NUMERICAL SIMULATIONS OF MHD WAVE EXCITATION IN BOUNDED PLASMA SLABS

Numerical simulations are performed in the framework of nonlinear resi stive 2.5-dimensional magnetohydrodynamics to investigate the response of a coronal loop to shearing motions of the footpoints. A simple sla b plasma with straight magnetic field lines is used to model the coron al loop, with the photospheric ends represented by impermeable walls. The hot, dense loop plasma is approximated by smoothed step-function p rofiles. The results show that an initially excited Alfven wave reveal s a 1/x-type singularity, which is characteristic of the linear Alfven resonances, smoothed by the resistive dissipation. Both fast and slow magnetosonic waves are driven by the nonlinear Alfven wave. The slow magnetosonic waves concentrate their energies in resonance layers, and their associated flows exhibit singularities of the 1/x-type. Alfven resonances, which are absent from the system in the case of linear wav es, develop late in time as the Alfven-wave amplitude grows into the n onlinear regime, and their development is accelerated for larger-ampli tude driving forces. The resultant heating associated with the resonan ces and phase mixing of the waves is concentrated in the region of lar ge Alfven-speed gradients.