracing technique, if an appropriate Plasma model in the magnetosphere is given. We have developed a method to make a plasma density model which best fits the electron density actually observed along the satellite trajectory. It was found the results of ray tracing using the plasma model thusmade satisfactorily agree with those observed by Akebono.b) By the ELF wave instrument on-board the satellite, new ELF emission phenomena were discovered, which exist only in the magnetic equatorial region in the frequency range below 100Hz. These emissions are closely related with ion cyclotron frequency of Helium and Oxygen ions, so that they are interpreted as ion cyclotron mode emissions generated by an anisotropic temperature of super-thermal protons. In order to confirm this hypothesis, our ray tracing technique has been used and our interpretation was found to be satisfactory.