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  Magnetic Reconnection at the Earliest Stage of Solar Flux Emergence

Tian, H., Zhu, X., Peter, H., Zhao, J., Samanta, T., & Chen, Y. (2018). Magnetic Reconnection at the Earliest Stage of Solar Flux Emergence. Astrophysical Journal, 854(2): 174. doi:10.3847/1538-4357/aaaae6.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0003-31E3-5 Version Permalink: http://hdl.handle.net/21.11116/0000-0003-31E4-4
Genre: Journal Article

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 Creators:
Tian, Hui, Author
Zhu, Xiaoshuai1, Author
Peter, Hardi1, Author              
Zhao, Jie, Author
Samanta, Tanmoy, Author
Chen, Yajie, Author
Affiliations:
1Department Sun and Heliosphere, Max Planck Institute for Solar System Research, Max Planck Society, ou_1832289              

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Free keywords: magnetic reconnection; Sun: chromosphere; Sun: transition region; Sun: UV radiation; sunspots
 Abstract: On 2016 September 20, the Interface Region Imaging Spectrograph observed an active region during its earliest emerging phase for almost 7 hr. The Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory observed continuous emergence of small-scale magnetic bipoles with a rate of ~1016 Mx s−1. The emergence of magnetic fluxes and interactions between different polarities lead to the frequent occurrence of ultraviolet (UV) bursts, which exhibit as intense transient brightenings in the 1400 Å images. In the meantime, discrete small patches with the same magnetic polarity tend to move together and merge, leading to the enhancement of the magnetic fields and thus the formation of pores (small sunspots) at some locations. The spectra of these UV bursts are characterized by the superposition of several chromospheric absorption lines on the greatly broadened profiles of some emission lines formed at typical transition region temperatures, suggesting heating of the local materials to a few tens of thousands of kelvin in the lower atmosphere by magnetic reconnection. Some bursts reveal blue- and redshifts of ~100 km s−1 at neighboring pixels, indicating the spatially resolved bidirectional reconnection outflows. Many such bursts appear to be associated with the cancellation of magnetic fluxes with a rate of the order of ~1015 Mx s−1. We also investigate the three-dimensional magnetic field topology through a magnetohydrostatic model and find that a small fraction of the bursts are associated with bald patches (magnetic dips). Finally, we find that almost all bursts are located in regions of large squashing factor at the height of ~1 Mm, reinforcing our conclusion that these bursts are produced through reconnection in the lower atmosphere.

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Language(s): eng - English
 Dates: 2019-03-192018
 Publication Status: Published online
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.3847/1538-4357/aaaae6
 Degree: -

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Title: Astrophysical Journal
Source Genre: Journal
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Publ. Info: Chicago, IL : University of Chicago Press for the American Astronomical Society
Pages: - Volume / Issue: 854 (2) Sequence Number: 174 Start / End Page: - Identifier: ISSN: 0004-637X
CoNE: https://pure.mpg.de/cone/journals/resource/954922828215_2