Abstract
A bulk diagnostic model is presented for the evaluation of the mass and heat fluxes due to convective ensembles. The cloud model is consistent with the hot-tower hypothesis and includes a moist downdraft, the depth and intensity of which are explicitly determined. The model is applied to the composite wave data of Reed and Recker (1971) and the sensitivity of convective mass fluxes and eddy heating rates to the assumed radiative cooling rate profile is examined.
The results obtained from the model using a radiative heating profile typical of clear “undisturbed” tropical regions were compared with those obtained using a radiative heating profile taken to be typical of disturbed conditions. Under such conditions, a thick cirrus shield is usually present. The model results show that the mass flux profile has a pronounced bimodal character regardless of the radiative heating rate profile (QR) employed. However, other characteristics of modeled convective ensembles are sensitive to the choice of QR. Specifically, under disturbed conditions, the model responds by increasing the deep convective mass flux while reducing shallow convective activity relative to the undisturbed state. The importance of the downdraft in terms of mass fluxes and eddy heat fluxes is enhanced under these disturbed conditions and the model results suggest that downdrafts originate in the upper troposphere. The level of maximum entrainment to the downdraft in the upper troposphere is further shown to be sensitive to the choice of the radiation heating profile.
