Multipoint Conjugate Observations of Dayside ULF Waves During an Extended Period of Radial IMF
Multipoint Conjugate Observations of Dayside ULF Waves During an Extended Period of Radial IMF
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DOI：
10.1029/2020ja028364
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发表时间：
2020-03
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通讯作者：
Xueling Shi;M. Hartinger;J. Baker;J. Ruohoniemi;D. Lin;Zhonghua Xu;S. Coyle;B. Kunduri;L. Ki
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文献类型：
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作者：
Xueling Shi;M. Hartinger;J. Baker;J. Ruohoniemi;D. Lin;Zhonghua Xu;S. Coyle;B. Kunduri;L. Ki
共轭地面磁力仪观测到了长持续的Pc 5超低频（ULF）波，这些波跨越了向阳面，并从L_25.5延伸到极冠区。MMS卫星对磁层的观测和地面磁强计的观测证实，闭合磁力线上的超低频波是由基本环形阿尔文驻波引起的。低纬度地区的单色波在上午和下午都倾向于在远离中午的地方最大化它们的功率，而高纬度地区的宽带波在中午附近往往有波功率最大值。在磁层顶穿越期间的波功率分布和MMS卫星观测表明，Kelvin-Helmholtz（KH）不稳定磁层顶上的表面波与Alfvén驻波耦合。更动荡的离子前震在径向行星际磁场（IMF）的一个延长的时期可能起着重要的作用，在提供种子扰动的增长KH波。这些结果表明，在极盖闭合场线和开放场线上观测到的Pc 5波来自同一个源。
Long‐lasting Pc5 ultralow frequency (ULF) waves spanning the dayside and extending from L ∼ 5.5 into the polar cap region were observed by conjugate ground magnetometers. Observations from MMS satellites in the magnetosphere and magnetometers on the ground confirmed that the ULF waves on closed field lines were due to fundamental toroidal standing Alfvén waves. Monochromatic waves at lower latitudes tended to maximize their power away from noon in both the morning and afternoon sectors, while more broadband waves at higher latitudes tended to have a wave power maximum near noon. The wave power distribution and MMS satellite observations during the magnetopause crossing indicate surface waves on a Kelvin‐Helmholtz (KH) unstable magnetopause coupled with standing Alfvén waves. The more turbulent ion foreshock during an extended period of radial interplanetary magnetic field (IMF) likely plays an important role in providing seed perturbations for the growth of the KH waves. These results indicate that the Pc5 waves observed on closed field lines and on the open field lines of the polar cap were from the same source.