Single-column and cloud ensemble model simulations of TOGA-COARE convective systems

A prognostic cloud prediction scheme, designed for large-scale models, has been incorporated into a Single Column Model (SCM) and used to simulate the cloud cluster properties observed during the 19-26 December, 1992 Tropical Oceans Global Atmosphere (TOGA)-Coupled Ocean Atmosphere Response Experiment (COARE). Results from the SCM simulations have been compared with simulated profiles obtained from the Goddard Cumulus Ensemble Model (GCEM). Observed large-scale advective temperature, water vapor, and surface fluxes have been used as forcings to run the SCM and the GCEM. Results indicate that the SCM produces mixed profiles of cooling/warming and drying/moistening in the vertical, which are highly sensitive to the prescribed surface fluxes. Errors in the temperature and moisture profiles simulated by the SCM are about +/-3 K and +/-3 g kg(-1), while those from the GCEM are approximately -2 K and 1 g kg(-1) at most levels. The SCM produced -10 % errors in the relative humidity above 700 mb and -30 % at the surface, while in the GCEM, the errors were about 10 to 15 % at most levels. The distributions of precipitation rates are fairly well simulated, but the high cloud fractions are slightly underestimated by the SCM as compared to the GCEM. The cloud liquid water is underestimated, but the ice contents are slightly overestimated by the SCM. Results show that the SCM has been able to simulate the distributions of temperature, moisture, and precipitation rates fairly well as compared to the GCEM and other GEWEX Cloud System Study (GCSS) model intercomparison products. Sensitivity studies have been carried out to investigate the implications of different physical processes in the SCM. Results indicate that the interactions between various physical processes are nonlinear, and a mere substitution of the heating and moistening profiles from the GCEM may not be able to reproduce the observed temperature and moisture values by the SCM. The SCM has also been used to simulate the distributions of large-scale cloud cluster properties and their diurnal variation during the disturbed and suppressed periods of convection. Results show that the diurnal variations of simulated values are in agreement with many observational studies conducted by different authors over the TOGA-COARE.