Auroral, Ionospheric and Ground Magnetic Signatures of Magnetopause Surface Modes
Auroral, Ionospheric and Ground Magnetic Signatures of Magnetopause Surface Modes
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DOI：
10.1029/2022ja031081
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发表时间：
2023-02
期刊：
影响因子：
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通讯作者：
M. Archer;M. Hartinger;L. Rastätter;D. Southwood;M. Heyns;J. Eggington;A. Wright;F. Plaschke;X. Shi
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文献类型：
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作者：
M. Archer;M. Hartinger;L. Rastätter;D. Southwood;M. Heyns;J. Eggington;A. Wright;F. Plaschke;X. Shi
地球磁层顶的面波对全球磁层动力学具有控制作用。由于航天器提供稀疏的原位观测点，因此需要在极地地区使用地面仪器对这些模式进行遥感。然而，关于预期签名的许多开放性概念问题仍然存在。因此，我们通过磁流体动力学理论和磁层顶表面本征模的全球耦合磁层-电离层模拟，提供了极光，电离层和地面磁观测中预期的关键定性特征的预测。这表明，由于表面模式及其非共振阿尔芬耦合，单色振荡场向电流（FACs）存在于整个磁层中。电流的峰值出现在磁层顶边界层的赤道边缘，而不是之前认为的开闭边界。他们也表现出缓慢的向极相运动，而不是纯粹的倏逝。我们认为，向上的FAC扰动可能会导致周期性的极光增亮。在电离层中，对流涡旋使向极移动的FAC结构循环。最后，表面模式信号预测在地面磁场中，电离层霍尔电流旋转扰动约（但不完全）90°的磁层相比。因此，典型的昼侧磁层顶表面模式应该在东西向地面磁场分量中最强。总的来说，磁层顶表面模式的所有地基特征被预测在L壳层上具有相同的频率，在磁层顶的赤道边缘附近最大化的振幅，以及比场线共振更大的纬度尺度。电离层焦耳加热和地磁感应电流的影响进行了讨论。
Surface waves on Earth's magnetopause have a controlling effect upon global magnetospheric dynamics. Since spacecraft provide sparse in situ observation points, remote sensing these modes using ground‐based instruments in the polar regions is desirable. However, many open conceptual questions on the expected signatures remain. Therefore, we provide predictions of key qualitative features expected in auroral, ionospheric, and ground magnetic observations through both magnetohydrodynamic theory and a global coupled magnetosphere‐ionosphere simulation of a magnetopause surface eigenmode. These show monochromatic oscillatory field‐aligned currents (FACs), due to both the surface mode and its non‐resonant Alfvén coupling, are present throughout the magnetosphere. The currents peak in amplitude at the equatorward edge of the magnetopause boundary layer, not the open‐closed boundary as previously thought. They also exhibit slow poleward phase motion rather than being purely evanescent. We suggest the upward FAC perturbations may result in periodic auroral brightenings. In the ionosphere, convection vortices circulate the poleward moving FAC structures. Finally, surface mode signals are predicted in the ground magnetic field, with ionospheric Hall currents rotating perturbations by approximately (but not exactly) 90° compared to the magnetosphere. Thus typical dayside magnetopause surface modes should be strongest in the East‐West ground magnetic field component. Overall, all ground‐based signatures of the magnetopause surface mode are predicted to have the same frequency across L‐shells, amplitudes that maximize near the magnetopause's equatorward edge, and larger latitudinal scales than for field line resonance. Implications in terms of ionospheric Joule heating and geomagnetically induced currents are discussed.