Formation of a Kinked Alignment of Solar Active Regions

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Abstract
Images of the solar corona as observed by the soft X-ray telescope aboard the Yohkoh satellite sometimes show a sequence of S-shaped active regions in the low latitudes of the northern or southern hemisphere. We suggest that the genesis of such a global structure is the emergence of a large-scale twisted magnetic flux tube embedded in the convection zone. When the magnetic twist exceeds a threshold value, the flux tube deforms itself into a helical structure through the kink instability. We present first results from a nonlinear three-dimensional magnetohydrodynamic (MHD) simulations of a twisted flux tube initially located in a gravitationally stratified, convectively unstable atmosphere. The effects of gravity, buoyancy, and the layered structure of the solar atmosphere (convection zone, cool photosphere/chromosphere, and hot corona) are taken into account. As the instability develops, the top portions of the helical structure rise by buoyancy and finally emerge into the corona, forming a sequence of strongly sheared magnetic loops. Intense vertical magnetic fields corresponding to sunspots are created at the footpoints of these coronal magnetic loops.