The centroid speed as a characteristic of the group speed of solar coronal fast magnetoacoustic wave trains
The centroid speed as a characteristic of the group speed of solar coronal fast magnetoacoustic wave trains
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质心速度作为太阳日冕快磁声波列群速度的特征
DOI：
10.1093/mnras/stad3681
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发表时间：
2024
影响因子：
4.8
通讯作者：
Kolotkov D
中科院分区：
文献类型：
--
作者：
Kolotkov D
日冕等离子体的高度丝状性质显着影响日冕的动态过程，例如磁流体动力波和振荡。由日冕等离子体不均匀性引导的快速磁声波表现出强烈的几何色散，形成准周期快速传播（QFP）波列。 QFP 波列可以在极紫外成像数据中观察到，也可以在微波和低频无线电中间接观察到，有助于了解日冕中的磁连通性、能量和质量传输。然而，由于波列包络的强色散和相关的快速演化，测量 QFP 波列的场对准群速度作为地震分析的关键参数具有挑战性。我们证明，在平面低β日冕等离子体不均匀性中形成的QFP波列的群速度可以通过波列有效质心（称为波列质心速度）的传播来评估。该质心速度作为一个潜在的可观测值，根据经验表明对应于波列中最具能量的傅里叶谐波的群速度。发现质心速度对与环境电晕的波导密度对比几乎不敏感，并且随着横向密度分布的陡度而变化。作为群速度测量的质心速度与相应波长的相速度之间的差异显示达到 70%，这对于能通量估计和观测结果的解释至关重要。
The highly filamented nature of the coronal plasma significantly influences dynamic processes in the corona such as magnetohydrodynamic waves and oscillations. Fast magnetoacoustic waves, guided by coronal plasma non-uniformities, exhibit strong geometric dispersion, forming quasi-periodic fast-propagating (QFP) wave trains. QFP wave trains are observed in extreme-ultraviolet imaging data and indirectly in microwaves and low-frequency radio, aiding in understanding the magnetic connectivity, energy, and mass transport in the corona. However, measuring the field-aligned group speed of QFP wave trains, as a key parameter for seismological analysis, is challenging due to strong dispersion and associated rapid evolution of the wave train envelope. We demonstrate that the group speed of QFP wave trains formed in plane low-β coronal plasma non-uniformities can be assessed through the propagation of the wave train’s effective centre of mass, referred to as the wave train’s centroid speed. This centroid speed, as a potential observable, is shown empirically to correspond to the group speed of the most energetic Fourier harmonic in the wave train. The centroid speed is found to be almost insensitive to the waveguide density contrast with the ambient corona, and to vary with the steepness of the transverse density profile. The discrepancy between the centroid speed as the group speed measure and the phase speed at the corresponding wavelength is shown to reach 70 per cent, which is crucial for the energy flux estimation and interpretation of observations.