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  Average surface flows before the formation of solar active regions and their relationship to the supergranulation pattern

Birch, A., Schunker, H., Braun, D. C., & Gizon, L. (2019). Average surface flows before the formation of solar active regions and their relationship to the supergranulation pattern. Astronomy and Astrophysics, 628: A37. doi:10.1051/0004-6361/201935591.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0006-4F3B-1 Version Permalink: http://hdl.handle.net/21.11116/0000-0006-4F3C-0
Genre: Journal Article

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 Creators:
Birch, Aaron1, Author              
Schunker, Hannah1, Author              
Braun, D. C., Author
Gizon, Laurent1, Author              
Affiliations:
1Department Solar and Stellar Interiors, Max Planck Institute for Solar System Research, Max Planck Society, ou_1832287              

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 Abstract: Context. The emergence of solar active regions is an important but poorly understood aspect of the solar dynamo. Aims. Knowledge of the flows associated with the rise of active-region-forming magnetic concentrations through the near-surface layers will help determine the mechanisms of active region formation. Methods. We used helioseismic holography and granulation tracking to measure the horizontal flows at the surface that precede the emergence of active regions. We then averaged these flows over about sixty emerging active regions to reduce the noise, selecting active regions that emerge into relatively quiet Sun. To help interpret the results, we constructed a simple model flow field by generating synthetic “emergence locations” that are probabilistically related to the locations of supergranulation-scale convergence regions in the quiet Sun. Results. The flow maps obtained from helioseismology and granulation tracking are very similar (correlation coefficients for single maps around 0.96). We find that active region emergence is, on average, preceded by converging horizontal flows of amplitude about 40 m s−1. The convergence region extends over about 40 Mm in the east-west direction and about 20 Mm in the north-south direction and is centered in the retrograde direction relative to the emergence location. This flow pattern is largely reproduced by a model in which active region emergence occurs preferentially in the prograde direction relative to supergranulation inflows. Conclusions. Averaging over many active regions reveals a statistically significant pattern of near-surface flows prior to emergence. The qualitative success of our simple model suggests that rising flux concentrations and supergranule-scale flows interact during the emergence process.

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Language(s): eng - English
 Dates: 2019
 Publication Status: Published online
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Method: Peer
 Identifiers: DOI: 10.1051/0004-6361/201935591
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Title: Astronomy and Astrophysics
  Other : Astron. Astrophys.
Source Genre: Journal
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Publ. Info: Les Ulis Cedex A France : EDP Sciences
Pages: - Volume / Issue: 628 Sequence Number: A37 Start / End Page: - Identifier: Other: 1432-0746
ISSN: 0004-6361
CoNE: https://pure.mpg.de/cone/journals/resource/954922828219_1