Direct Radiative Effect of Dust in the UCLA AGCM
| Yu Gu | University of California, Los Angeles |
| Kuo-Nan Liou | UCLA |
Category: Aerosols
Although dust is one of the major causes for environmental and public health concerns, it also has significant impact on regional and global climate. Dust aerosols, especially those with large sizes, can scatter and at the same time absorb solar and terrestrial radiation, leading to the positive and negative effects of aerosol direct forcing. The solar and infrared radiative forcings of dust may be of different signs, thus further complicating the total forcing assessment. Determination of the sign and magnitude of direct radiative forcing by dust on regional and global scales appears to remain a key unsolved problem. Since aerosols are transported through the large-scale circulation and intimately interact with cloud and radiative processes, more detailed studies are required by using an atmospheric general circulation model (AGCM) that incorporates various interactive atmospheric processes. The University of California at Los Angeles AGCM has been used to investigate the direct radiative effect of dust aerosols on the simulated radiation budget and precipitation. This model includes an efficient and physically based radiation parameterization scheme specifically developed for application to clouds and aerosols. Since aerosols stem from local sources, we investigate the effect of an extremely polluted area such as that occurring in China on climate simulation. Through both scattering and absorption, large dust particles significantly reduce the global solar flux reaching the surface by more than 7 W m-2 in the July AGCM simulation, while a positive solar forcing is found at the top of the atmosphere due to substantial absorption. Dust particles also have a significant effect on infrared radiation under clear conditions. However, their infrared effect at the top of the atmosphere in climate simulation is significantly reduced when clouds are present. Large dust particles increase the heating of the atmospheric column of mid- to high latitudes, which weakens meridional circulation and shifts precipitation landward, e.g., toward the Himalayas such that rainfall occurs over north of the Bay of Bengal. Incorporating a large loading of dust particles in the simulation increases precipitation in northwestern China where it is normally dry, and therefore tends to reduce the occurrence.
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