Terrestrial kilometric radiation observed by satellite JIKIKEN (EXOS-B).

Abstract

The natural plasma wave astronomy mode (NPW-A) on board JIKIKEN (EXOS-B) launched on Sept. 16, 1978, are making observation of the planetary and solar radio waves in the frequency range from 10kHz to 3MHz using the long dipole antenna with length of 102m. The high resolution spectrum obtained by the NPW-A receiver provides important characteristics of the terrestrial kilometric radiation (TKR) that carries the information on the source region where TKR is generated.When the source mechanism that the electrostatic waves near the upper hybrid frequency generated by auroral precipitating particle is converted in a form of the electromagnetic waves is considered, we can estimate the position of the TKR source from the measured spectrum. The height distribution of the source region derived from the frequency component of the radiation indicates the altitude range that varies in accordance with the geomagnetic activity, and ranging from 3, 000km to 12, 000km above the auroral ionosphere. The fine structure of TKR spectrum shows that the source with the dimension of 100km is moving down repeatedly toward the polar ionosphere with the average velocity of 5-10km/sec, and suggests that the source motion is closely related to the formation and the structure of the parallel electric field. The TKR emission sometimes coinsides with the intense upper hybrid emission around the satellite position at the inner edge of the dusk side plasmasheet, indicating that TKR has intimate relation to the energetic particle precipitation that generates the UHR waves; the precipitating particles may contribute to the development of the auroral field aligned currents.