半年度衰减太阳活跃区域及其外围变暗区域的演变
Half-year Evolution of a Decaying Solar Active Region and Peripheral Dimming Regions
AI总结：
本研究通过多波长观测分析了太阳活跃区域NOAA AR 12738六个月内衰减过程，揭示了外围变暗区域的热亏损机制及其对日冕磁重构的影响。
摘要：
利用太阳动力学观测站（SDO）的多波长观测数据，我们研究了从2019年4月至10月六个月内太阳活跃区域NOAA AR 12738的衰减过程。我们通过分析极紫外（EUV）强度变化、量化磁通扩散以及通过差分发射测量（DEM）分析来系统研究该区域的演变。本研究首次对外围变暗区域（暗槽）进行了长期跟踪，揭示了其随时间持续减少的面积。DEM结果揭示了冷却等离子体的特征和热重构，变暗区域在10^5.5至10^5.9 K范围内表现出明显的温度亏损。潜在场外推确定了两种主要的磁配置：低处的环状结构带有冷却等离子体（<10^5.5 K）和连接到AR核心的高拱结构，导致局部发射减少。我们发现变暗主要由从AR核心延伸的高处环状结构引起，这些结构被加热到超过171Å通带的主要响应温度（>10^5.8 K），因此在典型的10^5.8 K形成温度处缺乏等离子体。热亏损，而不仅仅是物质的缺失，是减少发射的关键驱动因素。我们的结果表明，长期变暗为理解活跃区域衰减、热演变和日冕磁重构提供了有价值的诊断。
英文摘要：
Using multi-wavelength observations from the Solar Dynamics Observatory (SDO), we investigated the six-month decay process of the solar active region NOAA AR 12738 from April to October 2019. We systematically analyzed the region's evolution by examining extreme ultraviolet (EUV) intensity variations, quantifying magnetic flux diffusion, and investigating thermodynamic changes via Differential Emission Measure (DEM) analysis. This study presents the first long-term tracking of a peripheral dimming region (dark moat), revealing its continuous areal decrease over time. DEM results reveal cooling plasma signatures and thermal restructuring, with the dimming region exhibiting a distinct temperature deficit in range 10$^{5.5}$ -- 10$^{5.9}$~K. Potential field extrapolation identifies two dominant magnetic configurations: low-lying loops with cool plasma ($<$10$^{5.5}$ K), and high-arching structures connecting to the AR core, contributing to localized emission reduction. We found that the dimming is dominated by high-lying loops extending from the AR core, which are heated to temperatures above the main response of the 171~Å passband ($>$ 10$^{5.8}$ K), consequently lacking plasma at the typical 10$^{5.8}$~K formation temperature. The thermal deficit, not just the absence of material, is the key driver of the reduced emission. Our results demonstrate that long-duration dimming provides a valuable diagnostic for understanding active region decay, thermal evolution, and coronal magnetic restructuring.
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