Regional climate simulation of the anomalous U.S. Climate events with a variable resolution stretched grid GCM

A variable resolution GCM using a global stretched grid (SG) with fine resolution over an area of interest, is a viable new approach to regional and subregional climate studies and applications. It is an alternative to the widely used nested grid approach introduced a decade ago as a pioneering step in regional climate modeling. The stretched grid approach is coming mostly from the global or GCM modelers as a new application of global models in the variable resolution framework, with enhanced regional resolution for both prognostic fields and surface boundary forcing. The stretched grid GCM is an ideal tool for a consistent representation of global and regional scale inter- actions.

The GEOS SG-GCM is used for simulations of the anomalous U.S. climate events of 1988 drought, 1993 flood, and 1998 El Nino impact, with 60 km regio- nal resolution. The height, low level jet, precipitation and other diagnostic patterns and characteristics are successfully simulated. The efficient down- scaling to mesoscales is obtained.

The special SG-runs are performed for participation in the WMO/WGNE PIRCS (Project to Intercompare Regional Climate Simulations).

The experiments with finer 0.5 degree (and higher) regional resolution, are under way. Other anomalous regional climate events will be simulated.

It is planned to develop the stretched grid version of the new NASA/NCAR GCM.

The key objectives of the study are: 1)obtaining an efficient down-scaling over the area of interest with fine and very fine resolution; 2) providing consistent interactions between regional and global scales including the con- sistent representation of regional energy and water balances; 3) providing a high computational efficiency for future SG-GCM versions using parallel codes.