ULF wave transmission across collisionless shocks: 2.5D local hybrid simulations
ULF wave transmission across collisionless shocks: 2.5D local hybrid simulations
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无碰撞冲击中的 ULF 波传输：2.5D 局部混合模拟
DOI：
10.1029/2021ja029283
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
et al.
中科院分区：
文献类型：
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作者：
Kajdi;P.;Pfau-Kempf;Y.;Turc;L.;Dimmock;A. P.;Palmroth;M.;Takahashi;K.;et al.
我们通过分析 11 次 2D 局部混合模拟运行的输出来研究上游超低频 (ULF) 波与无碰撞冲击的相互作用。我们模拟的激波的阿尔夫尼马赫数在 4.29 到 7.42 之间，它们的角度为 、 、 和 。 ULF波前震在它们的上游发展。上游波的波长和振幅表现出对激波 和 的复杂依赖性。波长与这两个参数均呈正相关，且相关性更强。 ULF 波的振幅与反射光束速度和密度的乘积成正比，这也取决于 和 。 ULF波与激波的相互作用导致大规模（几十个上游离子惯性长度）激波波纹。冲击波纹的特性与超低频波的特性有关，即它们的波长和振幅。反过来，波纹对 ULF 波在激波上的传播有很大的影响，因为它们改变了局部激波特性（强度），使得同一 ULF 波前的不同部分遇到具有不同特性的激波。下游波动在波前延伸、方向或波长方面与上游波不同。然而，下游压缩波的傅里叶光谱中的一些特征是保守的，这些特征在与上游 ULF 波的波长大致对应的波长处呈现出凸起或平坦化。在横向下游光谱中，这些特征较弱。
We study the interaction of upstream ultralow frequency (ULF) waves with collisionless shocks by analyzing the outputs of 11 2D local hybrid simulation runs. Our simulated shocks have Alfvénic Mach numbers between 4.29 and 7.42 and their angles are , , , and . The ULF wave foreshocks develop upstream of all of them. The wavelength and the amplitude of the upstream waves exhibit a complex dependence on the shock's and . The wavelength positively correlates with both parameters, with the dependence on being much stronger. The amplitude of the ULF waves is proportional to the product of the reflected beam velocity and density, which also depend on and . The interaction of the ULF waves with the shock causes large‐scale (several tens of upstream ion inertial lengths) shock rippling. The properties of the shock ripples are related to the ULF wave properties, namely their wavelength and amplitude. In turn, the ripples have a large impact on the ULF wave transmission across the shock because they change local shock properties (, strength), so that different sections of the same ULF wavefront encounter shock with different characteristics. Downstream fluctuations do not resemble the upstream waves in terms the wavefront extension, orientation or their wavelength. However, some features are conserved in the Fourier spectra of downstream compressive waves that present a bump or flattening at wavelengths approximately corresponding to those of the upstream ULF waves. In the transverse downstream spectra, these features are weaker.