Study of Variations of Some Characteristics of the Giant Coronal Hole of 2015–2017
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Analysis of images of the full solar disk obtained by ground-based (BST-2, CrAO RAS) and space-based (SDO/AIA, SDO/HMI) instruments and the potential approximation method revealed some features of the evolution of a long-lived coronal hole (CH) of 2015–2017. Variations in such CH characteristics as the area, intensity, magnetic field (MF) strength, and magnetic flux are studied. The study of the change in the area and average intensity of the CH contour at different heights has shown that changes in its area throughout the entire period occur almost synchronously within the boundaries determined by model calculations at the photospheric level and by observations of the Sun in the chromosphere and corona. The average CH intensity depends on the moment of its evolution: it varies from the intensity of the undisturbed region to the CH maximum intensity. This process lasts about the same time as the increase in the CH area. The intensity of the He I 10830 Å (He I) line occurs in antiphase with the decrease in the intensity in the Fe XII 193Å (Fe XII) line. This paper shows that this CH has significantly reduced the magnetic flux in a large part of the Sun in a time interval of almost a year and a half. Even when the CH began to collapse noticeably, the magnetic field strength and the magnetic flux continued to decrease.
This study was supported in part by the Russian Foundation for Basic Research, project nos. 16-42-910467 r_a and 17-42-92017 r_a.
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