THE NONLINEAR MHD EVOLUTION OF AXISYMMETRICAL LINE-TIED LOOPS IN THE SOLAR CORONA

The nonlinear evolution of the m = 0 sausage mode in coronal loops (Go ld and Hoyle 1960 Mon. Not. R. Astron. Sec. 120 89) is investigated us ing numerical simulations. For the ideal line-tied case the growth rat e of the linear phase of the instability is successfully reproduced, a nd it is found that the nonlinear development leads to the formation o f a new equilibrium with an embedded, curved, current concentration (n ot, however, a current sheet). This new equilibrium is not symmetric a bout the centre of the loop. For periodic boundary conditions a simila r evolution is found, but with the final equilibrium bring symmetric i n which a straight, radial current concentration (possibly a current s heet) is embedded. In the line-tied resistive case the field lines rec onnect, leading to the ejection of a plasmoid and relaxation to a (dif ferent) equilibrium.