Aerosol Effects on Climate and Climate Change of the Pacific Rim Region

摘要

An understanding of the aerosol-climate relationship is crucial for explaining past climate trends and improving climate predictions. Since aerosols are transported through the large-scale circulation and intimately interact with cloud and radiative processes, a general circulation model (GCM) that incorporates various interactive atmospheric components should be employed for process studies. We have conducted and analyzed climate simulations using the atmospheric general circulation model (AGCM) developed at the University of California, Los Angeles (UCLA) to provide comprehensive atmospheric responses to the aerosol effects that may not be available from observations. An efficient and physically based radiation and cloud parameterization schemes have been developed and incorporated in the UCLA AGCM that can better determine the cloud optical properties and provide more accurate radiative heating fields. With all the advanced features in the new radiation scheme, the updated UCLA AGCM is better suited for application in a variety of climate studies, including the effect on climate of increased anthropogenic aerosols. Using this model, we have performed a series of numerical experiments incorporating the aerosol optical depths observed in China and various aerosol compositions to investigate the aerosol effects on regional climate. Results show that inclusion of the background aerosol optical depth of 0.2 reduces the global mean net surface solar radiation by about 7 W m-2, and also produces a decrease in precipitation. The increased aerosol optical depths in China further reduce the surface solar insolation by about 7 W m-2 in July, partly associated with the increase in cloud cover through aerosol-radiation-cloud interaction. The corresponding precipitation in southern China and north Indian Ocean is also enhanced in July due to the increased aerosol optical depths, especially in the southern part of China, where moisture supply is sufficient. The effect of aerosol constituents is also important in terms of the global mean radiation budget.