Effects of cloud parameterization on the simulation of climate changes in the GISS GCM
- Science Systems and Applications, Inc., New York, NY (United States)
- NASA/Goddard Space Flight Center, New York, NY (United States). Inst. for Space Studies
Climate changes obtained from five doubled CO{sub 2} experiments with different parameterizations of large-scale clouds and moist convection are studied by use of the Goddard Institute for Space Studies (GISS) GCM at 4{degree} lat x 5{degree} long resolution. The baseline for the experiments is GISS Model II, which uses a diagnostic cloud scheme with fixed optical properties and a convection scheme with fixed cumulus mass fluxes and no downdrafts. The global and annual mean surface air temperature change ({Delta}T{sub s}) of 4.2 C obtained by Hansen et al. using the Model II physics at 8{degree} lat x 10{degree} long resolution is reduced to 3.55 C at the finer resolution. This is due to a significant reduction of tropical cirrus clouds in the warmer climate when a finer resolution is used, despite the fact that the relative humidity increases there with a doubling of CO{sub 2}. When the new moist convection parameterization of Del Genio and Yao and prognostic large-scale cloud parameterization of Del Genio et al. are used, {Delta}T{sub s} is reduced to 3.09 C from 3.55 C. This is the net result of the inclusion of the feedback of cloud optical thickness and phase change of cloud water, and the presence of areally extensive cumulus anvil clouds. Without the optical thickness feedback, {Delta}T{sub s} is further reduced to 2.74 C, suggesting that this feedback is positive overall. Without anvil clouds, {Delta}T{sub s} is increased from 3.09 to 3.7 C, suggesting that anvil clouds of large optical thickness reduce the climate sensitivity. The net effect of using the new large-scale cloud parameterization without including the detrainment of convective cloud water is a slight increase of {Delta}T{sub s} from 3.56 to 3.7 C. The net effect of using the new moist convection parameterization without anvil clouds is insignificant.
- Sponsoring Organization:
- National Aeronautics and Space Administration, Washington, DC (United States); USDOE, Washington, DC (United States)
- OSTI ID:
- 332699
- Journal Information:
- Journal of Climate, Vol. 12, Issue 3; Other Information: PBD: Mar 1999
- Country of Publication:
- United States
- Language:
- English
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