Radiative characteristics of the Canadian Climate Centre second- generation general circulation model

Abstract

The GCM data were obtained from the Atmospheric Model Intercomparison Project (AMIP) simulation. Data corresponding to the period January 1985 through December 1988 were examined since this period of the AMIP simulation overlaps with the Earth Radiation Budget Experiment (ERBE) and the International Satellite Cloud Climatology Project (ISCCP) datasets. Ocean albedos are too high in the Tropics and too low in the polar regions relative to surface observations and theoretical estimates. Compared to a satellite-derived dataset, however, they are slightly underestimated. Throughout much of the Sahara and Saudi Deserts surface albedos are too low, while for much of Western Australia they are too high. Like many GCMs, the CCC model has too little atmospheric H2O vapor. This results in too much outgoing longwave radiation from clear skies, especially in the Tropics. Neglect of all trace gases except for CO2 and weak H2O vapor absorption exacerbate this bias. Cloud radiative forcing CRF from the GCM was compared to CRF obtained from ERBE data. Globally averaged, net CRF is in excellent accord with observations but shorwave and longwave CRFs are too strong. Zonal averages, however, reveal biases in which clouds act to cool the Tropics too much and cool the high latitudes too little during summer, yet they warm polar regions too much during winter. -Authors