Comparing clouds and their seasonal variations in 10 atmospheric general circulation models with satellite measurements
M. H. Zhang, W. Y. Lin, S. A. Klein, J. T. Bacmeister, S. Bony, R. T. Cederwall, A. D. Del Genio, J. J. Hack, N. G. Loeb, U. Lohmann, P. Minnis, I. Musat, R. Pincus, P. Stier, M. J. Suarez, M. J. Webb, J. B. Wu, S. C. Xie, M.-S. Yao, J. H. Zhang
Journal of Geophysical Research, May 2005. doi:10.1029/2004JD005021.

Abstract

To assess the current status of climate models in simulating clouds, basic cloud climatologies from 10 atmospheric general circulation models are compared with satellite measurements from the International Satellite Cloud Climatology Project (ISCCP) and the Clouds and Earth's Radiant Energy System (CERES) program. An ISCCP simulator is employed in all models to facilitate the comparison. Models simulated a four-fold difference in high-top clouds. There are however also large uncertainties in satellite high thin clouds to effectively constrain the models. The majority of models only simulated thirty to forty percent of middle-top clouds in the ISCCP and CERES datasets. Some models only simulated less than a quarter of observed middle clouds. Half of the models underestimated low clouds while none overestimated them at a statistically significant level. When stratified in the optical thickness ranges, the majority of the models simulated optically thick clouds more than twice the satellite observations. Most models however underestimated optically intermediate and thin clouds. The grand mean of all models simulated about eighty percent of optical intermediate clouds and sixty percent of optically thin clouds in observations. Compensations of these clouds biases are used to explain the simulated longwave and shortwave cloud radiative forcing at the top of the atmosphere.

Seasonal sensitivities of clouds are also analyzed to compare with observations. Models are shown to simulate seasonal variations better for high clouds than for low clouds. Latitudinal distribution of the seasonal variations correlate with satellite measurements at >0.9, 0.6 to 0.9, and -0.2 to 0.7 respectively for high, middle and low clouds. Seasonal amplitudes of individual ISCCP cloud types differ among the models and with observations by as much as several hundred percent. The seasonal sensitivities of cloud types are found to strongly depend on the basic cloud climatology in the models. Models that systematically underestimate middle clouds also underestimate seasonal variations, while those that overestimate optically thick clouds also overestimate their seasonal sensitivities. Possible causes of the systematic cloud biases in the models are discussed.

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