Steady convection in deep compressible layers (Q1976347)

It is known from the literature that the standard mixing-length model of convection traditionally used in astrophysics is based on an analogy with the kinetic theory of gases. Simulations of steady convection do not find eddies of order of local scale height, but rather single cells extending over several scale heights from top to bottom of the layer. Simulations of turbulent convection with various sub-grid scale closures give plumes or downdrafts extending over several scale heights. Here the author presents a simple explanation of these results. Namely, it is shown that the turn-over time of convection is small compare to the thermal relaxation time, so the convection is a global phenomenon, the whole layer adjusting to a global equilibrium. In steady convection single eddies span the layer, in turbulent convection plumes or downdrafts extend over several scale heights.