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Detection of Convective Downflows in a Sunspot Penumbra
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
2011 (English)In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 333, no 6040, 316-319 p.Article in journal (Refereed) Published
Abstract [en]

The fine structure and dynamics of sunspots and the strong outflow in their outer filamentary part-the penumbra-have puzzled astronomers for more than a century. Recent theoretical models and three-dimensional numerical simulations explain the penumbral filaments and their radiative energy output as the result of overturning convection. Here, we describe the detection of ubiquitous, relatively dark downward flows of up to 1 kilometer per second (km/s) in the interior penumbra, using imaging spectropolarimetric data from the Swedish 1-meter Solar Telescope. The dark downflows are omnipresent in the interior penumbra, distinguishing them from flows in arched flux tubes, and are associated with strong (3 to 3.5 km/s) radial outflows. They are thus part of a penumbral convective flow pattern, with the Evershed flow representing the horizontal component of that convection.

Place, publisher, year, edition, pages
2011. Vol. 333, no 6040, 316-319 p.
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:su:diva-66577DOI: 10.1126/science.1206429ISI: 000292732000035OAI: oai:DiVA.org:su-66577DiVA: diva2:468623
Note
authorCount :4Available from: 2011-12-21 Created: 2011-12-20 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Three-dimensional mapping of fine structure in the solar atmosphere
Open this publication in new window or tab >>Three-dimensional mapping of fine structure in the solar atmosphere
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The effects on image formation through a tilted interference filter in a converging beam are investigated and an adequate compensation procedure is established. A method that compensates for small-scale seeing distortions is also developed with the aim of co-aligning non-simultaneous solar images from different passbands. These techniques are applied to data acquired with a narrow tiltable filter at the Swedish 1-meter Solar Telescope. Tilting provides a way to scan the wing of the Ca II H line. The resulting images are used to map the temperature stratification and vertical temperature gradients in a solar active region containing a sunspot at a resolution approaching 0''10. The data are compared with hydro-dynamical quiet sun models and magneto-hydrodynamic models of plage. The comparison gives credence to the observational techniques, the analysis methods, and the simulations. Vertical temperature gradients are lower in magnetic structures than in non-magnetic.

Line-of-sight velocities and magnetic field properties in the penumbra of the same sunspot are estimated using the CRISP imaging spectropolarimeter and straylight compensation adequate for the data. These reveal a pattern of upflows and downflows throughout the entire penumbra including the interior penumbra. A correlation with intensity positively identifies these flows as convective in origin. The vertical convective signatures are observed everywhere, but the horizontal Evershed flow is observed to be confined to areas of nearly horizontal magnetic field. 

The relation between temperature gradient and total circular polarization in magnetically sensitive lines is investigated in different structures of the penumbra. Penumbral dark cores are prominent in total circular polarization and temperature gradient maps. These become longer and more contiguous with increasing height. Dark fibril structures over bright regions are observed in the Ca II H line core, above both the umbra and penumbra.

Place, publisher, year, edition, pages
Stockholm: Department of Astronomy, Stockholm University, 2013. 41 p.
Keyword
Sun, sunspots, Swedish 1-meter Solar Telescope, active regions, image processing, sunspot penumbra
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-86798 (URN)978-91-7447-634-7 (ISBN)
Public defence
2013-02-15, sal FB52, Albanova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.

Available from: 2013-01-24 Created: 2013-01-18 Last updated: 2013-01-24Bibliographically approved

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