The behaviour of a cloud ensemble in response to external forcings

The behaviour of a population of tropical moderate precipitating clouds is investigated with a cloud-resolving model over a period equivalent to 2-3 days. The response of the system is analysed as a function of external forcings, comprising shortwave and longwave radiation, large-scale ascent effects and surface fluxes. Radiative and large-scale ascent processes enhance the convective activity. In all the experiments, an accumulation of humidity is observed in the upper part of the cloud layer and in the region above. In the case of weak large-scale ascent, a diurnal cycle of convection is found, having maximum activity during the night and minimum activity around noon. Depending on the anvil cloud coverage, a modulation of this cycle is found whose cause can be explained through an infrared radiative feedback. The anvil deck also has a diurnal cycle but phase shifted by six hours with reference to the convective cycle.