On the radiative processes associated with the tropical mesoscale convective systems

Tropical mesoscale convective systems (MCSs) are known to exert a large influence the radiative budget/heating profile of the tropical atmosphere through the mutual interactions between radiation and cloud hydrometeor fields. Once this cloud-induced radiative heat source is formed, it may act to modify the air motion and the latent energy budget within the cloud cluster, which may lead to changes in the characteristics of these tropical MCSs and their surrounding environments. A detail study on the radiative processes associated with the tropical MCSs is undertaken to address the radiative effects of these tropical cloud clusters on both the environment and the evolution of the tropical MCSs.; Numerical cloud modelings of two tropical MCSs are performed to obtain microphysical and thermodynamical information for the radiative transfer model. The results of radiation calculations indicate that the presence of tropical MCSs can significantly perturb the total (infrared plus solar) radiative budget and total radiative heating profile of the tropical atmosphere. Relative to the clear sky, these tropical MCSs represent an effective radiative heat source for the tropical atmosphere. Furthermore, the magnitude of these radiative effects on the environment increases as the cloud clusters mature.; Sensitivity experiments using the numerical cloud model are used to examine the effects of cloud radiative heat source on the evolution of the tropical MCSs. These experiments indicate that the feedback between these two is a function of the background environments (i.e., vertical shear profile and low level stability) in which these tropical MCSs are embedded. Furthermore, infrared radiative coolings at night can also play a role in aiding this feedback by destabilizing the lower levels of the atmosphere. A refined theory based on differential radiative heating between the cloudy regions and their surrounding clear skies (i.e., Gray and Jacobson, 1977) is used to explain these model behaviors. Under a typical tropical atmosphere characterized by a weak vertical shear profile, this cloud radiative feedback can have important consequences in (1) the energy and water budget of the tropical atmosphere, (2) the diurnal variations of the tropical convections, and (3) the equilibrium regional climate in the tropic.