The Atmospheric Model Intercomparison Project (AMIP) was initiated in 1989 to systematically validate, diagnose, and compare the performance of atmospheric general circulation models (GCMs). The project required models to simulate the climate from 1979–88 under observed boundary conditions, including monthly average temperature, sea ice, and prescribed CO₂ and solar constant. By 1995, 31 modeling groups had contributed data, which were analyzed by the Program for Climate Model Diagnosis and Intercomparison (PCMDI) and various subprojects. The results showed that the ensemble mean of AMIP models reasonably matched observed large-scale seasonal distributions of pressure, temperature, and circulation, though there were significant intermodel differences in precipitation and ocean heat flux, particularly in low latitudes. Total cloudiness was poorly simulated, especially in the Southern Hemisphere. The models generally reproduced the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific, though they underestimated the amplitude of major El Niños. The ensemble mean of precipitation and ocean surface heat flux showed good agreement with observations, but there were large intermodel differences in low latitudes. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the amplitude of major El Niños. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the amplitude of major El Niños. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the amplitude of major El Niños. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the amplitude of major El Niños. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the amplitude of major El Niños. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the amplitude of major El Niños. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the amplitude of major El Niños. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the amplitude of major El Niños. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the amplitude of major El Niños. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated theThe Atmospheric Model Intercomparison Project (AMIP) was initiated in 1989 to systematically validate, diagnose, and compare the performance of atmospheric general circulation models (GCMs). The project required models to simulate the climate from 1979–88 under observed boundary conditions, including monthly average temperature, sea ice, and prescribed CO₂ and solar constant. By 1995, 31 modeling groups had contributed data, which were analyzed by the Program for Climate Model Diagnosis and Intercomparison (PCMDI) and various subprojects. The results showed that the ensemble mean of AMIP models reasonably matched observed large-scale seasonal distributions of pressure, temperature, and circulation, though there were significant intermodel differences in precipitation and ocean heat flux, particularly in low latitudes. Total cloudiness was poorly simulated, especially in the Southern Hemisphere. The models generally reproduced the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific, though they underestimated the amplitude of major El Niños. The ensemble mean of precipitation and ocean surface heat flux showed good agreement with observations, but there were large intermodel differences in low latitudes. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the amplitude of major El Niños. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the amplitude of major El Niños. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the amplitude of major El Niños. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the amplitude of major El Niños. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the amplitude of major El Niños. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the amplitude of major El Niños. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the amplitude of major El Niños. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the amplitude of major El Niños. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the amplitude of major El Niños. The models' simulation of the seasonal cycle of sea level pressure and interannual variability in the tropical Pacific was reasonably close to observations, though they underestimated the