Evershed Flows along Penumbral Flux Tubes in Sunspots
Abstract
Theoretical models of the Evershed flow in a sunspot based on the thin flux tube approximation are compared. The super-Alfvénic, ``sea-serpent'' flow configurations found by Schlichenmaier (2002, 2003) are shown to be gravitationally unstable. If indeed super-Alfvénic flow speeds can be achieved along penumbral flux tubes, any undulations that occur will form preferentially in a horizontal plane and hence will not explain the observed Evershed downflows or outward-moving penumbral grains. On the other hand, sub-Alfvénic, arched flow configurations, such as the siphon-flow models of Montesinos and Thomas (1997), are gravitationally stable. The outer part of a siphon-flow flux tube is submerged, in opposition to its magnetic buoyancy, by downward magnetic flux pumping in the granular convective layer outside the sunspot.
- Publication:
-
Solar MHD Theory and Observations: A High Spatial Resolution Perspective
- Pub Date:
- December 2006
- Bibcode:
- 2006ASPC..354..224T