Submitted to Geophys. Astrophys. Fluid Dynamics (2011)
Formation of magnetic flux tubes in cylindrical wedge geometry
G.J.J. Botha(1),
A.M.Rucklidge(2) and
N.E. Hurlburt(3)
(1) Department of Physics,
University of Warwick, Coventry CV4 7AL, UK
(2) Department of Applied Mathematics,
University of Leeds, Leeds LS2 9JT, UK
(3) Lockheed Martin Solar and Astrophysics Laboratory,
Organization L9-41 Building 252, Palo Alto, CA 94304, USA
Abstract.
Three-dimensional (3D) magnetohydrodynamic (MHD) numerical simulations have not
been able to demonstrate convincingly the spontaneous formation of large
vertical, i.e., pore-like or sunspot-like, flux tubes. Two-dimensional (2D)
magnetoconvection in axisymmetric cylinders forms a central magnetic flux tube
surrounded by annular convection rings. To study the robustness of this type of
solution in three dimensions, the nonlinear resistive MHD equations are solved
numerically in a 3D cylindrical wedge from an initially uniform vertical
magnetic field. It is shown that the 2D result is retrieved for small domain
radii. However, for larger radii the central axis loses its importance and in
this case many convection cells form in the numerical domain. Magnetic flux is
captured between cells where flow converges and the reduced amount of flux that
congregates at the central axis is eroded by the surrounding convection.
preprint version of this paper (11.6MB)