Studies on acceleration processes of Iogenic gas and plasma based on stational observations at a suitable site for optical observations

本研究的主要目的如下：1）木星卫星木卫一的气体是如何产生并从木卫一释放出来的，它们被认为是木星磁层的主要等离子体源; 2）等离子体是如何加速到接近共转的速度的;以及3）如从地面观测和行星探测器所知，离子等离子体如何从气体刚产生后的冷态热化到热态。为了研究它们，每年大约有一个月在Mt.夏威夷毛伊岛的哈雷卡拉是世界上最好的光学观测站之一。并分别对这三个科学课题进行了数值模拟.观察结果：1）这是一个东西不对称的离子成因钠气体，它分布在几十个木星半径之外（钠星云）。2)木卫一轨道附近的等离子体速度总是 关于我们 s慢于共转速度，且速度具有磁经度依赖性和晨昏不对称性。3)在与木星磁场平行和垂直的方向上，得到了木卫一轨道附近的等离子体温度.数值模拟结果表明：（1）离子气体（钠星云）的主要释放过程是离子等离子体的解离或解离复合，当木卫一位于黎明/黄昏两侧时，释放的气体量最大/最小; 2)在木卫一轨道附近的等离子体和木星电离层之间形成一个电流回路，由于太阳紫外辐射的局部时间依赖性，该电流回路具有电导率的纵向不对称性，准均匀的纵向电流将使观测到的加速等离子体流动速度慢于黎明-黄昏不对称的共转速度。3)在刚电离的离子等离子体中，由于“环形分布”引起的等离子体不稳定性，会产生离子回旋波，这种波通过波粒相互作用（俯仰角散射）使等离子体热化，从而形成观测到的热条件。少

The main purposes of this study are the followings: 1) How the gases originated from Jupiter's satellite Io, which are considered to be main plasma source of Jupiter's magnetosphere, are generated and released from Io, 2) how the Iogenic plasma is accelerated to nearly corotation speed, and 3) how the Iogenic plasma is thermalized from the cold state just after the gas is generated to the hot state as known from ground based observations and planetary explorers. In order to investigate them, regular optical observations for the Iogenic gas and plasma had been carried out about one month a year at Mt. Haleakara, Maui, Hawaii which is one of the best optical observation sites in the world. And, numerical simulations had been made for the three scientific subjects, respectively.1. Results of the observations: 1) These is always an east-west asymmetry of the Iogenic sodium gas which is distributed beyond several tens Jovian radii (sodium nebula). 2) The plasma speed near Io's orbit is alwa … More ys slower than the corotation speed, and the speed shows magnetic longitude dependence and dawn-dusk asymmetry. 3) Plasma temperatures near Io's orbit is derived for the parallel and perpendicular directions with respect to Jupiter's local magnetic field.2. Results of the numerical simulations: 1) The dominant release process of the Iogenic gas (sodium nebula) would be dissociation or dissociative recombination of the Iogenic plasma, and the amount of the released gas would be largest/smallest when Io is in the dawn/dusk sides. 2) A current circuit would be made between the plasma near the Io orbit and Jupiter's ionosphere which has longitudinal asymmetry in the conductivity due to the local time dependence of the solar UV irradiation, and quasi-uniform longitudinal currents would make the observed accelerated plasma flow which is slower than the corotation speed with the dawn-dusk asymmetry. 3) Iion-cyclotron waves would be generated in the just ionized Iogenic plasma due to a plasma instability induced by the "ring distribution", and the waves might make the observed thermal conditions by thermalizing the plasma through the wave-particle interaction (pitch angel scattering). Less