EXCITATION OF NONLINEAR MHD WAVES BY FOOT-POINT MOTIONS

Numerical simulations are performed to investigate the excitation of m agnetohydrodynamic waves in coronal loops by photospheric shearing mot ions. In the simulations the solar coronal loop is modelled as a strai ght slab of enhanced gas density. The plasma is described by magnetohy drodynamic equations that include finite gas pressure effects and magn etic diffusivity. The Alfven wave is artificially suppressed from the system. MHD waves are excited by imposing oscillations at one end of t he plasma slab. A plasma responds to a foot-point motion by kink or sa usage waves in dependence on the polarization of a driver. The foot-po int motion induces a growth in the parallel velocity. The growth occur s in a resonant layer on a time scale which is much less than a typica l life time of a loop. The heating associated with the resonant absorp tion of the waves is very small and can thus not be considered as rele vant for the coronal heating mechanism. The nonlinearity of the MHD eq uations gives rise to a distorted plasma flow, introducing an asymmetr y in the system, and speeds up the occurrence of the resonant layer.