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Evolution of the magnetic field distribution of active regions

Dacie, S; Démoulin, P; Van Driel-Gesztelyi, L; Long, DM; Baker, D; Janvier, M; Yardley, SL; (2016) Evolution of the magnetic field distribution of active regions. Astronomy and Astrophysics , 596 (2016) , Article A69. 10.1051/0004-6361/201628948. Green open access

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Abstract

AIMS: Although the temporal evolution of active regions (ARs) is relatively well understood, the processes involved continue to be the subject of investigation. We study how the magnetic field of a series of ARs evolves with time to better characterise how ARs emerge and disperse. METHODS: We examined the temporal variation in the magnetic field distribution of 37 emerging ARs. A kernel density estimation plot of the field distribution was created on a log-log scale for each AR at each time step. We found that the central portion of the distribution is typically linear, and its slope was used to characterise the evolution of the magnetic field. RESULTS: The slopes were seen to evolve with time, becoming less steep as the fragmented emerging flux coalesces. The slopes reached a maximum value of ∼-1.5 just before the time of maximum flux before becoming steeper during the decay phase towards the quiet-Sun value of ∼-3. This behaviour differs significantly from a classical diffusion model, which produces a slope of -1. These results suggest that simple classical diffusion is not responsible for the observed changes in field distribution, but that other processes play a significant role in flux dispersion. CONCLUSIONS. We propose that the steep negative slope seen during the late-decay phase is due to magnetic flux reprocessing by (super)granular convective cells.

Type: Article
Title: Evolution of the magnetic field distribution of active regions
Open access status: An open access version is available from UCL Discovery
DOI: 10.1051/0004-6361/201628948
Publisher version: http://dx.doi.org/10.1051/0004-6361/201628948
Language: English
Additional information: © ESO, 2016.
Keywords: magnetic fields, Sun: photosphere, Sun: evolution, sunspotS, Methods: statistical, Methods: analytical.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/1531064
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