Institute of Space and Aeronautical Science, University of Tokyo
Abstract
磁気圏衛星は,1978年9月16日成功裡に遠地点30056km,近地点227km,軌道傾斜角-31.1°で打ち上げられた.この軌道は,プラスマポーズを横切り,波動粒子相互作用を観測し解明するのに適した軌道である.現在,多くの成果が得られつつある.この衛星は,アナロク系のデータ伝送系をもっていて,10kHzから3MHzに至る広い周波数帯にわたって,450Hzから10kHzの帯域幅で波動現象をとらえることができる.本論文は,この波動現象に関連して,成果の全体を速報的にまとめたものである.現在,磁気圏衛星で観測されつつある重要な波動現象は,1)オーロラキロメートル波放射2)高域ハイブリットモード放射3)(n+1/2)f_c放射,(F_cは電子シャイロ周波数)4)ホイスラ,コーラスおよびヒスといった主要なVLF現象5)VLF領域の単純音(狭帯域)放射現象6)人工的に励起されたプラズマ波とその応用によるプラスマパラメーターの計測7)惑星電波8)タイプIII太陽電波ハーストである.波動粒子相互作用過程を解明する第一段階として,粒子のエネルギー分布も計測された.特に,UHRモードやELFおよびVLF帯放射との対応を求めることができた.また,500μsの幅のRFパルスにより,n=20までに至るサイクロトロン高調波や,125ms間も持続するUHR放射が観測されている.さらに今後,「じきけん」では,こうした観測を継続していくが,これに加え,南極のサイプルで発射されるVLF電波の受信および,EXOS-Aや外国のいわゆるIMS衛星(ISEE, GEOS)との共同観測も行い,磁気圏におけるオーロラ現象の原因を解明していく.JIKIKEN (EXOS-B) was successfully launched on September 16, 1978 into the orbit with initial apogee of 30056 km and perigee of 227 km, with inclination of -31.1°; the orbit is suitable for the investigation of the wave-particle interaction process in the plasmasphere and the magnetosphere near the plasma-pause. The analog data transmission system is used and fine structure of the dynamic spectrum in a swept frequency range from 10 kHz to 3 MHz has been obtained and wide band spectra from several 100 Hz to 10 kHz. The important wave phenomena obtained by current observation of JIKIKEN are. 1) Auroral (Earth) kilometric radio waves ; 2) Upper hybrid mode emissions ; 3) (n+l/2)f_c emission where f_c is the electron gyrofrequency ; 4) Principal phenomena of VLF frequency range, such as whistler, chorus, and hiss ; 5) Pure tone emissions (narrow band emission) in VLF range, 6) Artificially stimulated plasma waves and observation of plasma parameters ; 7) Planetary radio waves ; 8) Solar type III outburst. As a preliminary approach to verify the wave particle interaction processes, investigations of the energy spectra have also been made for the cases of the UHR mode plasma wave and the pure tone (narrow band) emission in ELF and VLF range. UHR resonance with long duration has been triggered by 500 μs pulse in the stimulated plasma wave experiment ; the resonance persists up to 125 ms,even in VLF range (below 30 kHz) ; and the electron cyclotron resonances are stimulated at very high harmonics number n, in the maximum case, sometimes n=20. The plasmapause electron density distributions are obtained from these resonance frequencies. The injection of an electron beam from the spacecraft stimulates electrostatic waves and also causes turbulent heating in the surrounding plasma. Bursts of energetic particles of keV energies are frequently encountered outside the plasma-pause Future programs of the EXOS-B experiment include the VLF signal obseivation transmitted from Siple Station, Antarctica, and coordinated observations with the EXOS-A and other IMS dedicated satellites to reveal the source and physical mechanism of auroral phenomena in the magnetospher
