Favier, B., Louve, L., Edmunds, L. J., Silvers, L. J. & Proctor, M. R. E. (2012). How can largescale twisted magnetic structures naturally emerge from buoyancy instabilities?. Monthly Notices of the Royal Astronomical Society, 426(4), pp. 33493359. doi: 10.1111/j.13652966.2012.21920.x

PDF
Download (2MB)  Preview 
Abstract
We consider the threedimensional instability of a layer of horizontal magnetic field in a polytropic atmosphere where, contrary to previous studies, the field lines in the initial state are not unidirectional. We show that if the twist is initially concentrated inside the unstable layer, the modifications of the instability reported by several authors (see e.g. Cattaneo et al. (1990)) are only observed when the calculation is restricted to two dimensions. In three dimensions, the usual interchange instability occurs, in the direction fixed by the field lines at the interface between the layer and the fieldfree region. We therefore introduce a new configuration: the instability now develops in a weakly magnetised atmosphere where the direction of the field can vary with respect to the direction of the strong unstable field below, the twist being now concentrated at the upper interface. Both linear stability analysis and nonlinear direct numerical simulations are used to study this configuration. We show that from the smallscale interchange instability, largescale twisted coherent magnetic structures are spontaneously formed, with possible implications to the formation of active regions from a deepseated solar magnetic field.
Item Type:  Article 

Subjects:  Q Science > QB Astronomy 
Divisions:  School of Engineering & Mathematical Sciences > Department of Mathematical Science 
URI:  http://openaccess.city.ac.uk/id/eprint/1398 
Actions (login required)
View Item 
Downloads
Downloads per month over past year