Numerical study of convective scale selection in a cloud-topped marine boundary layer

The conditions for the generation of broad convection cells in a cloud-topped, convective, marine atmospheric boundary layer are studied with an idealized two-dimensional model of non-precipitating moist convection. The inversion layer is represented by an elastic upper boundary rather than by the rigid lid that is often employed in these sorts of studies. A necessary condition for the formation of broad cells in the model is that either the convection penetrates the inversion by a distance at least half the average depth of the convecting atmospheric boundary layer, or that the rate of entrainment of dry inversion air is substantially reduced above cloud tops. The penetrative solutions display some similarity with mesoscale cellular convection observed during KONTUR, while the non-penetrative solutions display some similarity with AMTEX observations.