Kelvin-Helmholtz Instability Associated With Reconnection and Ultra Low Frequency Waves at the Ground: A Case Study
Kelvin-Helmholtz Instability Associated With Reconnection and Ultra Low Frequency Waves at the Ground: A Case Study
复制标题
DOI：
10.3389/fphy.2021.738988
复制
发表时间：
2021-12
期刊：
影响因子：
--
通讯作者：
E. Kronberg;J. Gorman;K. Nykyri;A. G. Smirnov;J. Gjerloev;E. Grigorenko;L. Kozak;X. Ma;K. Trattner;M. Friel
中科院分区：
文献类型：
--
作者：
E. Kronberg;J. Gorman;K. Nykyri;A. G. Smirnov;J. Gjerloev;E. Grigorenko;L. Kozak;X. Ma;K. Trattner;M. Friel
开尔文-亥姆霍兹不稳定性（KHI）及其与太阳风到磁层的能量和质量转移相关的影响仍然是磁层物理学的重要焦点。其中一种效应是产生 Pc4-Pc5 超低频 (ULF) 波（周期为 45-600 秒）。 2007 年 7 月 3 日，磁当地时间 0500 时，星团空间任务在高纬度磁层顶遇到了 Pc4 频率的开尔文-亥姆霍兹波 (KHW)，并具有持续涡旋的特征。这些特征包括与总压增加相关的磁场法向分量的双极波动和涡流边缘密度的快速变化；磁鞘和磁层等离子体群的振荡；存在快速移动、低密度、混合等离子体；边界法线的准周期振荡以及边界速度的法线分量和平行分量之间的反相关系。根据 OMNI 数据和 THEMIS 在太阳下点的观测，该事件发生在行星际磁场南向时期。几个 KHI 涡旋与 Walén 关系所示的重联、德霍夫曼-特勒框架的存在、观察到的场对准离子束以及正常磁场分量中的双极波动以及新月形离子分布有关。该事件的全球磁流体动力学模拟也导致了磁层顶的 KHW。观测到的与重新连接相关的 KHW 与地面记录的 ULF 波一致，其特性表明它们是由这些波驱动的。这些属性包括 Cluster 磁足点的位置、Pc4 频率和太阳风条件。
The Kelvin-Helmholtz instability (KHI) and its effects relating to the transfer of energy and mass from the solar wind into the magnetosphere remain an important focus of magnetospheric physics. One such effect is the generation of Pc4-Pc5 ultra low frequency (ULF) waves (periods of 45–600 s). On July 3, 2007 at ∼ 0500 magnetic local time the Cluster space mission encountered Pc4 frequency Kelvin-Helmholtz waves (KHWs) at the high latitude magnetopause with signatures of persistent vortices. Such signatures included bipolar fluctuations of the magnetic field normal component associated with a total pressure increase and rapid change in density at vortex edges; oscillations of magnetosheath and magnetospheric plasma populations; existence of fast-moving, low-density, mixed plasma; quasi-periodic oscillations of the boundary normal and an anti-phase relation between the normal and parallel components of the boundary velocity. The event occurred during a period of southward polarity of the interplanetary magnetic field according to the OMNI data and THEMIS observations at the subsolar point. Several of the KHI vortices were associated with reconnection indicated by the Walén relation, the presence of deHoffman-Teller frames, field-aligned ion beams observed together with bipolar fluctuations in the normal magnetic field component, and crescent ion distributions. Global magnetohydrodynamic simulation of the event also resulted in KHWs at the magnetopause. The observed KHWs associated with reconnection coincided with recorded ULF waves at the ground whose properties suggest that they were driven by those waves. Such properties were the location of Cluster’s magnetic foot point, the Pc4 frequency, and the solar wind conditions.