Letter to the Editor
Flows along penumbral flux tubes in sunspots
Instability of super-Alfvénic, serpentine solutions
Department of Mechanical Engineering and Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627-0171, USA e-mail: firstname.lastname@example.org
Accepted: 9 July 2005
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)
© ESO, 2005