11th Conference on Atmospheric Radiation and the 11th Conference on Cloud Physics

Monday, 3 June 2002: 11:15 AM
Cloud microphysics and the tropical climate: Idealized aquaplanet simulations using the cloud-resolving convection parameterization (CRCP)
Wojciech W. Grabowski, NCAR, Boulder, CO
Poster PDF (2.0 MB)
The essence of tropical dynamics is a mutual interaction between moist convection and large--scale flow. The interaction involves dynamical, thermodynamical, radiative and surface processes acting on a wide range of spatial and temporal scales. It is often argued that the structure of the tropical atmosphere depends strongly on cloud microphysical processes because these processes play fundamental roles in the release of latent heat, formation of precipitation, and interactions between clouds and radiation. Because of the range of scales involved, this issue has been previously investigated using approaches with very simple representations of cloud dynamics and cloud microphysics. This paper will discuss links between cloud processes and the mean state of the tropical atmosphere in idealized aquaplanet simulations which apply the cloud-resolving convection parameterization (CRCP, the super-parameterization). CRCP represents the subgrid scales of the global model by embedding a 2D cloud-resolving model in each column of the global model. The cloud-resolving models are aligned along the east-west direction and allow for coupling of not only thermodynamic variables, but the zonal momentum as well. The modeling setup is a constant SST aquaplanet (with the size and rotation as Earth) in radiative-convective equilibrium. Spontaneous formation of coherent structures with deep convection on the leading edge and strong surface westerly winds to the west (the westerly wind bursts) is observed inside the equatorial waveguide. These coherent structures resemble the Madden-Julian Oscillations (MJO) observed in the terrestrial tropics and are present in simulations applying prescribed and interactive radiation, various orientation of CRCP domains (east-west versus north-south), and various horizontal resolutions of the global model. This presentation will focus on the sensitivity of these results to the representation of cloud microphysics in the 2D cloud-resolving models of CRCP.

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