Mesogranulation and small-scale dynamo action in the quiet Sun

Context. Regions of quiet Sun generally exhibit a complex distribution of small-scale magnetic field structures, which interact with the near-surface turbulent convective motions. Furthermore, it is probable that some of these magnetic fields are generated locally by a convective dynamo mechanism. In addition to the well-known granular and supergranular convective scales, various observations have indicated that there is an intermediate scale of convection, known as mesogranulation, with vertical magnetic flux concentrations accumulating preferentially at the boundaries of mesogranules. Aims. Our aim is to investigate the small-scale dynamo properties of a convective flow that exhibits both granulation and mesogranu-lation, comparing our findings with solar observations. Methods. Adopting an idealised model for a localised region of quiet Sun, we use numerical simulations of compressible magnetohy-drodynamics, in a three-dimensional Cartesian domain, to investigate the parametric dependence of this system (focusing particularly upon the effects of varying the aspect ratio and the Reynolds number). Results. In purely hydrodynamic convection, we find that mesogranulation is a robust feature of this system provided that the domain is wide enough to accommodate these large-scale motions. The mesogranular peak in the kinetic energy spectrum is more pronounced in the higher Reynolds number simulations. We investigate the dynamo properties of this system in both the kinematic and the nonlin-ear regimes and we find that the dynamo is always more efficient in larger domains, when mesogranulation is present. Furthermore