From its source at the base of the convection zone magnetic flux is believed to rise buoyantly to the solar surface in the form of isolated tubes. As it rises, the cross section of such a tube will be distorted through its interaction with the surrounding unmagnetized medium. This distortion greatly affects its rate of rise and can ultimately lead to its fragmentation into two parallel tubes. We derive a set of Boussinesq fluid equations for studying the perpendicular dynamics of a rising flux tube. Integrating these numerically shows the tube distorting and then separating into two fragments with opposing senses of fluid circulation. The same behavior was observed in numerical simulations by Schuessler (1979). These counter-rotating elements move apart horizontally from each other and eventually stop rising. A simple picture of isolated buoyant material explains this result and confirms that the rise of the flux is prevented by its fragmentation. This has important consequences for theories of magnetic flux tube emergence.
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