With the ultimate goal of analysing the tropical climate sensitivity and the associated feedbacks in a Hadley circulation model, a representation for deep cumulus convection has been developed. The important features of this formulation are the maintenance of water vapor predictability, the calculation of precipitation efficiencies, and the hypothesis that cumulus buoyancy is ultimately maintained by solar radiation. On the grounds of dimensional analyses, bulk drafts are dependent on the depth of the troposphere and on the cumulus buoyancy fluxes -- effectively accomplishing the cleavage of the cumulus drafts from the mean ascending motion of the Hadley cell. Latent heat effects are implicitly accounted for through an empirical coefficient that scales the bulk drafts to observed magnitudes. The parameterization is activated when conditionally unstable stratification occurs within a chosen column depth. To determine the subgrid fluxes, the top-hat method is employed. Furthermore, the calculation of the fractional area covered by deep cumulus in the grid box is based on a time-scale representing the life cycle for deep clouds, on the amount of moisture needed to create the cumulus in the pre-determined depth, and on the water vapor made available from the explicit sources (advection and surface evaporation). In contradistinction to the procedure commonly used in mass flux schemes, the tuning is directly done on the precipitation flux reaching the ground. Comparisons of the calculated precipitation efficiencies with published observed data show a reasonable agreement.
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12th Conference on Atmospheric and Oceanic Fluid Dynamics