High-frequency Oscillations in the Atmosphere above a Sunspot Umbra
High-frequency Oscillations in the Atmosphere above a Sunspot Umbra
复制标题
太阳黑子本影上方大气中的高频振荡
DOI：
10.3847/2041-8213/aab4f3
复制
发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Wang Rui
中科院分区：
文献类型：
--
作者：
Wang Feng;Deng Hui;Li Bo;Feng Song;Bai Xianyong;Deng Linhua;Yang Yunfei;Xue Zhike;Wang Rui
我们使用高空间和时间分辨率的观测，同时获得与新的真空太阳望远镜和大气成像组件（AIA）上的太阳动力学天文台，调查太阳黑子本影以上的高频振荡。采用一种新的时频分析方法--同步压缩变换（SST）来表征它们的功率谱，并重建不同太阳大气层的高频信号。与合成信号的验证研究表明，SST是能够解决弱信号，即使他们的强度是相当的高频噪声。从SST和傅里叶变换得到的整个本影区的功率谱表明，在不同的大气层中，在10和14 mHz（标记为12 mHz）之间有显着的增强。分析远离本影的光球区域的光谱表明，这12兆赫的分量只存在于本影内部。基于AIA 171中重建的12 mHz分量的动画显示，间歇传播的波首先出现在日冕扇结构的足点附近，然后沿沿着结构向外传播。时间-距离图，加上亚音速（1.49 km s-1），突出了这样一个事实，即这些日冕扰动最好被描述为向上传播的磁声慢波。因此，我们首次揭示了在本影以上不同高度的成像观测中周期约为一分钟的高频振荡，这些振荡似乎与光球中的本影扰动有关。
We use high spatial and temporal resolution observations, simultaneously obtained with the New Vacuum Solar Telescope and Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, to investigate the high-frequency oscillations above a sunspot umbra. A novel time–frequency analysis method, namely, the synchrosqueezing transform (SST), is employed to represent their power spectra and to reconstruct the high-frequency signals at different solar atmospheric layers. A validation study with synthetic signals demonstrates that SST is capable of resolving weak signals even when their strength is comparable to the high-frequency noise. The power spectra, obtained from both SST and the Fourier transform, of the entire umbral region indicate that there are significant enhancements between 10 and 14 mHz (labeled as 12 mHz) at different atmospheric layers. Analyzing the spectrum of a photospheric region far away from the umbra demonstrates that this 12 mHz component exists only inside the umbra. The animation based on the reconstructed 12 mHz component in AIA 171 Å illustrates that an intermittently propagating wave first emerges near the footpoints of coronal fan structures, and then propagates outward along the structures. A time–distance diagram, coupled with a subsonic wave speed (∼49 km s−1), highlights the fact that these coronal perturbations are best described as upwardly propagating magnetoacoustic slow waves. Thus, we first reveal the high-frequency oscillations with a period around one minute in imaging observations at different height above an umbra, and these oscillations seem to be related to the umbral perturbations in the photosphere.