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PROPERTIES OF SUPERSONIC EVERSHED DOWNFLOWS
Stockholm University, Faculty of Science, Department of Astronomy. CSIC, Spain.
Stockholm University, Faculty of Science, Department of Astronomy.
Number of Authors: 32016 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 832, no 2, article id 170Article in journal (Refereed) Published
Abstract [en]

We study supersonic Evershed downflows in a sunspot penumbra by means of high spatial resolution spectropolarimetric data acquired in the Fe I. 617.3 nm line with the CRISP instrument at the Swedish 1 m Solar Telescope. Physical observables, such as Dopplergrams calculated from line bisectors and Stokes. V zero-crossing wavelengths, and Stokes. V maps in the far red-wing, are used to find regions where supersonic Evershed downflows may exist. We retrieve the line-of-sight velocity and the magnetic field vector in these regions using two-component inversions of the observed Stokes profiles with the help of the SIR code. We follow these regions during their lifetime to study their temporal behavior. Finally, we carry out a statistical analysis of the detected supersonic downflows to characterize their physical properties. Supersonic downflows are contained in compact patches moving outward, which are located in the mid-and outer penumbra. They are observed as bright, roundish structures at the outer end of penumbral filaments that resemble penumbral grains. The patches may undergo fragmentations and mergings during their lifetime; some of them are recurrent. Supersonic downflows are associated with strong and rather vertical magnetic fields with a reversed polarity compared to that of the sunspot. Our results suggest that downflows returning back to the solar surface with supersonic velocities are abruptly stopped in dense deep layers and produce a shock. Consequently, this shock enhances the temperature and is detected as a bright grain in the continuum filtergrams, which could explain the existence of outward-moving grains in the mid-and outer penumbra.

Place, publisher, year, edition, pages
2016. Vol. 832, no 2, article id 170
Keywords [en]
methods: observational, Sun: atmosphere, Sun: photosphere, sunspots, techniques: polarimetric
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:su:diva-139298DOI: 10.3847/0004-637X/832/2/170ISI: 000390490100030OAI: oai:DiVA.org:su-139298DiVA, id: diva2:1074442
Available from: 2017-02-15 Created: 2017-02-15 Last updated: 2017-11-29Bibliographically approved

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