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T. Emonet (The University of Chicago), F. Moreno-Insertis (Instituto de Astrofisica de Canarias, Spain), M.P. Rast (High Altitude Observatory, NCAR)
When the Reynolds number is not small, the wake trailing a buoyant magnetic flux tube sheds vortex rolls therefore producing a Von Karman vortex street and an imbalance of vorticity in the tube which results in a transverse oscillation of the tube as a whole. The actual path followed by the magnetic structure is therefore directly affected by the amount of vorticity being produced in its boundary. Analytical expressions for the magnetic generation and viscous dissipation of vorticity in the boundary layer of buoyant magnetic flux tubes are obtained. Corresponding scaling laws are deduced and checked using a full compressible 2D MHD code. Interestingly, the observed trajectories can be satisfactorily reproduced by a simple analytical equation (which includes buoyancy, drag and vortex forces). I will conclude with some comparisons with classical results from the hydrodynamical literature (Strouhal number), and some comments about the rise time of buoyant magnetic structures through the solar convection zone.
The author(s) of this abstract have provided an email address for comments about the abstract: emonet@flash.uchicago.edu