Study of Global Photospheric and Chromospheric Flows Using Local Correlation Tracking and Machine Learning Methods I: Methodology and Uncertainty Estimates
Study of Global Photospheric and Chromospheric Flows Using Local Correlation Tracking and Machine Learning Methods I: Methodology and Uncertainty Estimates
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DOI：
10.1007/s11207-023-02158-x
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发表时间：
2023-05
期刊：
影响因子：
2.8
通讯作者：
Qin Li;Yan Xu;M. Verma;C. Denker;Junwei Zhao;Haimin Wang
中科院分区：
文献类型：
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作者：
Qin Li;Yan Xu;M. Verma;C. Denker;Junwei Zhao;Haimin Wang
太阳磁场的周期性变化，以及太阳活动的水平，是空间气象研究的最大兴趣之一。在描述太阳磁场起源和变化的太阳发电机中，全球尺度的表面流动，特别是差动自转和经向流动，起着重要的作用。原则上，差异旋转是偶极场形成和出现的根本原因，而经向流是将衰减场从低纬带到极地地区的纵向环流的表面成分。这种流动是太阳活动周期观测和模拟研究的关键输入和制约因素。在这里，我们提出了两种方法，局部相关跟踪(LCT)和基于机器学习的自监督光流方法，分别从探测光球层的全盘磁图和探测色球的图像中测量差异旋转和子午流。LCT在利用磁图推算光球流方面是稳健的。然而，我们发现，由于可跟踪特征的强烈动态性，它无法使用时序数据来跟踪流。光流法较好地处理了测量色球流场的数据。我们发现，来自光球和色球测量的差分旋转与赤道的最大值有很强的相关性，并且这种精度直到MDI和HMI数据集都有效。另一方面，由色球测量得到的经向流在最大纬度范围内与同时进行的光球测量呈现出相似的趋势。此外，还讨论了测量不确定度。
Cyclical variations of the solar magnetic fields, and hence the level of solar activity, are among the top interests of space weather research. Surface flows in global-scale, in particular differential rotation and meridional flows, play important roles in the solar dynamo that describes the origin and variation of solar magnetic fields. In principle, differential rotation is the fundamental cause of dipole field formation and emergence, and meridional flows are the surface component of a longitudinal circulation that brings decayed field from low latitudes to polar regions. Such flows are key inputs and constraints of observational and modeling studies of solar cycles. Here, we present two methods, local correlation tracking (LCT) and machine learning-based self-supervised optical flow methods, to measure differential rotation and meridional flows from full-disk magnetograms that probe the photosphere andimages that probe the chromosphere, respectively. LCT is robust in deriving photospheric flows using magnetograms. However, we found that it failed to trace flows using time-sequencedata because of the strong dynamics of traceable features. The optical flow methods handledata better to measure the chromospheric flow fields. We found that the differential rotation from photospheric and chromospheric measurements shows a strong correlation with a maximum ofat the equator and the accuracy holds untilfor the MDI and,for the HMI dataset. On the other hand, the meridional flow deduced from the chromospheric measurement shows a similar trend as the concurrent photospheric measurement withinwith a maximum ofatin latitude. Furthermore, the measurement uncertainties are discussed.