Plasma electrons in Saturn's magnetotail: Structure, distribution and energisation
Plasma electrons in Saturn's magnetotail: Structure, distribution and energisation
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DOI：
10.1016/j.pss.2009.09.007
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发表时间：
2009-12-01
影响因子：
2.4
通讯作者：
Young, D. T.
中科院分区：
文献类型：
--
作者：
Arridge, C. S.;McAndrews, H. J.;Young, D. T.
本文利用 2006 年卡西尼号等离子体电子和磁场数据研究了土星的夜面和黎明前电子（0.5 eV-28 keV）等离子体片。提出了案例研究，举例说明了等离子体片的典型和非典型状态，并辅以等离子体片的统计研究。土星的夜面和黎明前的电子等离子体片存在两种状态：一种是静止状态，电子温度稳定在 100 eV 左右，其中电子分布函数最好用 Kappa 分布来表征；另一种是扰动状态，其中电子温度很高（类似于 1 keV），经常出现在暖层和热层之间的交替层中。还提供了双峰冷/暖（安静和干扰状态）和暖/热分布（干扰状态）的证据。这些扰动状态在质量上类似于地球磁尾在重新连接间隔期间的电子分布，我们认为这些扰动状态也是尾部重新连接周期造成的。我们提供了电子数密度、温度、部分电子β和压力的统计数据，并表明大的部分β值是必要的，但不足以唯一地识别中心等离子体片。最后研究了电子等离子体片的热力学性质，并表明电子的行为是等温的。这些结果对于建模和理论分析以及用于检查土星磁层动力学的研究非常重要。 (C) 2009 Elsevier Ltd. 保留所有权利。
In this paper Saturn's nightside and pre-dawn electron (0.5 eV-28 keV) plasma sheet is studied using Cassini plasma electron and magnetic field data from 2006. Case studies are presented which exemplify the typical and atypical states of the plasma sheet, and are complemented by a statistical study of the plasma sheet. It will be shown that Saturn's nightside and pre-dawn electron plasma sheet exists in two states: a quiescent state with a steady electron temperature of similar to 100 eV and where the electron distribution functions are best characterised by Kappa distributions, and a disturbed state where the electrons are hot (similar to 1 keV) and often seen in alternating layers between warm and hot populations. Evidence is also presented for bimodal cold/warm (both quiet and disturbed states) and warm/hot distributions (disturbed states). The disturbed states are qualitatively similar to electron distributions from Earth's magnetotail during intervals of reconnection and we argue that these disturbed states also result from periods of tail reconnection. We present statistics of electron number density, temperature, partial electron beta, and pressure, and show that large values of partial beta are necessary but not sufficient to uniquely identify the central plasma sheet. Finally the thermodynamic properties of the electron plasma sheet are studied and we show that the electrons behave isothermally. These results are important for modelling and theoretical analyses, and for use in studies which examine dynamics in Saturn's magnetosphere. (C) 2009 Elsevier Ltd. All rights reserved.