Fig. 3.
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Different CHs located in the disk centre. These CHs, which tend to appear in more active periods of the Sun, often exhibit circular or elliptic shapes or a combination of these basic geometries. CATCH (Heinemann et al. 2019) was used to detect the boundaries of these CHs, whose outline is marked in each panel by red curves. The background images were obtained with SDO/AIA in the 19.3 nm passband.
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