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1. What Causes Faint Solar Coronal Jets from Emerging Flux Regions in Coronal Holes?

   https://doi.org/10.3847/1538-4357/abee19  

   Harden, Abigail R.; Panesar, Navdeep K.; Moore, Ronald L.; Sterling, Alphonse C.; Adams, Mitzi L. (May 2021, The Astrophysical Journal)

   null (Ed.)
2. The chromospheric component of coronal bright points: Coronal and chromospheric responses to magnetic-flux emergence

   https://doi.org/10.1051/0004-6361/202039329  

   Madjarska, Maria S.; Chae, Jongchul; Moreno-Insertis, Fernando; Hou, Zhenyong; Nóbrega-Siverio, Daniel; Kwak, Hannah; Galsgaard, Klaus; Cho, Kyuhyoun (February 2021, Astronomy & Astrophysics)

   Context. We investigate the chromospheric counterpart of small-scale coronal loops constituting a coronal bright point (CBP) and its response to a photospheric magnetic-flux increase accompanied by co-temporal CBP heating. Aims. The aim of this study is to simultaneously investigate the chromospheric and coronal layers associated with a CBP, and in so doing, provide further understanding on the heating of plasmas confined in small-scale loops. Methods. We used co-observations from the Atmospheric Imaging Assembly and Helioseismic Magnetic Imager on board the Solar Dynamics Observatory, together with data from the Fast Imaging Solar Spectrograph taken in the H α and Ca  II 8542.1 Å lines. We also employed both linear force-free and potential field extrapolation models to investigate the magnetic topology of the CBP loops and the overlying corona, respectively. We used a new multi-layer spectral inversion technique to derive the temporal variations of the temperature of the H α loops (HLs). Results. We find that the counterpart of the CBP, as seen at chromospheric temperatures, is composed of a bundle of dark elongated features named in this work H α loops, which constitute an integral part of the CBP loop magnetic structure. An increase in the photospheric magnetic flux due to flux emergence is accompanied by a rise of the coronal emission of the CBP loops, that is a heating episode. We also observe enhanced chromospheric activity associated with the occurrence of new HLs and mottles. While the coronal emission and magnetic flux increases appear to be co-temporal, the response of the H α counterpart of the CBP occurs with a small delay of less than 3 min. A sharp temperature increase is found in one of the HLs and in one of the CBP footpoints estimated at 46% and 55% with respect to the pre-event values, also starting with a delay of less than 3 min following the coronal heating episode. The low-lying CBP loop structure remains non-potential for the entire observing period. The magnetic topological analysis of the overlying corona reveals the presence of a coronal null point at the beginning and towards the end of the heating episode. Conclusions. The delay in the response of the chromospheric counterpart of the CBP suggests that the heating may have occurred at coronal heights. 

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3. Emerging Dimming as Coronal Heating Episodes

   https://doi.org/10.3847/1538-4357/abee8d  

   Payne, Anna V.; Sun, Xudong (April 2021, The Astrophysical Journal)

   Abstract Emerging dimming occurs in isolated solar active regions (ARs) during the early stages of magnetic flux emergence. Observed by the Atmospheric Imaging Assembly, it features a rapid decrease in extreme-ultraviolet (EUV) emission in the 171 Å channel images, and a simultaneous increase in the 211 Å images. Here, we analyze the coronal thermodynamic and magnetic properties to probe its physical origin. We calculate the time-dependent differential emission measures for a sample of 18 events between 2010 and 2012. The emission measure (EM) decrease in the temperature range is well correlated with the EM increase in over eight orders of magnitude. This suggests that the coronal plasma is being heated from the quiet-Sun, sub-MK temperature to 1–2 MK, more typical for ARs. Potential field extrapolation indicates significant change in the local magnetic connectivity: the dimming region is now linked to the newly emerged flux via longer loops. We conclude that emerging dimming is likely caused by coronal heating episodes, powered by reconnection between the emerging and the ambient magnetic fields. 

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4. Flux Calibration of Coronal Magnetic Field

   https://doi.org/10.1007/s11207-024-02364-1  

   Vandas, Marek; Romashets, Evgeny (August 2024, Solar Physics)

   Leblaher, John (Ed.)

   Abstract Romashets and Vandas (2024) derived a method for the determination of Euler potentials at a spherical surface and applied it to the geomagnetic field. Here, we apply it to find Euler potentials at the source surface. A regular mesh defined by Euler potentials divides the source surface to surface elements with the same magnetic flux. By tracing magnetic-field lines away from the source surface, Euler potentials can be extended into the heliosphere. 

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5. ngVLA Observations of Coronal Magnetic Fields

   G. D. Fleishman, G. M. (December 2018, Science with a Next-Generation Very Large Array ASP Conference Series, Monograph 7)

   Energy stored in the magnetic field in the solar atmosphere above active regions is a key driver of all solar activity (e.g., solar flares and coronal mass ejections), some of which can affect life on Earth. Radio observations provide a unique diagnostic of the coronal magnetic fields that make them a critical tool for the study of these phenomena, using the technique of broadband radio imaging spectropolarimetry. Observations with the ngVLA will provide unique observations of coronal magnetic fields and their evolution, key inputs and constraints for MHD numerical models of the solar atmosphere and eruptive processes, and a key link between lower layers of the solar atmosphere and the heliosphere. In doing so they will also provide practical "research to operations" guidance for space weather forecasting. 

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