Mon. Not. R. Astron. Soc.
314 (2000) 793-806.
doi:10.1046/j.1365-8711.2000.03407.x
Development of structure in pores and sunspots:
flows around axisymmetric magnetic flux tubes
N.E. Hurlburt(1) and
A.M.Rucklidge(2)
(1) Lockheed Martin Solar and Astrophysics Laboratory,
Organization L9-41 Building 252, Palo Alto, CA 94304, USA
(2) Department of Applied Mathematics and Theoretical Physics,
University of Cambridge, Cambridge, CB3 9EW, UK
Abstract.
Flux elements, pores and sunspots form a family of magnetic features
observed at the solar surface. As a first step towards developing a fully
nonlinear model of the structure of these features and of the dynamics of their
interaction with solar convection, we conduct numerical experiments on
idealised axisymmetric flux tubes in a compressible convecting atmosphere in
cylindrical boxes of radius up to eight times their depth. We find that the
magnetic field strength of the flux tubes is roughly independent of both
distance from the centre and the total flux content of the flux tube, but that
the angle of inclination from the vertical of the field at the edge of the tube
increases with flux content. In all our calculations, fluid motion converges on
the flux tube at the surface. The results compare favourably with observations
of pores; in contrast, large sunspots lie at the centre of an out-flowing moat
cell. We conjecture that there is an inflow hidden beneath the penumbrae of
large spots, and that this inflow is responsible for the remarkable longevity
of such features.
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