A COMPARISON OF GCM-SIMULATED AND OBSERVED MEAN JANUARY AND JULY SURFACE AIR-TEMPERATURE

January and July surface air temperature fields simulated by the GFDL, OSU, GISS, and UKMO general circulation models (GCMs) are compared to the global surface air temperature climatology compiled by Legates an d Willmott. Legates and Willmott's climatology was selected as the ver ification standard because it provides better spatial and temporal cov erage than its predecessors, such as the frequently employed RAND clim atology compiled in the early 1970s. Difference maps between each GCM- simulated field and the Legates and Willmott climatology are presented and evaluated. Zonal averages by 10-degrees latitudinal bands for eac h GCM as well as for the Legates and Willmott and RAND climatologies a lso are examined. Results indicate that surface air temperature simula tions are greatly influenced by model representations of topography, s ea level pressure, and precipitation. Inclusion of the diurnal cycle a nd the type of ocean model used also impact simulated surface air temp eratures. Mean January and July surface air temperatures are well simu lated by the GISS and UKMO models, whereas temperatures are overestima ted by the OSU GCM and underestimated by the GFDL GCM. GISS and UKMO s imulations seem even more accurate, on the average, than the data cont ained in the RAND observation-based climatology. Simulated equatorial air temperatures are slightly higher than observed, particularly in th e Southern Hemisphere. Model simulated air temperatures between 30-deg rees-S and 60-degrees-S are usually lower than observed, while air tem peratures poleward of 60-degrees-S are overestimated. Northern Hemisph ere temperatures are generally better simulated than their Southern He misphere counterparts.