University of Oulu

Reconstructing solar magnetic fields from historical observations - VIII. AIA 1600 Å contrast as a proxy of solar magnetic fields I. Tähtinen, I. I. Virtanen, A. A. Pevtsov, K. Mursula, A&A 664 A2 (2022) DOI: 10.1051/0004-6361/202141164

Reconstructing solar magnetic fields from historical observations : VIII. AIA 1600 Å contrast as a proxy of solar magnetic fields

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Author: Tähtinen, Ismo1; Virtanen, I.I.1,2; Pevtsov, Alexei A.3;
Organizations: 1ReSoLVE Centre of Excellence, Space Physics and Astronomy research unit, University of Oulu, POB 8000, FI-90014, Oulu, Finland
2Oulu University of Applied Sciences, POB 222, FI-90101, Oulu, Finland
3National Solar Observatory, Boulder, CO 80303, USA
Format: article
Version: accepted version
Access: open
Online Access: PDF Full Text (PDF, 21.6 MB)
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Language: English
Published: EDP Sciences, 2022
Publish Date: 2022-10-27


Context: The bright regions in the solar chromosphere and temperature minimum have a good spatial correspondence with regions of intense photospheric magnetic field. Bright regions are visible in different emission lines and parts of the continuum. Their observation started more than a hundred years ago with the invention of the spectroheliograph. While the historical spectroheliograms are essential for studying the long-term variability of the Sun, the modern satellite-borne observations can help us reveal the nature of chromospheric brightenings in previously unattainable detail.

Aims: Our aim is to improve the understanding of the relation between magnetic fields and radiative structures byf studying modern seeing-free observations of far-ultraviolet (FUV) radiation around 1600 Å and photospheric magnetic fields.

Methods: We used Helioseismic and Magnetic Imager (HMI) observations of photospheric magnetic fields and Atmospheric Imaging Assembly (AIA) observations of FUV contrast around 1600 Å. We developed a robust method to find contrast thresholds defining bright and dark AIA 1600 Å pixels, and we combine them to bright and dark clusters. We investigate the relation of magnetic fields and AIA 1600 Å radiation in bright and dark clusters.

Results: We find that the percentage of bright pixels (ranging from 2% to 10%) almost entirely explains the observed variability of 1600 Å emission. We developed a multilinear regression model based on the percentages of bright and dark pixels, which can reliably predict the magnitude of the disk-averaged unsigned magnetic field. We find that bright and dark clusters closely correspond respectively to the populations of moderate ( B  >   55 G) and strong (B  >   1365 G) magnetic field HMI clusters. The largest bright clusters have a constant mean unsigned magnetic field, as found previously for Ca II K plages. However, the magnetic field strength of bright clusters is 254.7 ± 0.1 G, which is roughly 100 G larger than found earlier for Ca II K plages.

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Series: Astronomy and astrophysics
ISSN: 0004-6361
ISSN-E: 1432-0746
ISSN-L: 0004-6361
Volume: 664
Article number: A2
DOI: 10.1051/0004-6361/202141164
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: We acknowledge the financial support by the Academy of Finland to the ReSoLVE Centre of Excellence (project no. 307411). I.T acknowledges the financial support by the Academy of Finland to the PROSPECT (project no. 321440) and by the Finnish Academy of Science and Letters (Väisälä Fund).
Academy of Finland Grant Number: 307411
Detailed Information: 307411 (Academy of Finland Funding decision)
321440 (Academy of Finland Funding decision)
Copyright information: © The Author(s) 2022.