transmission and of pause of the transmission. The shaded area shows the enhancement of the spectrum caused by the transmission of the 2.45 GHz microwave from the rocket. The local electron cyclotron frequency FH and its harmonics as well as the local electron plasma frequency is shown in the figure for reference. The biggest enhancement appears at a frequency in between the first and second harmonics of the electron cyclotron frequencies. It is inferred that this enhancement is due to the excitation of the electron cyclotron harmonic waves excited by the transmitted electromagnetic microwave. The reason for the inference is that this peak in the spectrum decreases in frequency with altitude showing a good correlation of the decreasing cyclotron frequency. A broad but less intense enhancement around 5 MHz-8 MHz showed a good correlation with the local electron plasma frequency and is inferred to be the electron plasma waves excited by the Raman scattering of the transmitted microwave. 3. MODEL AND CODE OF COMPUTER SIMULATION Electrostatic electron cyclotron harmonic waves are known to show the least damping when they propagate perpendicularly to the external magnetic field. The observed cyclotron waves may, therefore, well propagate in this direction because the necessary energy input from the microwave is minimum for this angle of propagation. Taking this fact into account, we hired a model in which all waves are assumed to propagate in the perpendicular direction relative to the external magnetic field. The exciting electromagnetic wave is assumed to be the O-mode wave for the present study. In other words, we examined a possibility of a nonlinear decay process of a high intensity O-mode electromagnetic wave into another electromagnetic wave and the electrostatic electron cyclotron wave. A schematic w-k diagram of this nonlinear decay process is depicted in Fig. 2. The simulation parameters are as follows:
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