Variable resolution general circulation models:: Stretched-grid model intercomparison project (SGMIP)

Variable resolution general circulation models (GCMs) using a global stretched grid with enhanced uniform resolution over the region(s) of interest have proven to be an established approach to regional climate modeling providing an efficient regional downscaling to mesoscales. This approach has been used since the early to mid-1990s by climate modeling groups from France, the United States, Canada, and Australia, among others, along with or as an alternative to the current widely used nested-grid approach. Stretched-grid GCMs are used for continuous/autonomous climate simulations, as are usual GCMs, with the only difference being that variable resolution grids are used instead of more traditional uniform grids. The important advantages of variable resolution stretched-grid GCMs are that they do not require any lateral boundary conditions/forcing and are free of the associated undesirable computational problems; as a result, they provide self-consistent interactions between global and regional scales of motion and their associated phenomena as in uniform grid GCMs. The international stretched-grid model intercomparison project, phase 1 (SGMIP-1), using variable resolution GCMs developed at major centers/groups in Australia, Canada, France, and the United States, was initiated in 2001 and successfully conducted in 2002-2005. The results of the 12-year (1987-1998) climate simulations for a major part of North America are available at the SGMIP Web site: http://essic.umd.edu/similar to foxrab/sgmip.html. The SGMIP-1 multimodel ensemble results for the region compare well with reanalysis and observations in terms of spatial and temporal diagnostics. Regional biases for time-averaged model products are mostly limited to about half (or less) of typical reanalysis errors, i.e., within the uncertainties of the available reanalyses, while a high quality of global circulation is preserved. SGMIP products are available to national and international programs such as the World Meteorological Organization/World Climate Research Program/Working Group on Numerical Experimentation (WMO/WCRP/WGNE).