Generation and Evolution of Two Opposite Types of Mesoscale Plasma Sheet Bubbles
Generation and Evolution of Two Opposite Types of Mesoscale Plasma Sheet Bubbles
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DOI：
10.1029/2020ja028072
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发表时间：
2020-09
期刊：
影响因子：
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通讯作者：
Chih‐Ping Wang;Jian Yang;M. Gkioulidou;L. Lyons;R. Wolf
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文献类型：
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作者：
Chih‐Ping Wang;Jian Yang;M. Gkioulidou;L. Lyons;R. Wolf
以往的观测表明，中尺度等离子体片气泡(总熵相对低于环境等离子体的等离子体)主要有两种类型：类型1密度低于环境等离子体，温度高于环境等离子体，类型2具有相反的差异。我们首先从观测的统计分析中发现，第一类和第二类气泡都可能是通过磁尾中的磁重联局部产生的。然后，我们基于赖斯对流模型进行了模拟，表明气泡的密度和温度特性可以通过磁漂移和沉淀影响气泡的演化以及与之相关的磁场和流动扰动。对于这两种类型的气泡，气泡在向内移动时沿方位延伸，而BZ在气泡向地球的前沿附近得到加强。气泡内部的流动扰动由两个交换流涡组成，气泡中心附近有一条快速的向地面流动通道，气泡两侧有回流。气泡的低熵是由于第二类气泡中高能离子的减少，而第一类气泡中较低能离子的减少。气泡耗尽的高能离子向黄昏方向的磁漂移允许第二类气泡和BZ增强在黄昏时在方位上比第一类气泡扩展得更宽。与第一类气泡相比，第二类气泡中的电子产生较弱的电离层电导，特别是在气泡的黎明侧，因为这些电子向黎明漂移，这导致在黎明侧流动涡旋内的流动更强。
Previous observations showed that there are two major types of mesoscale plasma sheet bubbles (plasma with relatively lower total entropy than ambient plasma): the type‐1 has density lower and temperature higher than ambient plasma, and the type‐2 has the opposite differences. We first show, from statistical analysis of observations, that both the type‐1 and type‐2 bubbles can be possibly generated locally by magnetic reconnection in the magnetotail. We then conduct simulations based on the Rice Convection Model to show that the density and temperature characteristics of a bubble can affect the bubble's evolution and associated magnetic field and flow perturbations through magnetic drift and precipitation. For both types, the bubble extends azimuthally as it moves inward, and Bz is enhanced near the bubble's earthward front. The flow perturbations within the bubble consist of two interchange flow vortices with a fast earthward‐flow channel near the center and return flows on the two sides. The low entropy of a bubble is contributed by the reduction in the higher energy ions in the type‐2 bubble but in the lower energy ions in the type‐1 bubble. Duskward magnetic drift of the bubble's depleted high‐energy ions allows the type‐2 bubble and the Bz enhancement to expand azimuthally wider toward dusk than does the type‐1 bubble. The electrons within the type‐2 bubble produce weaker ionospheric conductance, in particular on the dawnside of the bubble because these electrons drift toward dawn, which results in stronger flows within the dawnside flow vortex, as compared to the type‐1 bubble.