Three-dimensional MHD simulations of the emergence of twisted flux tubes Original Research Article

We carried out three-dimensional magnetohydrodynamic (MHD) simulations of the emergence of a twisted magnetic flux tube initially imbedded 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. For sufficiently long wavelength perturbations (λp > 10 H, where H is the local scale height), the flux tube also subjects to the undular mode of the magnetic buoyancy instability (Parker instability). The emergent portions of such helically deformed, undulating flux tube show a series of S-shaped X-ray emitting regions as observed by the Yohkoh satellite.