RELATIONS BETWEEN WINTER PRECIPITATION AND ATMOSPHERIC CIRCULATION SIMULATED BY THE GEOPHYSICAL FLUID-DYNAMICS LABORATORY GENERAL-CIRCULATION MODEL

General circulation model (GCM) simulations of atmospheric circulation are more reliable than GCM simulations of temperature and precipitati on. Thus, some researchers are developing empirical relations between observed atmospheric circulation and observed temperature and precipit ation to translate GCM estimates of future atmospheric circulation int o estimates of future regional temperature and precipitation. Developi ng climate-change scenarios in this manner assumes, at least, that rel ationships between atmospheric circulation and surface climate variabl es, such as temperature and precipitation, are properly simulated by G CMs. In this study, temporal correlations between 700 hPa height anoma lies (700 hPa anomalies) over North America simulated by the Geophysic al Fluid Dynamics Laboratory (GFDL) GCM and GFDL-GCM-simulated (GFDL-s imulated) winter precipitation at eight locations in the conterminous United States are compared with corresponding correlations in observat ions. The objectives are to (i) characterize the relations between atm ospheric circulation and winter precipitation simulated by the GFDL GC M for selected locations in the conterminous USA, (ii) determine wheth er these relations are similar to those found in observations of the a ctual climate system, and (iii) determine if GFDL-simulated precipitat ion is forced by the same circulation patterns as in the real atmosphe re. Results indicate that the GFDL GCM simulates relations between 700 hPa anomalies and local winter precipitation that are similar to rela tions found in observed data for most of the locations analysed in thi s study. Results also indicate that at regional scales GFDL GCM simula tions of the relations between 700 hPa anomalies and winter precipitat ion are most similar to observed relations for locations near oceanic sources of atmospheric moisture. These results suggest that the GFDL G CM may not adequately simulate variations in advection of atmospheric moisture into the interior parts of the USA and!or that this moisture is not adequately converted into precipitation in the interior parts o f the country. This problem may be due, in part, to (i) the inadequate representation of topography in the GFDL GCM, (ii) stronger-than-obse rved mean winter zonal winds simulated by the GFDL GCM and the consequ ent more west-to-east paths of air flow and storm systems across North America, (iii) the relative weakness of important synoptic patterns i n CFDL simulations, such as the Pacific North American circulation pat tern, and (iv) the occurrence of 'spectral rain'. In addition, for som e locations, the GFDL-simulated relationships between precipitation an d 700 hPa anomalies can be quite different from observed relations. Th e differing relationships suggest that GFDL-simulated changes in xregi onal precipitation in response to changes in atmospheric circulation c ould differ from changes that would occur in the actual climate system .