J. Geophys. Res., submitted 11/12.
Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY.
Adam H. Sobel
Department of Applied Physics and Applied Mathematics, Department of Earth and Environmental Sciences, and Lamont-Doherty Earth Observatory, Columbia University, New York, NY.
Department of Earth and Planetary Sciences and School of Engineering and Applied Sciences, Harvard University, Cambridge, MA
Variations in deep convective activity during the 4-month TOGA-COARE field campaign are simulated using a cloud-resolving model (CRM). The model is driven by large-scale vertical velocities that are parameterized using one of two different methods: the damped gravity wave method and the weak temperature gradient (WTG) method. Observed temperature profiles are used in these methods as the reference against which temperature anomalies are computed; the parameterized large-scale vertical velocities are coupled to those temperature (or virtual temperature) anomalies. Sea surface temperature, radiative fluxes, and relaxation of the horizontal mean horizontal wind field are also imposed. Simulations with large-scale vertical velocity imposed from the observations are performed for reference. The primary finding is that the CRM with parameterized large-scale vertical motion can capture the intraseasonal variations in rainfall to some degree. Experiments in which one of several observation-derived forcings are set to their time mean value suggest that those which influence direct forcings on the moist static energy budget – surface wind speed and sea surface temperature (which together influence surface evaporation) and radiative cooling – play important roles in controlling convection, while the imposed temperature variations do not. The parameterized large scale vertical velocity has a vertical profile that is too bottom-heavy compared to observations when the wave coupling method is used with vertically uniform Rayleigh damping on horizontal wind, but is too top-heavy when the WTG method is used.