Mathematics – Logic
Scientific paper
Jun 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006spd....37.0703c&link_type=abstract
American Astronomical Society, SPD meeting #37, #7.03; Bulletin of the American Astronomical Society, Vol. 38, p.228
Mathematics
Logic
1
Scientific paper
We consider the plasma and magnetic field dynamics of a vertical flux rope located below the photosphere that is subjected to footpoint twisting at the base of the flux rope. Such a structure may constitute the idealized subphotospheric extension of a leg of a coronal flux rope. We use a straight cylinder having both poloidal (locally azimuthal) and toroidal (locally axial) magnetic field components. The structure is initially in equilibrium with the ambient pressure. The equilibrium and MHD stability properties of a range of magnetic field profiles are studied. We also consider the well-known Gold and Hoyle model. We increase the poloidal magnetic flux by subjecting the magnetic footpoints of the initial flux rope to a twisting motion at the base of the simulation region. The resulting dynamics are investigated using a fully three dimensional (3-D) MHD model. First, we find that the poloidal magnetic field in the high-beta plasma outside the current channel becomes strongly incoherent while the toroidal magnetic field in the current channel itself with relatively low beta can better maintain its geometrical integrity. At any point in space, the degree of incoherence increases with the depth of the source of the twisting motion. Second, as the field becomes more incoherent and complex around the flux rope, magnetic reconnection can occur, allowing material to be decoupled from the flux rope and its poloidal field, which topologically is the horizontal component outside strong vertical field regions. We examine the flow field and magnetic field values on isodensity surfaces as a function of the depth of the footpoints and discuss the implications for potentially observable photospheric signatures.Work supported by ONR
Chen James
Huba Joseph D.
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