Stochastic sub-grid scale clouds
|Scientific Discipline||Earth System Modelling - Atmospheres|
|Principal Investigator(s)||Heikki Järvinen|
|Leading Institution||Finnish Meteorological Institute, Finland|
|DEISA Home Site||CSC|
Representation of clouds and their interaction with radiation remains a major uncertainty in atmospheric general circulation models (GCMs) used in Earth System Modelling. In the SSSC-project, a recently developed stochastic approach will be tested with ECHAM5 atmospheric GCM, coupled with the Max Planck Institute Ocean model, MPIOM.
The scope of this work is on the subgrid-scale cloud features, that is, cloud features too small to be resolved by ordinary GCMs. The recently developed Monte Carlo Independent Column Approximation (McICA) allows flexible description of subgrid-scale cloud structure in radiation calculations. However, radiative fluxes and heating rates calculated with McICA contain stochastic noise. Two issues will be addressed: first, the impact of small-scale random noise associated with McICA on climate simulation of ECHAM5-MPIOM, and second, the impact of systematic changes in assumed subgrid-scale cloud structure.
A coupled atmosphere-ocean GCM is used in this study. This is required in order to avoid use of fixed sea surface temperature of an atmosphere-only GCM which would seriously limit the validity of the results obtained.