| Popis: |
Funding Information: Acknowledgements. We thank L. P. Chitta for useful discussions and J. de la Cruz Rodríguez for providing the data from 01 June 2015. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 695075) and has been supported by the BK21 plus program through the National Research Foundation (NRF) funded by the Ministry of Education of Korea. K.S. received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 797715, for a part of this project. J.S.C.D. was funded by the Deutscher Akademischer Austauschdienst (DAAD) and the International Max Planck Research School (IMPRS) for Solar System Science at the University of Göttingen. The 1.5-meter GREGOR solar telescope was built by a German consortium under the leadership of the Leibniz Institut für Sonnenphysik in Freiburg with the Leibniz Institut für Astrophysik Potsdam, the Institut für Astrophysik Göttingen, and the Max-Planck Institut für Sonnensystemforschung in Göttin-gen as partners, and with contributions by the Instituto de Astrofs´ica de Canarias and the Astronomical Institute of the Academy of Sciences of the Czech Republic. The GRIS instrument was developed thanks to the support by the Spanish Ministry of Economy and Competitiveness through the project AYA2010-18029 (Solar Magnetism and Astrophysical Spectropolarimetry). The data of 25 May 2015 were acquired by P. Gomory (PI of the campaign) and H. Balthasar within the SOLARNET Transnational Access and Service (TAS) program, which was supported by the European Commission’s FP7 Capacities Program under grant agreement No. 312495. GRIS data archive, SOLARNET and HiC campaigns are duly acknowledged. This study has made use of SAO-NASA Astrophysics Data System’s bibliographic services. Publisher Copyright: © 2022 K. Sowmya et al. The chromosphere above active regions (ARs) on the Sun hosts magnetized supersonic downflows. Studies of these supersonic downflows help to decipher the magnetic fine structure and dynamics of the chromosphere. We perform a statistical analysis of the magnetized supersonic downflows in a number of ARs at different evolutionary stages and survey their characteristics. We analyze spectro-polarimetric scans of parts of 13 ARs obtained in the infrared He I 10 830 triplet formed in the upper chromosphere recorded with the GREGOR Infrared Spectrograph mounted at the GREGOR solar telescope. We retrieve the line-of-sight velocities and the magnetic field vector using the HELIX+ inversion code that assumes Milne-Eddington atmospheres. We find magnetized supersonic downflows in all the ARs, with larger area coverage by such flows in ARs observed during their emerging phase. The fact that supersonic downflows were detected in all scans, albeit only covering a small fraction, 0.2 6.4%, of the observed field-of-view, suggests that they are a comparatively common phenomenon in the upper chromospheres of ARs. The supersonic downflows are found to be associated with many AR features, such as pores, sunspot umbrae, sunspot penumbrae, light bridges, plages, He I loops as part of arch filament systems characteristic of emerging fields, and filaments. Although several mechanisms are identified to be causing the supersonic downflows, by far the most common one appears to be the draining of plasma along the legs of rising magnetic loops. The loops mainly drain into forming pores. The line-of-sight velocities of the supersonic downflows reach values of up to 49 km s1, and the velocity distribution shows multiple populations. Almost 92% of these supersonic downflows coexist with a subsonic flow component. The weaker, more horizontal fields associated with the supersonic component suggests that it is formed above the subsonic component. |
