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Astron. Astrophys. 338, 329-339 (1998)

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Numerical 3D simulations of buoyant magnetic flux tubes

S.B.F. Dorch and Å. Nordlund

The Niels Bohr Institute for Astronomy, Physics and Geophysics, Juliane Maries Vej 30, DK-2100 Copenhagen O, Denmark (dorch@astro.ku.dk; aake@astro.ku.dk)

Received 25 July 1996 / Accepted 1 July 1998


We have examined instabilities of non-thin buoyant magnetic flux tubes ascending through a solar convection zone model using numerical 3D MHD experiments. The experiments show that the fate of the flux tubes is entirely dependent on the internal topology of the magnetic field lines in the flux tube; if the initial topology is too simple the tube is quickly disrupted by a Rayleigh-Taylor like instability. The disruption is prevented or delayed if the field has a component that makes the topology non-trivial. Even a weak random or twisting component, an order of magnitude weaker than the longitudinal magnetic field, is sufficient to let the tube ascend as a more or less coherent structure. These 3D results may resolve the apparent contradiction between the success of experiments using the thin flux tube approximation to study the buoyant rise of magnetic flux tubes, and the rapid break-up of flux tubes found in 2D experiments.

Key words: Sun: activity – sunspots – Sun: magnetic fields instabilities – MHD

Send offprint requests to: S.B.F. Dorch

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© European Southern Observatory (ESO) 1998

Online publication: September 8, 1998