ALFVÉN WAVES IN SIMULATIONS OF SOLAR PHOTOSPHERIC VORTICES

Abstract

Using advanced numerical magneto-hydrodynamic simulations of the magnetised\nsolar photosphere, including non-grey radiative transport and a non-ideal\nequation of state, we analyse plasma motions in photospheric magnetic vortices.\nWe demonstrate that apparent vortex-like motions in photospheric magnetic field\nconcentrations do not exhibit "tornado"-like behaviour or a "bath-tub" effect.\nWhile at each time instance the velocity field lines in the upper layers of the\nsolar photosphere show swirls, the test particles moving with the\ntime-dependent velocity field do not demonstrate such structures. Instead, they\nmove in a wave-like fashion with rapidly changing and oscillating velocity\nfield, determined mainly by magnetic tension in the magnetised intergranular\ndownflows. Using time-distance diagrams, we identify horizontal motions in the\nmagnetic flux tubes as torsional Alfv\\'en perturbations propagating along the\nnearly vertical magnetic field lines with local Alfv\\'en speed.\n