Study of Plasma Turbulence by Means of Bispectrum Anaylyses

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The experimental study on the nonlinear wave-wave interactions in the space plasma was carried out by using both the ISIS-2 satellite observations of Siple Station VLF transmitter signals and the Aureol-3 satellite observations of Alpha VLF signals. We suceeded in analysing extremely a lot of data, and the results can be summarised as follows :(1)The analysis of Siple signals has indicated that we could detect the sideband structures on the ISIS-2 satellite, as was first observed by Tanaka, Hayakawa et al.(1987). Then the bispectrum analysis indicated that these sidebands are due to the nonlinear coupling between VLF transmitter signal and the pre-existing ELF emission in the ionosphere.The further analyzes of Aureol-3 satellite data of Alpha VLF transmission, has yielded some more evidence of the detection of sideband structures due to the monlinear interaction. The direction finding measurement has suggested that this interaction takes place between an electromagnetic strong VLF signal and a quasi-electrostatic ELF emission. The sideband wave is also found to be quasi-electrostatic, which can be confirmed by the fact that such sidebands are only detected on electric antennas.