Temporal and Spatial Scales in Coronal Rain Revealed by UV Imaging and Spectroscopic Observations
Temporal and Spatial Scales in Coronal Rain Revealed by UV Imaging and Spectroscopic Observations
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紫外成像和光谱观测揭示日冕雨的时空尺度
DOI：
10.1007/s11207-020-01617-z
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发表时间：
2020
期刊：
影响因子：
2.8
通讯作者：
S.
中科院分区：
文献类型：
--
作者：
Ishikawa;R.T.;Katsukawa;Y.;Antolin;P.;and Toriumi;S.
日冕雨对应于日冕中向太阳表面聚集的冷而密集的团块;它经常在太阳活动区上方观察到。这些团块通常被认为是由日冕中的热不稳定性产生的，它们的寿命受到它们到达色球层的时间的限制。虽然雨通常在下落时分裂成较小的团块，但其具体的空间和时间尺度仍然不清楚。此外，雨与色球层的影响的观测特征还没有得到澄清。在这项研究中，我们调查的速度和强度的太阳黑子上方的日冕雨的时间演化分析的大气成像组件（AIA）获得的太阳动力学天文台（SDO）以及狭缝颚图像（SJIs）和光谱数据所采取的界面区域成像光谱仪（IRIS）卫星的日冕图像。我们确定黑暗和明亮的线程移动到本影在AIA图像和SJIs，分别和空间色球强度增强和红移在三个IRIS光谱线，Mgik 2796，Siiv 1394，和Cii 1336。强度增强和日冕雨红移几乎同时发生在所有三条谱线上，这清楚地表明了与日冕雨的因果关系。此外，我们检测到突发强度变化的时间尺度短于1分钟的Mgiik，Siiv和Cii，表明雨团的长度尺度约为2.7毫米，如果我们乘以典型的时间尺度的突发强度变化在30秒的雨速度。IRIS谱线的这种快速增强在时间分辨率限制的5.6秒的时滞内被激发。这些时间和空间尺度可以反映负责雨形态的物理过程，并暗示不稳定性，如开尔文-亥姆霍兹不稳定性。
Coronal rain corresponds to cool and dense clumps in the corona accreting towards the solar surface; it is often observed above solar active regions. These clumps are generally thought to be produced by a thermal instability in the corona and their lifetime is limited by the time they take to reach the chromosphere. Although the rain usually fragments into smaller clumps while falling down, their specific spatial and temporal scales remain unclear. In addition, the observational signatures of the impact of the rain with the chromosphere have not been clarified yet. In this study, we investigate the time evolution of the velocity and intensity of coronal rain above a sunspot by analyzing coronal images obtained by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) as well as the slit-jaw images (SJIs) and spectral data taken by the Interface Region Imaging Spectrograph (IRIS) satellite. We identify dark and bright threads moving towards the umbra in AIA images and in SJIs, respectively, and co-spatial chromospheric intensity enhancements and redshifts in three IRIS spectral lines, Mgiik 2796 Å, Siiv1394 Å, and Cii1336 Å. The intensity enhancements and coronal rain redshifts occur almost concurrently in all the three lines, which clearly demonstrates the causal relationship with coronal rain. Furthermore, we detect bursty intensity variation with a time scale shorter than 1 minute in Mgiik, Siiv, and Cii, indicating that a length scale of rain clumps is about 2.7 Mm if we multiply the typical time scale of the busty intensity variation at 30 sec by the rain velocity at. Such rapid enhancements in the IRIS lines are excited within a time lag of 5.6 sec limited by the temporal resolution. These temporal and spatial scales may reflect the physical processes responsible for the rain morphology, and are suggestive of instabilities such as the Kelvin–Helmholtz instability.