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

这项研究的主要目的如下：1)木星卫星Io的气体是如何产生和释放的，Io被认为是木星磁层的主要等离子来源，2)Igenate等离子体如何加速到接近大转的速度，以及3)Igenate等离子体如何从气体产生后的冷态热化到从地面观测和行星探测器所知的热态。为了研究它们，每年大约有一个月在山上对同源气体和等离子体进行定期光学观测。夏威夷毛伊岛的哈雷卡拉是世界上最好的光学观测点之一。并分别对这三个科学课题进行了数值模拟。观测结果：1)这始终是一种东西不对称的同源钠气体，其分布超过几十个木星半径(钠星云)。2)Io轨道附近的等离子体速度为alwa…比自转速度慢的多，速度表现为磁经相关性和黎明-黄昏不对称性。3)求出了木星轨道附近相对于木星局部磁场的平行和垂直方向的等离子体温度。数值模拟结果表明：1)同源气体(钠星云)的释放过程主要是同源等离子体的解离或解离复合过程，当Io处于黎明/黄昏边时，释放量最大/最小。2)由于太阳紫外线辐射的局地时间依赖性，木星电离层与Io轨道附近的等离子体之间会形成一条电流回路，而准均匀的纵向电流会使观测到的等离子体加速流动慢于自转速度，具有黎明-黄昏的不对称性。3)由于“环分布”引起的等离子体不稳定性，在刚刚电离的同源等离子体中会产生离子-回旋波，这些波可能通过波-粒子相互作用(俯仰角散射)对等离子体进行热化，从而形成观测到的热条件。较少

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