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首页> 外文期刊>Journal of Geophysical Research, A. Space Physics: JGR >Electron Cooling and Isotropization during Magnetotail Current Sheet Thinning: Implications for Parallel Electric Fields
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Electron Cooling and Isotropization during Magnetotail Current Sheet Thinning: Implications for Parallel Electric Fields

机译：电子冷却和Isotropization期间磁尾电流片变薄:影响对平行电场

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Magnetotail current sheet thinning is a distinctive feature of substorm growth phase, during which magnetic energy is stored in the magnetospheric lobes. Investigation of charged particle dynamics in such thinning current sheets is believed to be important for understanding the substorm energy storage and the current sheet destabilization responsible for substorm expansion phase onset. We use Time History of Events and Macroscale Interactions during Substorms (THEMIS) B and C observations in 2008 and 2009 at ~18-25 R_E to show that during magnetotail current sheet thinning, the electron temperature decreases (cooling), and the parallel temperature decreases faster than the perpendicular temperature,leading to a decrease of the initially strong electron temperature anisotropy (isotropization). This isotropization cannot be explained by pure adiabatic cooling or by pitch angle scattering. We use test particle simulations to explore the mechanism responsible for the cooling and isotropization. We find that during the thinning, a fast decrease of a parallel electric field (directed toward the Earth) can speed up the electron parallel cooling,causing it to exceed the rate of perpendicular cooling, and thus lead to isotropization, consistent with observation. If the parallel electric field is too small or does not change fast enough, the electron parallel cooling is slower than the perpendicular cooling, so the parallel electron anisotropy grows, contrary to observation. The same isotropization can also be accomplished by an increasing parallel electric field directed toward the equatorial plane. Our study reveals the existence of a large-scale parallel electric field, which plays an important role in magnetotail particle dynamics during the current sheet thinning process.
机译：磁尾电流片变薄亚暴增长阶段的独特的特性,在此期间存储在磁能量磁性层的叶。质点动力学在这种稀释当前表被认为是重要的理解亚暴能量储存和当前表不稳定负责亚暴扩张阶段开始。在事件和大规模交互亚暴(裁判)2008年B和C的观察和2009年在~ R_E表明,年龄在18岁至25岁之间磁尾电流片变薄,电子温度降低(冷却),平行温度下降速度比垂直温度,导致减少最初的强烈的电子温度各向异性(isotropization)。不能用纯绝热冷却或解释螺旋角散射。负责模拟探讨机制冷却和isotropization。在变薄,快速减少的平行的电场(指向地球)可以加快电子平行冷却,使其超过的速度垂直的冷却,从而导致isotropization,与观测一致。平行电场太小还是变化的速度不够快,电子平行冷却比垂直冷却慢,所以并行电子各向异性生长,与观察。也可以通过增加平行电场指向赤道平面。的大规模平行电场在磁尾粒子中扮演一个重要的角色动态电流片变薄的过程。

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