Dynamics of Magnetic Flux Tubes

The magnetic fields of the Sun are known to drive a myriad of phenomena from sunspots to solar flares. Sunspots are among the most prominently visible surface magnetic features. They are known to be produced by magnetic flux tubes that emerge through the surface. The progenitors of all magnetic features - the magnetic flux tubes - are commonly accepted to be the product of the dynamo action that is believed to operate in the deep interior of the Sun at a depth of roughly 200,000 km. The study of the dynamics of sunspots has attracted a large number of investigators. However, we have yet to reach a complete understanding of their origin, formation, morphology and dynamics.

To understand the morphology and dynamics of sunspots we studied the dynamics of their progenitors. Magnetic flux tubes have to traverse a highly turbulent convectively unstable region before they can produce the sunspots at the surface. We modeled the flux tube to be a one-dimensional string with all properties of a magnetic flux tube allowed to move in the three-dimensional space of the convection zone. We could successfully explain a number of dynamical and morphological properties of sunspots.

Most importantly, to explain these surface properties of sunspots we found that the magnetic field strength had to be 100,000 G at the base of the convection zone. This is an order of magnitude larger than the magnetic field strength that can be in energy equipartition with the turbulent motions.