“Triggering” – Scheme in Climate Model Produces Improved Weather Prediction


Climate simulations performed with general circulation models (GCMs) are widely viewed as the principal scientific basis for developing policies to address potential future global climate scenarios, e.g. global warming, ozone depletion, changes in land use, etc. The Climate Change Prediction Program-Atmospheric Radiation Program Parameterization Testbed (CAPT) , is aimed at enhancing model performance through a numerical weather prediction methodology. The CAPT effort takes the novel approach of running a climate model in weather mode. Thus CAPT (i) diagnoses details of model systematic errors by comparing GCM simulations with available observations; and (ii) reduces these systematic errors by improving the representation of key processes, and thereby increase the accuracy of GCM simulations. Publications describe the use of the CAPT framework to identify parameterization deficiencies in the Community Atmosphere Model, or CAM2, the atmospheric component of the Community Climate System Model. CAM2 simulations produced too frequent convective precipitation (rain) during the day in summertime; much more than actually occurred. Researchers introduced a modified convective initialization – or “triggering” – scheme that produced fewer, more intense rain events. The resulting model (CAM2M) showed a significant reduction in convective events and much better agreement with ARM and satellite observations of rainfall.