Mesoscale convection at Prandtl numbers as low as 0.001*

Many natural convection flows possess regular patterns at an intermediate range of scales, the mesoscale range. A prominent example is granulation and supergranulation on the surface of the Sun. Here, we study mesoscale convection in the simpler Rayleigh-Bénard setup. Our direct numerical simulation studies are taken to Prandtl numbers as low as 0.001, which is beyond the capabilities of controlled laboratory experiments. We study several properties of the flow. The data show, for example, that the turbulence in the bulk of the convection layer is close to the classical homogeneous and istropic turbulence.