Study on the Impulsive Plasma Wave Burst Phenomena Associated with Auroras

在Akebono(EXOS-D)卫星上成功地进行了等离子体波和探测仪实验，沿卫星轨道的初始近地点、远地点和倾角分别为300KN、10500 KM和68ﾟ；还在覆盖低到高海拔范围的极地电离层进行了观测。极区高空观测的目的是探索极光粒子的加速区，而低空极地电离层观测则是探测与极光形成和电离层扰动有关的能量耗散区。极光粒子与电离层等离子体和中性气体的强烈相互作用使极光热层在整个高度范围内处于扰动状态。本文主要研究在低…哨声模波频率范围内观测到的脉冲等离子体波爆发的发射利用Akebono卫星上的等离子体波电场探测天线和探测仪实验(PWS)，使2000公里以下的极地电离层更高。在1997至1998年的研究期间，对极地电离层中的波粒相互作用进行了理论研究，并对Akebono(EXOS-D)卫星的PWS数据进行了数据存储和分析。数据分析的结果表明，IPB的发射频繁地被观测到，表现为一组电场幅度在数百-几mV/m之间的强脉冲。利用自旋调制效应对两套偶极子天线探测到的电场进行了传播方向识别，结果表明IPB属于静电哨模式等离子体波，其波数向量与周围磁场有很大的传播角。辐射脉冲特征的起源可以归因于激发波的短暂性质的表现；即持续时间估计在20至200毫秒之间。用等离子体哨声波支的理论方法解释了IPB的这些主要特征，计算了与极区F区和电离层顶部低能电子束有关的束流等离子体不稳定性条件下静电哨声模波区的色散关系。IPB的短暂特性被认为是由于静电哨模式等离子体波进入非自由能空间时产生的严重的衰减效应所致。然后，IPB的观测区域被限制在靠近等离子体不稳定的区域，这可能是由与极光相关的低能电子引起的。虽然对脉冲产生低能电子的起源的探索被推迟到未来的研究中，但可以推断，极光粒子沉淀进入极地电离层会产生超热电子束，形成具有周期调制的连续群。较少

Plasma Waves and Sounder (PWS) Experiment on board the Akebono (EXOS-D) satellite has been successfully carried out through the entire regions along the satellite orbit with initial perigee, apogee and inclination of 300 kin, 10,500 km and 68ﾟ, respectively ; the observation have also been made in the polar ionosphere covering from low to high altitude ranges. The high altitude observation in the polar region is aimed to explore the acceleration region of auroral particles ; in the low altitude polar ionosphere, on the other hand, observations have been made for sounding the energy dissipation region related to formation of auroras and ionospheric disturbances. Strong interactions of the auroral particles with ionospheric plasma with neutral gases makes disturbed states in entire altitude range of the auroral thermosphere.The present research work has been focused on the emissions of impulsive plasma wave burst (IPB) observed in the frequency range of the whistler mode waves in the low … More altitude polar ionosphere below 2,000 km by using electric field detecting antenna of plasma waves and sounder experiment (PWS) on-board the Akebono satellite. Within the research period form 1997 to 1998, the research activities have been directed to the theoretical research of the wave particle interactions in the polar ionosphere as well as data archiving and analysis of PWS data from the Akebono (EXOS-D) satellite.The results of the data analysis shows that the emissions of IPB are frequently observed indicating a group of intense impulses with electric field amplitude of several hundreds muV/m to several mV/m. The propagation directions identified by using the spin modulation effect on the electric fields detected with the two sets of dipole antennas showed that IPB's belong to the electrostatic whistler mode plasma waves whose wave number vectors have a large propagation angle from the ambient magnetic field. The origin of impulsive signatures of emissions can be attributed to the manifestation of the short lived nature of excited waves ; namely, the duration time is estimated to be in the range from 20 to 200 msec. These major characteristics of IPB are consistently interpreted with the theorecal approach to the whistler mode branch of the plasma waves, calculating the dispersion relation in the regime of electrostatic whistler mode waves under the condition of beam plasma instability related to the low energy electron beam in the F-region and topside ionosphere of the polar region. The short lived feature of IPB is understood as being resulted by severe damping effects of the electrostatic whistler mode plasma waves when the waves enter into the space of non free energy. The observation region of IPB is then limited in the region close to plasma instability that is possibly caused by the low energy electrons associated with auroras. Though the quest for origin of the impulsive generation of low energy electrons is deferred for future studies, it is inferred that the auroral particle precipitation into the polar ionosphere generates suprathermal electron beams forming successive groups with periodic modulation. Less