Thursday, 6 June 2002
Large-scale organization of tropical convection in idealized numerical simulations: Impact of radiative processes
This presentation will discuss numerical results pertinent to the problem of large-scale convection organization in the tropics. The problem spans a wide range of spatial and temporal scales and involves several physical processes, such as atmosphere-ocean interaction, moist convection, cloud microphysics, radiative transfer, and equatorial wave dynamics. Many theories have been proposed in the past to explain the observed large-scale convection organization (e.g., wave-CISK, WISHE, water vapor feedback, stochastic convective excitation, etc.). The paper will look at the role of radiative processes in this problem. First, 2D (x-z) cloud-resolving simulations will be presented in which a periodic global-scale horizontal domain is used (20,000 km) and a horizontally homogeneous SST is assumed. These idealized simulations are relevant to understanding the interaction between tropical convection and eastward-propagating Kelvin waves. Indeed, the spontaneous organization of convection into eastward-propagating super-cloud-clusters is observed in some of the 2D simulations. Second, the interaction between equatorially-trapped disturbances and tropical convection as simulated by a nonhydrostatic global model applying the cloud-resolving convection parameterization (CRCP, the super-parameterization) will be discussed. The CRCP represents subgrid scales of the global model by imbedding a 2D cloud-resolving model in each column of the global model. The modeling setup is a constant SST aquaplanet (with the size and rotation as Earth) in radiative-convective equilibrium. Spontaneous development of eastward-propagating equatorially-trapped MJO-like disturbances is observed in these simulations. The presentation will discuss results from the two sets of simulations with the emphasis on the interaction of radiation with water vapor and clouds.