NDLI: Correlations between sunspots and their moat flows

Content Provider	EDP Sciences
Author	J. Löhner-Böttcher R. Schlichenmaier
Abstract	Context. The presence of the moat flow around sunspots is intimately linked to the mere existence of sunspots.Aims. We characterize the moat flow (MF) and Evershed flow (EF) in sunspots to enhance our knowledge of sunspot structures and photospheric flow properties.Methods. We calibrated HMI synoptic Doppler maps and used them to analyze 3 h time averages of 31 circular, stable, and fully developed sunspots at heliocentric angles of some 50°. Assuming axially symmetrical flow fields, we infer the azimuthally averaged horizontal velocity component of the MF and EF from 51 velocity maps. We studied the MF properties (velocity and extension) and elaborate on how these components depend on sunspot parameters (sunspot size and EF velocity). To explore the weekly and monthly evolution of MFs, we compare spots rotating from the eastern to western limbs and spots that reappear on the eastern limb.Results. Our calibration procedure of HMI Doppler maps yields reliable and consistent results. In 3 h averages, we find the MF decreases on average from some 1000 ± 200 m/s just outside the spot boundary to 500 m/s after an additional 4 Mm. The average MF extension lies at 9.2 ± 5 Mm, where the velocity drops below some 180 m/s. Neither the MF velocity nor its extension depend significantly on the sunspot size or EF velocity. But, the EF velocity does show a tendency to be enhanced with sunspot size. On a time scale of a week and a month, we find decreasing MF extensions and a tendency for the MF velocity to increase for strongly decaying sunspots, whereas the changing EF velocity has no impact on the MF.Conclusions. On 3 h averages, the EF velocity scales with the size of sunspots, while the MF properties show no significant correlation with the EF or with the sunspot size. This we interpret as a hint that the physical origins of EF and MF are distinct.
Page Count	13
File Format	HTM / HTML PDF
ISSN	00046361
Alternate Webpage(s)	https://www.aanda.org/articles/aa/abs/2013/03/aa20543-12/aa20543-12.html
e-ISSN	14320746
Journal	Astronomy & Astrophysics
Volume Number	551
DOI	10.1051/0004-6361/201220543
Language	English
Publisher	EDP Sciences
Publisher Date	2013-03-01
Access Restriction	Open
Rights Holder	© ESO, 2013
Subject Keyword	sunspots Sun: activity Sun: photosphere Sun: rotation convection techniques: radial velocities sunspots / Sun: activity / Sun: photosphere / Sun: rotation / convection / techniques: radial velocities
Content Type	Text
Resource Type	Article
Subject	Astronomy and Astrophysics Space and Planetary Science

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1	Ministry of Education (GoI), Department of Higher Education	Sanctioning Authority	https://www.education.gov.in/ict-initiatives
2	Indian Institute of Technology Kharagpur	Host Institute of the Project: The host institute of the project is responsible for providing infrastructure support and hosting the project	https://www.iitkgp.ac.in
3	National Digital Library of India Office, Indian Institute of Technology Kharagpur	The administrative and infrastructural headquarters of the project	Dr. B. Sutradhar bsutra@ndl.gov.in
4	Project PI / Joint PI	Principal Investigator and Joint Principal Investigators of the project	Dr. B. Sutradhar bsutra@ndl.gov.in Prof. Saswat Chakrabarti will be added soon
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