[Previous] | [Session 3] | [Next]
Y. Fan (HAO, NCAR)
Bipolar magnetic regions on the solar surface are believed to correspond to the topmost portions of \Omega-shaped arching flux tubes that have risen buoyantly from the base of the solar convection zone, where strong toroidal magnetic fields are being generated by the dynamo process. The dynamic evolution of such rising flux tube structures in the solar convection zone has been studied extensively using a simplified thin flux tube model, and more recently with direct multi-dimensional MHD simulations. In this talk I will give an overview of some recent results of 3-dimensional MHD simulations of the formation and dynamic rise of buoyant \Omega loops in the solar interior: (1) I will present direct numerical simulations of the formation of coherent, 3-D \Omega-loop structures as a result of the growth of the undular Parker instability of a neutrally buoyant horizontal flux tube or flux sheet initially in hydrostatic equilibrium. (2) The question of the critical twist necessary for maintaining cohesion of the rising flux tubes will be discussed in light of recent 3-D simulations of fragmenting \Omega-loops by Abbett et al. (3) I will describe simulations of the non-linear growth of the current driven kink instability along rising flux tubes that are highly twisted, and show that kinked \Omega-loops reproduce several observed features of the so-called \delta-sunspots. Finally, the issue of the connectivity of the emerged flux with its source at the base of the convection zone will be discussed by examining the conditions of hydrostatic equilibrium along a vertical flux tube extending across the solar convection zone.
The National Center for Atmospheric Research (NCAR) is sponsored by the National Science Foundation