Kinematic Modeling of Vortices in the Solar Photosphere

The application of local correlation tracking to the proper motions of granules yields the horizontal velocity field at the solar surface. The divergence of the velocity reveals a pattern of sources and sinks. The vorticity is concentrated at sinks to form local swirls (with either sense of motion). A simple kinematic model of such a vortex, in which the radial inflow is balanced by an eddy viscosity, predicts that the vorticity should have a Gaussian profile. This prediction is confirmed by comparison with three sets of high-resolution observations, obtained from Spacelab 2 and from the Swedish Vacuum Solar Telescope on La Palma. Finally, we develop a more precise version of the model and provide an estimate of the eddy viscosity due to small-scale granulation.