土星磁层等离子体径向输运的数值模拟

本文建立了一个包含离心力效应的自洽稳态土星磁层模型，并且用等离子体细丝模型对土星磁层等离子体径向输运进行了数值模拟.模拟结果表明，Dione（土卫四）附近的等离子体可能因为发生离心交换不稳定性（Centrifugal Interchange Instability）而被输运到离土星更远的地方.这种输运现象的发生是由离心力主导的，等离子体的黏滞效应和能量转移对输运过程的影响非常小（几乎可以忽略不计），但土星电离层电导率对输运过程有重要影响，电导率越低，径向输运过程越快，反之，高电导率在一定程度上会阻碍输运的进行.在土星电离层电导率σ=2 S时，Dione（距离土星6.3R_S, R_S为土星半径）附近的等离子体在5.52个小时中被输运到距离土星10R_S的地方.本文的模拟结果还表明，密度受到扰动的等离子体是不稳定的，如果洛仑兹力和等离子体热压强梯度不能与离心力平衡，径向输运就会发生.密度大的等离子体在向外输运过程中会绝热膨胀而温度降低，密度小的等离子体则在注入磁层过程中因为绝热压缩而温度升高.

Numerical simulation of radial plasma transport in the saturn's magnetosphere

This paper constructs a self-consistent stationary model of the Saturn's magnetosphere,in which the centrifugal force is included.Based on the thin-filament model,numerical simulation of radial plasma transport in the Saturn's magnetosphere is carried out.The results show that the plasma near Dione may be transported to the farther place because of the centrifugal interchange instability.This type of transportation is dominated by the centrifugal force,the viscidity and energy transfer do little on the transportation(almost negligible)but the ionospheric conductance has important influence.Lower value of conductance causes faster transportation while higher value of conductance will block transportation to some extent.The plasma near Dione(6.3RS from the Saturn)has been transported to 10RS from the Saturn in 5.52 hours when the ionospheric conductance is set to 2 S.Our simulations also show that the plasma is unstable if the density is disturbed,when the Lorentz force and the gradient of plasma thermal pressure can not balance with the centrifugal force,radial transportation will happen.The radial plasma transport in the Saturn's magnetosphere is that the denser plasma becomes cooler because of adiabatic expansion in the process of outward transport while the injected lighter plasma becomes hotter due to the adiabatic compression.