Project to Intercompare Regional Climate Simulations (PIRCS): Description and initial results

The first simulation experiment and output archives of the Project to Inter compare Regional Climate Simulations (PIRCS) is described. Initial results from simulations of the summer 1988 drought over the central United States indicate that limited-area models forced by large-scale information at the lateral boundaries reproduce bulk temporal and spatial characteristics of m eteorological fields. In particular, the 500 hPa height field time average and temporal variability are generally well simulated by all participating models. Model simulations of precipitation episodes vary depending on the s cale of the dynamical forcing. Organized synoptic-scale precipitation syste ms are simulated deterministically in that precipitation occurs at close to the same time and location as observed (although amounts may vary from obs ervations). Episodes of mesoscale and convective precipitation are represen ted in a more stochastic sense, with less precise agreement in temporal and spatial patterns. Simulated surface energy fluxes show broad similarity wi th the First International Satellite Land Surface Climatology Project (ISLS CP) Field Experiment (FIFE) observations in their temporal evolution and ti me average diurnal cycle. Intermodel differences in midday Bowen ratio tend to be closely associated with precipitation differences. Differences in da ily maximum temperatures also are linked to Bowen ratio differences, indica ting strong local, surface influence on this field. Although some models ha ve bias with respect to FIFE observations, all tend to reproduce the synopt ic variability of observed daily maximum and minimum temperatures. Results also reveal the advantage of an intercomparison in exposing common tendenci es of models despite their differences in convective and surface parameteri zations and different methods of assimilating lateral boundary conditions.