Further Evidence for Looplike Fine Structure inside "Unipolar" Active Region Plages

Abstract

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 2013--2015, all of which are associated with transient outflows from AR "moss." The triangular or dome-shaped bases have horizontal dimensions of $\sim$2--4 Mm, corresponding to $\sim$1--3 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.

References in corpus (9)

• Observables Processing for the Helioseismic and Magnetic Imager Instrument on the Solar Dynamics Observatory
• Structure of solar coronal loops: from miniature to large-scale
• A Cancellation Nanoflare Model for Solar Chromospheric and Coronal Heating
• Active region transition region loop populations and their relationship to the corona
• Solar Coronal Loops Associated with Small-scale Mixed Polarity Surface Magnetic Fields
• Observational Signatures of Coronal Loop Heating and Cooling Driven by Footpoint Shuffling
• A Cancellation Nanoflare Model for Solar Chromospheric and Coronal Heating II. 2D Theory and Simulations
• Miniature loops in the solar corona
• Energetics of magnetic transients in a solar active region plage

Cited by in corpus (9)

• Critical Science Plan for the Daniel K. Inouye Solar Telescope (DKIST)
• Small-scale Flux Emergence, Coronal Hole Heating, and Flux-tube Expansion: A Hybrid Solar Wind Model
• A Cancellation Nanoflare Model for Solar Chromospheric and Coronal Heating III. 3D Simulations and Atmospheric Response
• Measurements of Photospheric and Chromospheric Magnetic Field Structures Associated with Chromospheric Heating over a Solar Plage Region
• An ultra-long and quite thin coronal loop without significant expansion
• Undetected Minority-polarity Flux as the Missing Link in Coronal Heating
• Morphological evidence for nanoflares heating warm loops in the solar corona
• Magnetically coupled atmosphere, fast sausage MHD waves, and forced magnetic field reconnection during the SOL2014-09-10T17:45 flare
• Light Bridges Can Suppress the Formation of Coronal Loops