Regional climate simulations over the continental United States during the summer of 1988 driven by a GCM and the ECMWF analyses

A regional climate model is driven at its lateral boundaries by the European Center for Medium Range Forecast (ECMWF) analyses and the GENESIS global climate model (GCM) during the Spring and summer of 1988. Observed sea surface temperatures (SSTs) are imposed as boundary conditions in the GCM. The regional climate simulations are integrated from April 1, 1988 through September 1, 1988 using a horizontal grid spacing of 108 km over the continental United States. The largest differences in both the atmospheric circulation and the surface climate of the regional climate simulations with GCM boundary conditions occur during June of 1988 when compared to the analyses or observations. The primary cause for the different results in the regional climate simulations is the lack of an anomalous upper level circulation in the GCM. In summary, the regional model does not add additional value to the large-scale patterns, which show the same systematic bias as the GCM. However, precipitation in the regional model is closer to observations when compared to the GCM. This implies that the use of an ensemble average to provide boundary conditions in conjunction with improved physics of the regional model may enhance the regional detail that is absent in low resolution GCMs. (C) 2000 Elsevier Science B.V.