Impact of the Chikira-Sugiyama Convection Scheme on the GFS.

Abstract:

As part of a Climate Process Team effort to implement a unifed representation of deep convection across horizontal model resolution in the EMC/NCEP Global Forecast System (GFS) we have installed a conventional version of the Chikira-Sugiyama convection scheme which will serve as the vehicle for the unified representation. This scheme is based on an entraining-plume model; the lateral entrainment rate vertically varies depending on buoyancy and updraft velocity; the updraft ensemble is spectrally represented with cloud types defined by updraft velocity at cloud base; the cloud base mass flux is prognostic according to the method of the prognostic Arakawa-Schubert scheme.

The operational GFS and the CS-GFS were configured to T126 horizontal resolution and each integrated 3 years with climatological SST and sea ice boundary conditions. Preliminary analysis indicates that the CS simulation was found to reduce surface and top of atmosphere imbalances in the total energy balances present in the control simulation. The CS simulation also increased, albeit excessively, the frequency distribution of intense precipitation rates and precipitatable water. Further differences in model mean state and variability will be analyzed and presented.