An Inside Look at Sunspot Oscillations with Higher Azimuthal Wavenumbers
An Inside Look at Sunspot Oscillations with Higher Azimuthal Wavenumbers
复制标题
DOI：
10.3847/1538-4357/aa73d6
复制
发表时间：
2017-06-10
影响因子：
4.9
通讯作者：
Christian, Damian J.
中科院分区：
文献类型：
--
作者：
Jess, David B.;Van Doorsselaere, Tom;Christian, Damian J.
太阳黑子本影的太阳色球观测提供了磁流体波现象的特殊视角。近年来，与传播的磁声模式相关的丰富的波特征被提出，这些特征揭示了波成分的复杂的时空结构。理论模型已经证明了这些无处不在的波是如何与m=0慢磁声模相一致的，该慢磁声模是由捕获的亚光球声(p模)波激发的。然而，本影波的频谱很宽，这表明观察到的特征代表了许多频率和/或模式的叠加。我们在空间域和时间域应用傅里叶滤波来提取与m=1慢磁声模式一致的色球本影波特征。这一身份以前从未被描述过。在空间波数为0.45<；k<；0.90arcsec(-1)的范围内，发现了m=1模的角频率为0.037+/-0.007 rad的S(-1)(2.1+/-0.4°S(-1)，对应的周期约为1 70 S)。求解了理论色散关系，并计算了相应的本征函数，从而可以研究密度微扰，并与我们的观测结果进行比较。这种磁流体力学模型证实了我们的解释，即所识别的波特征是太阳黑子色球本影中m=1慢磁声模的第一次直接观测。
Solar chromospheric observations of sunspot umbrae offer an exceptional view of magnetohydrodynamic wave phenomena. In recent years, a wealth of wave signatures related to propagating magneto-acoustic modes have been presented, which demonstrate complex spatial and temporal structuring of the wave components. Theoretical modeling has demonstrated how these ubiquitous waves are consistent with an m = 0 slow magneto-acoustic mode, which is excited by trapped sub-photospheric acoustic (p-mode) waves. However, the spectrum of umbral waves is broad, suggesting that the observed signatures represent the superposition of numerous frequencies and/or modes. We apply Fourier filtering, in both spatial and temporal domains, to extract chromospheric umbral wave characteristics consistent with an m = 1 slow magneto-acoustic mode. This identification has not been described before. Angular frequencies of 0.037 +/- 0.007 rad s(-1) (2.1 +/- 0.4 deg s(-1), corresponding to a period approximate to 170 s) for the m = 1 mode are uncovered for spatial wavenumbers in the range of 0.45 < k < 0.90 arcsec(-1) (5000-9000 km). Theoretical dispersion relations are solved, with corresponding eigenfunctions computed, which allows the density perturbations to be investigated and compared with our observations. Such magnetohydrodynamic modeling confirms our interpretation that the identified wave signatures are the first direct observations of an m = 1 slow magneto-acoustic mode in the chromospheric umbra of a sunspot.