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Chromospheric Evershed flow

Georgakilas, A. A. and Christopoulou, E. B. and Skodras, A. and Koutchmy, S. (2003) Chromospheric Evershed flow. Astronomy & Astrophysics, 403 (3). pp. 1123-1133. ISSN 0004-6361. doi:10.1051/0004-6361:20030385.

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We studied the chromospheric Evershed flow from filtergrams obtained at nine wavelengths along the Hα profile. We computed line-of-sight velocities based on Becker's cloud model and we determined the components of the flow velocity vector as a function of distance from the center of the sunspot, assuming an axial symmetry of both the spot and the flow. We found that the flow velocity decreases with decreasing height and that the maximum of the velocity shifts towards the inner penumbral boundary. The flow related to some fibrils deviates significantly from the average Evershed flow. The profile of the magnitude of the flow velocity as a function of distance from the spot center, indicates that the velocity attains its maximum value in the downstream part of the flow channels (assumed to have the form of a loop). This behavior can be understood in terms of a critical flow that pass from subsonic to supersonic near the apex of the loop, attains its higher velocity at the downstream part of the loop and finally relaxes to subsonic through a tube shock. We computed the average flow vector from segmented line-of-sight velocity maps, excluding bright or dark fibrils alternatively. We found that the radial component of the velocity does not show a significant difference, but the magnitude of the vertical component of the velocity related to dark fibrils is higher than that related to bright fibrils.

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Additional Information:© 2003 ESO. Received: 10 September 2002. Accepted: 27 February 2003. We would like to thank Dr. R. N. Smartt, the T.A.C. of NSO/SP and the staff of the Sacramento Peak Observatory, especially the Observers team of the DST, for their warm hospitality and their help with the observations. We also thank the referee, Dr. R. Schlichenmaier, for constructive criticism.
Subject Keywords:Sun: sunspots - Sun: chromosphere - magnetohydrodynamics (MHD) - techniques: image processing
Issue or Number:3
Record Number:CaltechAUTHORS:20180228-110821176
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Official Citation:Chromospheric Evershed flow A. A. Georgakilas, E. B. Christopoulou, A. Skodras and S. Koutchmy A&A, 403 3 (2003) 1123-1133 DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:85010
Deposited By: Ruth Sustaita
Deposited On:28 Feb 2018 19:48
Last Modified:15 Nov 2021 20:24

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