Enhancement of Photospheric Meridional Flow by Reconnection Processes

Abstract

We simulate the two-dimensional transport of the open magnetic flux on the surface of the Sun. The temporal evolution of the flux density depends on the advective motions due to solar differential rotation and poleward meridional flow and on an effective spatial diffusive motion. The latter is a result of the uniform diffusion of field line footpoints in the network lanes and a nonuniform diffusion offield lines due to reconnection of open field lines with closed loops on the solar surface. The gradient of the diffusion coefficient represents an effective velocity in addition to the advective velocity. We investigate the behavior of the steady state solution for solar minimum and solar maximum conditions with spatially uniform and nonuniform diffusion coefficients. We find that for solar minimum conditions, the effect of spatial diffusion resulting from reconnection processes enhances the poleward meridional flow due to the large-scale preferred direction in the gradient of the diffusion coefficient. For solar maximumconditions,theneteffectofspatialdiffusionisminimalbecauseoftheisotropicandlocalgradientsofthe diffusion coefficient. Our simulation demonstrates that magnetic reconnection processes on the solar surface can be a mechanism to vary motions on the photosphere, in particular, poleward meridional flow.