The organization of moist convection by internal gravity waves

A two-dimensional, Boussinesq approximated model is used to investigate the grouping of moist convection and its connection with internal gravity waves. The effect of moisture has been taken into account as a flow-dependent heating. The model sensitivity to parameters has been studied systematically. Numerical simulations are started from a state of rest with a conditionally unstable stratification. Distinct individual convective cells appear soon after small random perturbations are introduced. These cells later become organized into groups, as the equilibrium state of the model is approached asymptotically in the form of an oscillation. The oscillation of the condensational heating generates gravity waves, which are embedded in the subsidence of the convective cells and thus propagate in a stably stratified environment. The gravity waves modulate the generation of new convective cells which in turn introduce new heat sources, giving rise to additional gravity waves, and so on. If the lapse rate of the reference temperature profile is unstable, the oscillation of the condensational heating will persist for a long time and more updrafts will appear. If the dissipation is weak, the waves can propagate a long distance without being significantly damped. In these situations, strong nonlinear interactions between waves and moist updrafts are possible which leads to the grouping of convective clouds.