Simulation study on structure formation due to ion cyclotron instabilities

极光是由氧和氮分子的电离产生的，由于高速电子的碰撞，这些电子沿着电离层中的沿着磁场线加速。为了研究这些高速电子的产生机制，我们开发了自组的开边界二维半静电粒子模拟程序，并成功地证明了V形直流电势结构是由电流驱动的静电离子回旋不稳定性产生的。我们已经进行了几次模拟运行，以调查获得的电势差和潜在的结构依赖于系统的长度和当前层的宽度。结果发现，所获得的电位差随着模拟系统的增加而增加。这一结果表明，对于几千公里的异常电阻率长度，可以得到几千伏的电位差。这与极光加速一致。电势结构的宽度几乎等于电流层的宽度。此外，通过选择模拟参数，使得静电离子回旋波和离子声波都不稳定，进行了模拟运行。结果表明，在这种情况下，离子回旋波是占主导地位的。

Aurora is generated by ionization of oxygen and nitrogen molecules due to collision of high speed electrons which are accelerated along magnetic field lines in the ionosphere. In order to investigate the generation mechanism of these high speed electrons, we had developed self-consisted open-boundary two and a half dimensional electrostatic particle simulation code and had succeeded in demonstrating that the V-shaped dc potential structure is created by current-driven electrostatic ion-cyclotron instability. We have performed several simulation runs to investigate attained potential difference and potential structure dependencies on the system length and the width of the current layer. It is found that the attained potential difference increases with an increase in the simulation system. This result suggests that one can get several kV potential differences for several thousand-kilometer anomalous resistivity length. This is consistent with the auroral acceleration. The width of potential structure is almost equal to the width of the current layer. Furthermore, simulation runs have been performed by choosing simulation parameters such that both of electrostatic ion-cyclotron wave and ion acoustic wave are unstable. It has been shown that the ion cyclotron wave is dominant in this situation.