夏季硫酸盐和黑碳气溶胶对中国云特性的影响

利用WRF-Chem（Weather Research and Forecasting model coupled with Chemistry）模式研究2006年8月1日—9月1日中国区域硫酸盐和黑碳气溶胶对云特性的影响。模式验证利用了卫星和地面观测的气象要素、化学物质浓度、气溶胶光学特性和云微物理特性。模式性能评估表明该模式能较好地抓住气象要素（温度、降水、相对湿度和风速）的量级和空间分布特征。通过与地面观测和MODIS卫星数据对比发现，尽管模式模拟还存在偏差，但还是能较好模拟出气溶胶物种的地表浓度、气溶胶光学厚度（AOD）、云光学厚度（COD）、云量（CLDF）、云顶云滴有效半径（CER）和云水路径（LWP）。通过两个敏感性试验（分别增加二氧化硫和黑碳排放量至控制试验排放的3倍）与控制试验的对比发现硫酸盐比黑碳更易成为云凝结核，在中国东部云顶云滴数浓度和其它云特性参数对二氧化硫排放增加的响应均从北向南呈递增，这与地面湿度分布有关。云滴有效半径对硫酸盐气溶胶的响应符合气溶胶第一间接效应的定义，即硫酸盐气溶胶增多，云滴数浓度增加，云滴有效半径减少，但是对黑碳气溶胶的响应在各区域不尽相同。还发现黑碳对云量的影响远大于硫酸盐，主要原因是由于黑碳气溶胶直接辐射效应（对太阳光的吸收）导致的云的“燃烧”作用。 

THE IMPACT OF SULFATE AND BLACK CARBON AEROSOLS ON SUMMERTIME CLOUD PROPERTIES IN CHINA

We investigate the impacts of sulfate and black carbon aerosols on cloud microphysical properties over China during 1 August-1 September, 2006, by using the WRF-Chem model (Weather Research and Forecasting model coupled with Chemistry). A comprehensive model evaluation is performed for simulated meteorology, aerosol concentrations, aerosol optical properties, as well as cloud variables by using the ground-based and satellite observations across China. The model simulates well the meteorological variables such as surface air temperature, precipitation, relative humidity, and wind speed, in terms of both magnitudes and spatial distributions. Simulated concentrations of sulfate, nitrate, organic carbon, black carbon, aerosol optical depth(AOD), aerosol single scattering albedo(SSA), cloud top effective radius (CER), cloud optical thickness(COD), and liquid water path(LWP) have relatively large biases. The impacts of sulfate and black carbon on cloud properties are quantified by two sensitive simulations with tripled emissions of sulfur dioxide and black carbon, respectively. Sulfate is found to be more important than black carbon as they serve as cloud condensation nuclei. The sensitivity of cloud-top cloud droplet number concentrations over eastern China to sulfate aerosol is found to increase from the North to South China, as a result of the higher relative humidity in South China. The simulated changes in effective radius of cloud droplets follow the Twomey Effect when concentrations of sulfate increase, but those in effective radius of cloud droplets differ as concentrations of black carbon increase. Compared to sulfate, black carbon aerosol is found to have a much more important effect on cloud fraction in eastern China as a result of the cloud "burning" effect caused by the absorption of sunlight.