The numerical simulation of MHD wave modes excited by photospheric motions and their energy fluxes. (Invited)

Abstract:

The ground- and space-based solar observations reveal the presence of small-scale plasma motion between convection cells in the solar photosphere. These motions in intergranular magnetic field concentrations are responsible for the generation of different types of MHD wave modes, for example, kink, sausage and torsional Alfven waves. In this study we will show the results of a 3D numerical simulation of the excitation and propagation of these MHD modes in the realistic magnetic configurations mimicking the photospheric magnetic flux tubes. Based on a self-similar approach the magnetic flux tube configurations were constructed and implemented in the VALIIIC model of the solar atmosphere. A novel method for decomposing the velocity perturbations into parallel, perpendicular, and azimuthal components in a 3D geometry was developed using field lines to trace a volume of constant energy flux. This method was used to identify the excited wave modes propagating upwards from the photosphere and to compute the percentage of energy contributed by each mode. We have found that for all cases where torsional motion is present the main contribution to the flux (60%) was the Alfven wave. A vertical driver was found to excite mainly the fast- and slow-sausage modes whilst a horizontal driver primarily excited the slow kink mode.