of the transmitted microwave from the rocket was the same as that of the SPS microwave, the effective time of exposure of the microwave to the ionospheric plasma was too short compared with the characteristic time of the Ohmic heating because the rocket passes through the ionospheric plasma too quickly. As to the nonlinear excitation of the plasma waves, the result was clearly positive. The HF receiver showed a clear difference in the frequency spectra of the plasma waves when the microwave transmission was on and off. One example of the dynamic spectrum of the measured plasma wave for the period from 120 to 210 sec after launching is shown in Fig. 4. The second horizontal line from the top shows the on and off of the microwave transmission. The vertical axis is the frequency from 0.1 to 9 MHz. The horizontal axis show a time scale from 120 to 210 sec. The dark and light bar on the line indicate the timings of the transmission and pause, respectively. The horizontal line appearing at the frequency 3.1 MHz is an interference from the beating of the two frequencies used for the telemetry. Two different types of strong waves are seen excited only during the periods of the microwave transmission. One is the waves around 1.5 MHz and its harmonics. The frequency does not change much but shows only a slight decrease in time, i.e., with altitude. This wave turns out to be the electrostatic electron cyclotron harmonic waves judging from the comparison with the local electron cyclotron frequency. The second type of plasma waves excited by the microwave changes its frequency from 4 MHz to 6 MHz with altitude. The frequency of the wave turns out to be almost equal to the local electron plasma frequency. Thus this wave is supposed to be the electron plasma wave excited by the Raman scattering process of the transmitted microwave. The present MINIX revealed that the strong microwave energy beam is subject to nonlinear decay instabilities and causes the nonlinear excitation of electron cyclotron and plasma waves in the ionosphere.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==