快速变化颗粒激发脉冲波
Impulsive wave excitation by rapidly changing granules
摘要：
目前还没有完全了解太阳内部和大气中的磁流体动力学波是如何被激发的。传统上，湍流对流在内部被认为是在安静的太阳波激发的来源。在过去的几十年里，在光球层的颗粒间通道中观察到的声学事件已经成为波激发源的一个强有力的候选者。在这里，我们报告我们的观察波激发的一种新类型的事件：快速变化的颗粒。我们的观测是在大熊太阳天文台的1.6米古德太阳望远镜的H $α$和Ca II 8542 $\unicode{xC5}$线和TiO 7057 $\unicode{xC5}$宽带滤波成像器上用快速成像太阳光谱仪进行的。我们确定在互联网区域的颗粒，经历快速的动态变化，如崩溃（事件1），碎片化（事件2），或淹没（事件3）。在光球图像中，这些颗粒变得比相邻的颗粒明显更暗。在颗粒的快速变化之后，在光球层和色球层中检测到瞬态振荡。在事件1的情况下，振荡的主导周期是接近4.2分钟的光球和3.8分钟的色球。此外，在Ca II $-$ 0.5 $\unicode{xC5}$光栅图像中，我们观察到快速变化颗粒位置的重复增亮，这被认为是冲击波的表现。根据我们的研究结果，我们认为，颗粒的动态变化可以产生向上传播的声波在安静的太阳，最终发展成冲击。
英文摘要：
It is not yet fully understood how magnetohydrodynamic waves in the interior and atmosphere of the Sun are excited. Traditionally, turbulent convection in the interior is considered to be the source of wave excitation in the quiet Sun. Over the last few decades, acoustic events observed in the intergranular lanes in the photosphere have emerged as a strong candidate for a wave excitation source. Here we report our observations of wave excitation by a new type of event: rapidly changing granules. Our observations were carried out with the Fast Imaging Solar Spectrograph in the H$α$ and Ca II 8542 $\unicode{xC5}$ lines and the TiO 7057 $\unicode{xC5}$ broadband filter imager of the 1.6 m Goode Solar Telescope at the Big Bear Solar Observatory. We identify granules in the internetwork region that undergo rapid dynamic changes such as collapse (event 1), fragmentation (event 2), or submergence (event 3). In the photospheric images, these granules become significantly darker than neighboring granules. Following the granules' rapid changes, transient oscillations are detected in the photospheric and chromospheric layers. In the case of event 1, the dominant period of the oscillations is close to 4.2 min in the photosphere and 3.8 min in the chromosphere. Moreover, in the Ca II$-$0.5 $\unicode{xC5}$ raster image, we observe repetitive brightenings in the location of the rapidly changing granules that are considered the manifestation of shock waves. Based on our results, we suggest that dynamic changes of granules can generate upward-propagating acoustic waves in the quiet Sun that ultimately develop into shocks.
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