How a Realistic Magnetosphere Alters the Polarizations of Surface, Fast Magnetosonic, and Alfvén Waves.
How a Realistic Magnetosphere Alters the Polarizations of Surface, Fast Magnetosonic, and Alfvén Waves.
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DOI：
10.1029/2021ja030032
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发表时间：
2022-03
影响因子：
2.8
通讯作者：
Wright, A. N.
中科院分区：
文献类型：
--
作者：
Archer, M. O.;Southwood, D. J.;Hartinger, M. D.;Rastaetter, L.;Wright, A. N.
地球磁层内系统尺度的磁流体(MHD)波通常是用盒子模型从理论上理解的。虽然这些方法对理解目前各种波动模式的许多基本特征非常有指导意义，但它们忽略了地球空间的复杂性，如存在的不均质性和曲线几何。在这里，我们展示了由太阳风压力脉冲脉冲激发的共振波的全球MHD模拟。尽管表面、快速磁声(腔/波导)和Alfvén模的许多方面与盒和轴对称偶极子模型一致，但我们发现在现实的磁层中，对大尺度波的一些预测发生了显著变化。即使在单调波速下，快模式转折点和Alfvén共振位置的径向顺序也可能是相反的。不存在于位移/速度中的沿场线的附加节点出现在磁场的垂直分量和压缩分量中。在磁层顶附近，磁场的垂直振荡与速度相反。最后，广泛使用的驻波检测技术，无论是在场上还是在场上，都无法识别它们的存在。我们解释了当考虑非均匀背景场时，所有这些特征是如何从MHD方程中产生的，并提出了可能应用于航天器观测的改进方法。全球MHD模拟表明，系统尺度的ULF波的极化可能与BOX和偶极模型的预测有很大不同。由于高度不均匀的背景场，磁场中相对于速度的相位或惯用手反转可以简单地发生。我们提出了用于航天器观测的改进的探测技术，该技术考虑了真实磁层的影响
System‐scale magnetohydrodynamic (MHD) waves within Earth's magnetosphere are often understood theoretically using box models. While these have been highly instructive in understanding many fundamental features of the various wave modes present, they neglect the complexities of geospace such as the inhomogeneities and curvilinear geometries present. Here, we show global MHD simulations of resonant waves impulsively excited by a solar wind pressure pulse. Although many aspects of the surface, fast magnetosonic (cavity/waveguide), and Alfvén modes present agree with the box and axially symmetric dipole models, we find some predictions for large‐scale waves are significantly altered in a realistic magnetosphere. The radial ordering of fast mode turning points and Alfvén resonant locations may be reversed even with monotonic wave speeds. Additional nodes along field lines that are not present in the displacement/velocity occur in both the perpendicular and compressional components of the magnetic field. Close to the magnetopause, the perpendicular oscillations of the magnetic field have the opposite handedness to the velocity. Finally, widely used detection techniques for standing waves, both across and along the field, can fail to identify their presence. We explain how all these features arise from the MHD equations when accounting for a non‐uniform background field and propose modified methods that might be applied to spacecraft observations. A global MHD simulation shows system‐scale ULF waves' polarizations can significantly differ from box and dipole model predictions Phase or handedness reversals in the magnetic field compared to the velocity can occur simply due to the highly non‐uniform background field We propose modified detection techniques for spacecraft observations which account for the effects of a realistic magnetosphere