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首页> 外文期刊>Journal of Geophysical Research, A. Space Physics: JGR >Dependence of Thermodynamic Processes on Upstream Interplanetary Magnetic Field Conditions for Magnetosheath Ions
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Dependence of Thermodynamic Processes on Upstream Interplanetary Magnetic Field Conditions for Magnetosheath Ions

机译：依赖上游的热力学过程行星际磁场条件磁鞘离子

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摘要

Using Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations over a 10-year period from 2008 to 2017, we statistically investigate the thermodynamic properties for magnetosheath ions and their dependence on upstream interplanetary magnetic field (IMF) conditions. The thermodynamic properties for magnetosheath ions are estimated by using the polytropic index averaged over the subinterval that belongs to the same streamline (α). The THEMIS observations show that the probability distribution of α for magnetosheath ions has a major peak at α~1 (quasi-isothermal conditions) with a longer left tail down to α~0 (quasi-isobaric conditions). The spatial distributions of α for two different types according to IMF spiral angle (i.e., Parker spiral and ortho-Parker spiral IMF orientations) reveal that the ions in the downstream of a quasi-perpendicular shock (quasi-perpendicular magnetosheath) exhibit quasi-isothermal processes, while those in the downstream of a quasi-parallel shock (quasi-parallel magnetosheath) show α lower than unity (down to α ~0.8) implying the anticorrelation between the ion temperature and the ion number density variations. Moreover, α in the quasi-parallel magnetosheath tends to decrease with increasing magnetic local time distance from the magnetic local noon. These results indicate that the thermodynamic properties for magnetosheath ions depend on the bow shock geometry (quasi-perpendicular bow shocks versus quasi-parallel bow shocks) and are presumably controlled by a variety of instabilities, waves, and turbulence in the magnetosheath.
机译：使用时间的历史事件和宏观尺度互动,在亚暴(裁判)从2008年到十年为一个周期的观察2017年,我们统计调查磁鞘离子的热力学性质和他们的依赖上游星际磁场(IMF)的条件。磁鞘离子的热力学性质估计使用多变指数吗平均的子区间属于相同的简化(α)。α的概率分布磁鞘离子有一个很大的峰值在α~ 1(quasi-isothermal条件)再离开尾巴α~ 0 (quasi-isobaric条件)。空间分布的两种不同的α类型根据国际货币基金组织(IMF)螺旋角(例如,帕克螺旋和IMF ortho-Parker螺旋方向)表明,离子的下游quasi-perpendicular冲击(quasi-perpendicular磁鞘)展览quasi-isothermal过程,而下游的quasi-parallel冲击(quasi-parallel磁鞘)α低于团结秀(α~ 0.8)之间的anticorrelation暗示离子温度和离子数密度变化。磁鞘倾向于减少而增加当地时间磁磁的距离当地的中午。磁鞘离子的热力学性质依赖于弓形激波的几何形状(quasi-perpendicular弓形激波与quasi-parallel弓形激波)和可能由各种不稳定,控制波,磁鞘和动荡。

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