Cloud and Surface Processes and Parameterizations

One of the two primary scientific programs in the MMM division is the Cloud and Surface Processes and Parameterizations (CaSSP) Program. The main goals of this program are to quantify the large-scale effects of mesoscale and microscale processes and to develop physically based methods to account for these effects in large-scale models. Until this is done, predictions from large-scale models - including both weather forecasts and forecasts of climate change - will be of limited accuracy. The emphasis within MMM is on understanding how the atmosphere, land and ocean surface and hydrological processes interact, and how these processes can be quantified. This effort includes five key research areas: deep convective cloud systems, microphysics, boundary-layer clouds, surface-atmosphere interactions and the physical chemistry of clouds. Two important components of this effort are nonhydrostatic, fine-scale models using large-eddy simulation, and cloud-resolving models. These allow high-resolution definition of the mesoscale and microscale systems involved and are therefore useful for testing methods to quantify the effects of these processes on larger scales. Critical for the success of this program is the evaluation of these models against detailed observational studies of the underlying physical processes. The program contributes to the objectives of the WCRP Global Energy and Water-cycle Experiment (GEWEX) and the Cloud System Study (GCSS) component of GEWEX as well as to the objectives of USWRP.