Non-Boussinesq convection at low Prandtl numbers relevant to the Sun

The figures on the left show effect of Prandtl number (Pr) Rayleigh-B\'enard problem with Boussinesq conditions, for same Grashof ${10}^{9}$. Top: Pr = 12.73; bottom, ${10}^{\ensuremath{-}4}$. plot right shows that low molecular yields an inversely varying turbulent number; is, flow behaves effectively as a high fluid. data are non-Boussinesq conditions. qualitative is case well, but dependence has weaker power law exponent about $\ensuremath{-}1/3$.