The sensitivity of a LAM model to inclusion of cloud fraction in an explicit representation of convection

This study presents some results on the sensitivity of a regional model (LAHM/Geophysical Fluid Dynamics Laboratory, CIMA), to the inclusion of cloud fraction in an explicit representation of convection. To accomplish this objective, four different synoptic situations were selected, all of them associated with heavy precipitation over Argentina. Several experiments were carried out, one of them was with doubled vertical resolution. Precipitation fields obtained with and without the proposed cloud fraction formulation were very similar, thus suggesting that the model is not as sensitive as expected. An analysis of individual terms in the water vapor specific humidity prognostic equation was also performed in order to understand the detected low sensitivity. It is believed that, under the selected horizontal and vertical resolution, only stratiform precipitation can be efficiently captured by the model and the related precipitation fields are weakly modified by the chosen cloud fraction profile.