Effects of cloud superparameterization at the land-atmosphere interface

Abstract:

Problems exist in simulating land-atmosphere coupling in modern GCMs. The effect of including explicit boundary layer dynamics via cloud superparameterization (SP) on land-atmosphere coupling is analyzed in several versions of the SP Community Atmosphere Model (SPCAM). Super-parameterization impacts both the net radiative input to the land-surface and the partitioning of sensible and latent heating with a distinct signature. We separate the effects of atmospheric processes, especially cloud radiative properties, from land-surface processes, especially soil-moisture dynamics, using a series of free-running and hindcast simulations. Effects of SP include reducing the coupling strength in the Central Great Plain in American, and reverses the terrestrial segment coupling sign (from negative to positive) over India. Analysis of the triggering feedback strength (TFS) and amount feedback strength (AFS) shows SP can capture the patterns of these indices over North America, with probability of afternoon precipitation enhanced by high evaporative fraction along the eastern United States and Mexico, while conventional versions of CAM struggle to capture this signal.