Vortices, shocks, and heating in the solar photosphere: effect of a magnetic field

Aims. We study the differences between non-magnetic and magnetic regions in the flow and thermal structure of the upper solar photosphere. Methods. Radiative MHD simulations representing a quiet region and a plage region, respectively, which extend into the layers around the temperature minimum, are analyzed. Results. The flow structure in the upper photospheric layers of the two simulations is considerably different: the non-magnetic simulation is dominated by a pattern of moving shock fronts while the magnetic simulation shows vertically extended vortices associated with magnetic flux concentrations. Both kinds of structures induce substantial local heating. The resulting average temperature profiles are characterized by a steep rise above the temperature minimum due to shock heating in the non-magnetic case and by a flat photospheric temperature gradient mainly caused by Ohmic dissipation in the magnetic run. Conclusions. Shocks in the quiet Sun and vortices in the strongly magnetized regions represent the dominant flow structures in the layers around the temperature minimum. They are closely connected with dissipation processes providing localized heating.