The Missing Cool Corona in the Flat Magnetic Field around Solar Active Regions
The Missing Cool Corona in the Flat Magnetic Field around Solar Active Regions
复制标题
太阳活动区域周围平坦磁场中缺失的冷日冕
DOI：
10.3847/1538-4357/abd7f2
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
R. Moore
中科院分区：
文献类型：
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作者：
T. Singh;A. Sterling;R. Moore
太阳动力学天文台/大气成像装置在几个极紫外波段对整个太阳盘成像，每个波段对一个或多个特定温度的日冕等离子体发射敏感。我们观察到，当孤立的活动区域（AR）在磁盘上，在一些冠状EUV通道的全磁盘图像显示AR的外围作为一个黑暗的护城河周围的AR。在这里，我们提出了七个具体的例子，从时间段选择时，只有一个单一的AR存在于磁盘上。在视觉上，我们观察到壕沟在AIA 171 λ谱带中最突出，该谱带在log 10 T = 5.8时对来自等离子体的发射最敏感。通过检查从六个AIA EUV通道发现的1D视线发射测量温度分布，我们发现护城河的强度在大多数情况下在log 10 T = 5.7-6.2的温度范围内最低。我们认为，黑暗护城河的存在是因为来自AR的强磁场的压力向下压在下面的磁环上，将这些磁环以及AR在护城河上的最低圈压平到低海拔。根据Antiochos和Noci的说法，这些环通常会发射大部分171的发射，但仅限于表面以上的高度，这些高度太低，无法在其中维持171的发射等离子体，而更热的EUV发射等离子体则维持在更高海拔的长AR-根日冕环中。这可能解释了AR周围的低冠温黑暗护城河。
Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) images the full solar disk in several extreme-ultraviolet (EUV) bands that are each sensitive to coronal plasma emissions of one or more specific temperatures. We observe that when isolated active regions (ARs) are on the disk, full-disk images in some of the coronal EUV channels show the outskirts of the AR as a dark moat surrounding the AR. Here we present seven specific examples, selected from time periods when there was only a single AR present on the disk. Visually, we observe the moat to be most prominent in the AIA 171 Å band, which has the most sensitivity to emission from plasma at log10 T = 5.8. By examining the 1D line-of-sight emission measure temperature distribution found from six AIA EUV channels, we find the intensity of the moat to be most depressed over the temperature range log10 T ≈ 5.7–6.2 for most of the cases. We argue that the dark moat exists because the pressure from the strong magnetic field that splays out from the AR presses down on underlying magnetic loops, flattening those loops—along with the lowest of the AR’s own loops over the moat—to a low altitude. Those loops, which would normally emit the bulk of the 171 Å emission, are restricted to heights above the surface that are too low to have 171 Å emitting plasmas sustained in them, according to Antiochos & Noci, while hotter EUV-emitting plasmas are sustained in the overlying higher-altitude long AR-rooted coronal loops. This potentially explains the low-coronal-temperature dark moats surrounding the ARs.