Study on nonlinear wave dynamics in the magnetosphere via computer experiments and plasma waveform analysis

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We have studied the nonlinear wave dynamics observed in the Earth's magnetosphere by using plasma waveform data obtained with the GEOTAIL spacecraft and by performing computer experiments with particle model. The analysis of waveforms enables us to extract the spatial as well as temporal nonlinear variation involved in each phenomenon. In particular, waveform analysis of electron modes observed at boundary layers such as the magnetic reconnection region is important in association of plasma heating, acceleration, and perturbation. The aim of this research project is to solve these microscopic nonlinear wave dynamics by performing computer experiments as well as analyzing the waveform data of GEOTAIL. We also utilized unique method in the statistical study of waveforms such as the pattern recognition as well as the conventional Fourier transformation. We paid our attention to the waveforms of broadband electrostatic noise (BEN), narrow band electrostatic noise (NEN), electron cyclotron … More harmonic waves (ECH), and amplitude modulated Langmuir waves. By combining the analysis of these waveform and computer experiments, we examined microscopic nonlinear processes in the wave dynamics.In particular, the discovery of the generation mechanism of BEN is very significant in the present research project. We, for the first time, found that BEN is made of electrostatic solitary waves (ESW) which are created by the beam-plasma interaction. By Performing computer experiments, we also revealed that ESW is a nonlinear solution of BGK mode generated by the beam-plasma instability. To statistically analyze ESW, we developed a new method using the bit-patter matching, and succeeded in extracting ESW waveforms automatically. We could clarify the relation between the propagation of ESW and that of electron beams, and the width of ESW and the local Debye length. The statistical analysis shows a good agreement with the results obtained in the computer experiments conducted in the present studies. Less