HR: 0800h
AN: A41D-0747    [Abstracts]
TI: Effects of Aerosols on Clouds and Precipitation in the UCLA GCM
AU: * Gu, Y
EM: gu@atmos.ucla.edu
AF: UCLA, Department of Atmospheric and Oceanic sciences, 405 Hilgard Ave. 7127 math Sciences, Los Angeles, CA 90095, United States
AU: Liou, K
EM: knliou@atmos.ucla.edu
AF: UCLA, Department of Atmospheric and Oceanic sciences, 405 Hilgard Ave. 7127 math Sciences, Los Angeles, CA 90095, United States
AB: The UCLA atmospheric general circulation model (AGCM) has been used to investigate the effect of aerosols on the simulated cloud fields and precipitation. This model includes an efficient and physically based radiation parameterization scheme specifically developed for application to clouds and aerosols. Including a background aerosol optical depth of 0.2 produces a decrease in precipitation in the tropics as a result of decreased temperature contrast between this area and the mid- to high latitudes, which suppresses tropical convection. This decrease has corrected an overestimate in precipitation of about 0.34-0.4 mm day-1 in the UCLA AGCM simulations. The total cloudiness is reduced by about 2.0% for both January and July simulations. Reduction in the total cloudiness is consistent with the positive solar forcing at the top of the atmosphere such that the induced cloud feedback dominates aerosol direct effect. Since aerosols stem from local sources, we further investigated the effect of an extremely polluted area such as that occurring in China on climate simulation. The experiment with increased aerosol optical depths in China shows a noticeable enhancement in the July precipitation in the southern part of China and Indian areas due to cooling in the midlatitudes that leads to the strengthening of the Hadley circulation. A series of climate experiments incorporating various aerosol types have also been performed. Large dust particles and black carbon in China would heat the air column in the mid- to high latitudes that tends to shift the simulated precipitation inland, i.e., toward the Himalayas. The climatic effects of aerosols on the radiative budget, temperature, and precipitation fields are not only produced through their direct radiative forcings, but also affected by the subsequent modulation of cloud fields formed in the model. This ˇ°indirectˇ± effect through clouds generated in the UCLA AGCM is comparable to direct aerosol radiative forcing. Finally, we are testing the parameterization of ice clouds and aerosols and their radiative forcings in the most recent Weather Research Forecasting (WRF) model that has been used as the foundation for the construction of a regional climate model encompassing land, coastal ocean, and the atmosphere, specifically designed for application to California.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0321 Cloud/radiation interaction
DE: 1626 Global climate models (3337, 4928)
DE: 3311 Clouds and aerosols
DE: 3359 Radiative processes
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting