Large-scale forcing and cloud-radiation interaction in the tropical deep convective regime

The simulations of tropical convection and thermodynamic states in response to different imposed large-scale forcing are carried out by using a cloud- resolving model and are evaluated with the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment observation. The model is for ced either with imposed large-scale vertical velocity and horizontal temper ature and moisture advections (model I) or with imposed total temperature a nd moisture advections (model 2). The comparison of simulations with observ ations shows that bias in temperature and moisture simulations by model 1 i s smaller than that by model 2. This indicates that the adjustment of the m ean thermodynamic stability distribution by vertical advection in model 1 i s responsible for better simulations. Model 1 is used to examine effects of different parameterized solar radiati ve and cloud microphysical processes. A revised parameterization scheme for cloud single scattering properties in solar radiation calculations is foun d to generate more solar heating in the upper troposphere and less heating in the middle and lower troposphere. The change in the vertical heating dis tribution is suggested to stabilize the environment and to cause less strat iform cloud that further induces stabilization through cloud-IR interaction . The revised scheme also causes a drier middle and lower troposphere by we akening vertical moisture flux convergence. Also tested is the effect of a revised parameterization scheme for cloud microphysical processes that tend s to generate more ice clouds. The cloud-induced thermal effect in which le ss ice cloud leads to less infrared cooling at cloud top and more heating b elow cloud top is similar to the effect of no cloud-radiation interaction s hown in a sensitivity experiment. However. the exclusion of cloud-radiation interaction causes drying by enhancing condensation, and the reduction of ice clouds by the microphysics scheme induces moistening by suppressing con densation.