Twisted Ux Tubes and How They Get That Way 1. Flux Tubes

According to present theories, the Sun's magnetic eld rises through the convection zone in the form of slender strands known as ux tubes, traditionally studied using \thin ux tube" models. While these models have been remarkably successful they have only recently begun to account for tubes with twisted magnetic ux, in spite of observational evidence for such twist. In this work we review the recent developments pertaining to twisted magnetic ux tubes and compare quantitative predictions to observations. Hydrodynamic theory predicts a role for twist in preventing fragmentation. Excessive twist can also lead to magnetohydrodynamic instability aaecting the dynamics of the tube's axis. A thin tube model for a twisted tube suggests several possibilities for the origin of twist. The most successful of these is the-eeect whereby twist arises from deformation of the tube's axis by turbulence. Simulations show that the-eeect agrees with observations in magnitude as well as latitudinal dependence. Magnetic eld appears at the solar surface in the form of isolated domains comprising active regions (ARs). These have been understood as the manifestation of slender, pressure-connned strands of magnetic eld called ux tubes (Parker 1955a). Flux tubes rise buoyantly as arched-loops, originating at the base of the convection zone (CZ) where they are generated by dynamo action. Equations describing the dynamical evolution of a buoyant ux tube were proposed by Spruit 1981] and have been employed in modiied form Numerical solutions of such model equations have shown good quantitative agreement with sunspot data. This agreement includes the measured \tilt angle" of a