We present preliminary results of regional climate models participating in the Project to Intercompare Regional Climate Simulations (PIRCS). The goal of PIRCS is to advance the state of regional climate modeling by a series of systematic intercomparisons. PIRCS Experiment 1 is devoted to two sharply contrasting hydrologic regimes, namely the drought of 1988 and the regional flood of 1993 in the central U.S. Here we discuss preliminary results for Experiment 1a, which is devoted to the 1988 drought.
The simulation domain covers the continental U.S. and adjacent regions with an outer buffer region in which large-scale forcing is imposed. When forced by boundary conditions from the NCEP/NCAR reanalysis all models are able to recover the patterns of mean 500 mb height over the simulation domain. The standard deviation of the 500 mb heights, which reflects synoptic-scale storm tracks, also is well reproduced.
Analysis of predicted precipitation focuses on a portion of the Upper Mississippi River basin that is well resolved from the standpoint of a regional model (of order 400 grid points) but poorly resolved in terms of a GCM or the NCEP/NCAR Reanalysis. Comparison to observed precipitation indicates that the models generally are able to replicate wet and dry periods in the observations, though amounts may be underpredicted or overpredicted. All models capture the lateral boundary forcing as indicated by the timing of specific precipitation episodes. Departures from the observed precipitation trend increased somewhat toward the end of the period and may point to the implications of soil moisture feedbacks. Although the nocturnal maximum in precipitation over the central U.S. is not as pronounced as is observed, the models represent the nocturnal maximum substantially better than the NCEP/NCAR reanalysis.
These results indicate that while details of the predictions differ from model to model, regional climate models in general are able to reproduce observed dynamical fields and timing of precipitation episodes when provided with appropriate observed forcing at their lateral boundaries.
NOTE: Not all authors could be listed because of the limitations of the electronic modification form. Full author list is R. Arritt, W.J. Gutowski, Z. Pan, R. Silva, E.S. Takle, D. Caya, S. Chen, J.H. Christensen, S.-Y. Hong, J. Katzfey, W. Lapenta, R. Laprise, P. Lopez, J. McGregor, and J. Roads