PLASMA WAVE OBSERVATION AND STIMULATION EXPERIMENTS (PWS) USING THE (EXOS-D) SATELLITE : Instrumentation and initial results including discovery of the high altitude equatorial plasma turbulence
The Plasma waves and sounder experiment (PWS) onboard the Akebono (EXOS-D) satellite have been successfully conducted after the deployment of the antenna and the turning on the instruments on March 4,1989. In natural plasma wave observations, the dynamic spectra of the plasma waves in a whole range of the orbits are observed in the PWS frequency range from 20kHz to 5MHz. The results are summarized as follows. i) The upper hybrid emissions that cover from the electron cyclotron frequency f_C to the upper hybrid frequency f_<UHR> for the case where f_C are higher than the local plasma frequency f_P, or cover from f_P to f_<UHR> for the case of f_P>f_C, are observed throughout whole path ranges of the satellite. From the global distribution of the upper hybrid frequency emissions, the structures of the plasmasphere are clarified. ii) Auroral kilometric radiations are observed in the region associated with the auroral particle acceleration regions. The Polarization and Poynting vectors of AKR are also precisely measured. The data show the possibility for studies of the structure of the acceleration regions in addition to the generation mechanism of AKR. The AKR data that have been obtained in the acceleration region of the auroral particles are especially important suggesting the possible co-existence of the electrostatic plasma waves with the Z-mode waves. iii) In the equatorial region of the plasmasphere the enhancement of the upper hybrid mode waves have been discovered; the enhancement shows two possible plasma turbulences, the first is the enhancement of the microscopic instabilities that are indentified only as the enhancements of the intensity of the upper hybrid emissions and called "equatorial enhancement of the wave turbulence (EPWAT)"; the second is the enhancement of the irregular change of the upper hybrid frequency suggesting the turbulent variation of the plasma density called "equatorial enhancement of the density turbulence (EPDET)". EPWAT's are encircling the magnetic equator forming a disc within altitude range of 1000km to 9000km, while EPDET's encircle the geographic equator within altitude range of 1000km to 9000km forming another disc. iv) Sounder experiments of the PWS have also been carried out; the results show the principal resonances such as plasma resonances at f_P, upper hybrid resonances at f_<UHR>, and harmonics of the electron cycoltron frequency at nf_C (n=1,2,3,...). The sequence of diffuse plasma resonances f_<Dn> with the static plasma wave resonance f_<Qn> are also detected even in a high altitude range higher than 3000km. Very long ducted echoes of the sounder transmitting pulses have also been detected even at an altitude of 6000km. All these results of the experiments reveal that the PWS/EXOS-D data are proving very promising key for the studies of the plasma and plasma weves through out the global ionosphere and plasmasphere, including the regions of auroral particle acceleration.
プラズマ波動及び波動励起観測実験 (PWS) による宇宙プラズマ波動観測 : あけぼの (EXOS-D) における PWS 観測装置と初期観測結果
SA0166922.pdf
(1.89MB)
