Further Evidence for Looplike Fine Structure Inside "Unipolar" Active Region Plages
Journal Article - Open Access
NAVAL RESEARCH LAB WASHINGTON DC WASHINGTON United States
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Earlier studies using extreme-ultraviolet images and line-of-sight magnetograms from the Solar Dynamics Observatory SDO have suggested that active region AR plages and strong network concentrations often have small, looplike features embedded within them, even though no minority-polarity flux is visible in the corresponding magnetograms. Because of the unexpected nature of these findings, we have searched the SDO database for examples of inverted-Y structures rooted inside unipolar plages, with such jetlike structures being interpreted as evidence for magnetic reconnection between small bipoles and the dominant-polarity field. Several illustrative cases are presented from the period of 20132015, all of which are associated with transient outflows from AR moss. The triangular or dome-shaped bases have horizontal dimensions of 24 Mm, corresponding to 13 granular diameters. We also note that the spongy-textured Fe ix 17.1 nm moss is not confined to plages, but may extend into regions where the photospheric field is relatively weak or even has mixed polarity. We again find a tendency for bright coronal loops seen in the 17.1, 19.3, and 21.1 nm passbands to show looplike fine structure and compact brightenings at their footpoints. These observations provide further confirmation that present-day magnetograms are significantly underrepresenting the amount of minority-polarity flux inside AR plages and again suggest that footpoint reconnection and small-scale flux cancellation may play a major role in coronal heating, both inside and outside ARs.