NUMERICAL SIMULATIONS OF DRIVEN MHD WAVES IN CORONAL LOOPS

The solar corona, modeled by a low-beta, resistive plasma slab, sustai ns MHD wave propagations due to footpoint motions in the photosphere. Simple test cases are undertaken to verify the code. Uniform, smooth a nd steep density, magnetic profile and driver are considered. The nume rical simulations presented here focus on the evolution and properties of the Alfven, fast and slow waves in coronal loops. The plasma respo nds to the footpoint motion by kink or sausage waves dc, ending on the amount of shear in the magnetic field. The larger twist in the magnet ic field of the loop introduces more fast-wave trapping and destroys i nitially developed sausage-like wave modes. The transition from sausag e to kink waves does not depend much on the steep or smooth profile. T he slow waves develop more complex fine structures, thus accounting fo r several local extrema in the perturbed velocity profiles in the loop . Appearance of the remnants of the ideal singularities characteristic of ideal plasma is the prominent feature of this study. The Alfven wa ve which produces remnants of the ideal x(-1) singularity, reminiscent of Alfven resonance at the loop edges, becomes less pronounced for la rger twist. Larger shear in the magnetic field makes the development o f pseudo-singularity less prominent in case of a steep profile than th at in case of a smooth profile. The twist also causes heating at the e dges, associated with the resonance and the phase mixing of the Alfven and slow waves, to slowly shift to layers inside the slab correspondi ng to peaks in the magnetic field strength. In addition, increasing th e twist leads to a higher heating rate of the loop. Remnants of the id eal log \x\ singularity are observed for fast waves for larger twist. For slow waves they are absent when the plasma experiences large twist in a short time. The steep profiles do not favour the creation of pse udo-singularities as easily as in the smooth case.