Leaked AKR and Terrestrial Hectometric Radiations Discovered by the Plasma Wave and Planetary Plasma Sounder Experiments on Board the Ohzora (EXOS-C) Satellite—Instrumentation and Observation Results of Plasma Wave Phenomena

Planetary plasma sounder (PPS) experiments system is installed in the Ohzora (EXOS-C) satellite which was launched on February 14, 1984, in an orbit with initial apogee and perigee of 865 km and initial perigee of 354 km, respectively, and initial inclination of 74.6°. Utilizing orthogonal 40 m (tip to tip) antennas and swept frequency receivers in the range from 100 kHz to 16 MHz and using a swept frequency VLF receiver in the range from 500 Hz to 20 kHz, PPS is operated for two main purposes. One operation is for the reception of natural plasma waves, both in the high frequency and the VLF ranges, and the other operation is for active experiments using the high power (300 W maximum) transmitter of the RF pulse where, in the normal mode, the swept frequency signal from 100 kHz to 16 MHz is modulated with a pulse width of 244 µsec. During the first three months after the deployment of the 40 m antennas which was made on May 16, 1984, data from more than 500 orbits have been obtained. From these data the following phenomena have been discovered: 1) Leaked component of auroral kilometric radiation, 2) Terrestrial hectometric radiation from the topside region of the ionosphere. In the frequency range from 100 kHz to 450 kHz, there exist emissions separated from LF Hiss; the cause of the emissions is attributed to leakage of the auroral kilometric radiation. The leaked components are believed to be produced by the conversion of Z-mode waves to whistler mode waves. With cooperative operation of the stimulated plasma wave experiments (SPW), it is shown that an enhancement of terrestrial hectometric radiation is related to irregularities of plasma density. This result also suggests that the conversion of Z-mode waves to L-O mode waves is taking place near the source regions.