Flows along penumbral flux tubes in sunspots

Free access article

Issue		A&A Volume 440, Number 2, September III 2005


Page(s)		L29 - L32
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:200500155

A&A 440, L29-L32 (2005)
DOI: 10.1051/0004-6361:200500155

Letter

Instability of super-Alfvénic, serpentine solutions

J. H. Thomas

Department of Mechanical Engineering and Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627-0171, USA
e-mail: thomas@me.rochester.edu

(Received 9 May 2005 / Accepted 9 July 2005)

Abstract
The super-Alfvénic, undulating "sea-serpent" flow configurations along thin magnetic flux tubes, proposed by Schlichenmaier (2002, Astron. Nachr., 323, 303; 2003, ASP Conf. Ser., 286, 24) to explain both the Evershed flow and moving penumbral grains in a sunspot, are shown to be gravitationally unstable. Any undulations that occur for super-Alfvénic flow speeds will form preferentially in a horizontal plane and hence will not explain Evershed downflows or outward-moving penumbral grains. Sub-Alfvénic, arched flow configurations, on the other hand, are gravitationally stable.

Key words: sunspots -- Sun: magnetic fields -- magnetohydrodynamics (MHD)

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