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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Three-dimensional plasma simulation of Io's interaction with the Io plasma torus: Asymmetric plasma flow
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Three-dimensional plasma simulation of Io's interaction with the Io plasma torus: Asymmetric plasma flow

机译：Io与Io等离子体环面相互作用的三维等离子体模拟：不对称等离子体流

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A three-dimensional, stationary, two-fluid plasma model for electrons and one ion species was developed to understand the local interaction of Io's atmosphere with the Io plasma torus and the formation of Io's ionosphere. Our model calculates, self-consistently, the plasma density, the velocity and the temperatures of the ions and electrons, and the electric field for a given neutral atmosphere and imposed Io plasma torus conditions but assumes for the magnetic field the constant homogeneous Jovian field. With only photoionization in a pure SO_2 atmosphere it is impossible to correctly model the plasma measurements by the Galileo spacecraft. With collisional ionization and photoionization the observations can be successfully modeled when the neutral atmospheric column density is N_(col) = 6 * 10~(20) m~(-2) and the atmospheric scale height is H = 100 km. The energy reservoir of the Io plasma torus provides via electron heat conduction the necessary thermal energy for the maintenance of the collisional ionization process and thus the formation of Io's ionosphere. Anisotropic conductivity is shown numerically as well as analytically to be essential to understand the convection patterns and current systems across Io. The electric field is very greatly reduced, because the ionospheric conductances far exceed the Alfven conductance #SIGMA#_A, and also strongly twisted owing to the Hall effect. We find that the electric field is twisted by an analytic angle tan #THETA#_(twist) = #SIGMA#_2/(#SIGMA#_1 + 2#SIGMA#_A) from the anti-Jupiter direction toward the direction of corotation for constant values of the Pedersen and Hall conductances #SIGMA#_1 and #SIGMA#_2 within a circle encompassing Io's ionosphere. Because the electron velocity is approximately equal to the E * B drift velocity, the electron flow trajectories are twisted by the same angle toward Jupiter, with E and B the electric and magnetic fields, respectively. Since #SIGMA#_1 approx #SIGMA#_2, the electron flow is strongly asymmetric during convection across Io, and the magnitude of this effect is directly due to the Hall conductivity. In contrast, the ions are diverted slightly away from Jupiter when passing Io. Large electric currents flow in Io's ionosphere owing to these substantially different flow patterns for electrons and ions, and our calculations predict that a total electric current of 5 million A was carried in each Alfven wing during the Galileo flyby. We also find a total Joule heating rate dissipated in Io's ionosphere of P = 4.2 * 10~(11) W.
机译：建立了用于电子和一个离子物种的三维固定两流体等离子体模型，以了解Io大气与Io等离子体圆环的局部相互作用以及Io电离层的形成。我们的模型可以自洽地计算给定中性气氛和施加的Io等离子体圆环条件下的等离子体密度，离子和电子的速度和温度以及电场，但对于磁场假设恒定的均匀Jovian场。仅在纯SO_2气氛中进行光电离，就不可能正确地对伽利略号航天器进行的等离子体测量建模。通过碰撞电离和光电离，当中性大气柱密度为N_（col）= 6 * 10〜（20）m〜（-2）且大气标高为H = 100 km时，可以成功地建立观测模型。 Io等离子体环的储能器通过电子热传导提供必要的热能，以维持碰撞电离过程，从而形成Io的电离层。数值和分析方法都表明各向异性电导率对于理解Io上的对流模式和电流系统至关重要。由于电离层电导远远超过Alfven电导＃SIGMA＃_A，并且由于霍尔效应而强烈扭曲，因此电场大大减小了。我们发现电场从反木星方向朝着同心旋转方向扭转了解析角tan #THETA #_（twist）=＃SIGMA＃_2 /（＃SIGMA＃_1 + 2＃SIGMA＃_A）围绕艾奥电离层的圆圈内的Pedersen和Hall电导＃SIGMA＃_1和＃SIGMA＃_2的常数。因为电子速度大约等于E * B漂移速度，所以电子流动轨迹以相同的角度向木星扭曲，其中E和B分别是电场和磁场。由于＃SIGMA＃_1约为＃SIGMA＃_2，因此在跨Io的对流过程中，电子流非常不对称，这种效应的大小直接归因于霍尔电导率。相反，当通过Io时，离子会稍微偏离木星。由于电子和离子的这些明显不同的流动方式，大电流在艾奥电离层中流动，并且我们的计算预测，在伽利略飞越期间，每个阿尔夫芬机翼中将携带500万安培的总电流。我们还发现Io电离层的总焦耳加热速率为P = 4.2 * 10〜（11）W.

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