沙尘气溶胶直接气候效应对东亚冬季风影响的模拟研究

A Numerical Simulation Study on the Impacts of Dust Aerosol Direct Climatic Effects on the East Asian Winter Monsoon

利用东亚沙尘复折射指数数据和较新的植被分布对区域气候—沙尘耦合模式(Reg CM4-Dust)的沙尘光学特性和沙源区域进行了更新。在此基础上,研究了沙尘气溶胶直接辐射效应对东亚冬季风的影响。模拟结果表明,引入沙尘效应后,东亚大陆绝大部分季风区对流层低层冬季风环流增强。同时,对流层中、上层中低纬度纬向风增强而中高纬度纬向风减弱,导致中高—中低纬度之间纬向风经向切变加强,从而有利于中高纬度冷空气向南侵入,这是低层冬季风环流增强在中上层的反映。另外,沙尘气溶胶导致东亚绝大部分季风区降水明显减少,东北地区西南部、华北大部、黄土高原、黄淮以及长江中下游流域减少达10%以上,这是降水对冬季风增强的响应。沙尘气溶胶引起冬季东亚次大陆—西北太平洋之间温度梯度增大,进而导致海陆间湿静力能梯度增大,是导致东亚大陆冬季风增强的主要原因。

Data of complex refractive index of East Asian dust and the latest vegetation distribution were used to update the default optical properties of dust aerosols and desert area in the regional climate-dust coupling model Reg CM4-Dust. Then, the direct effect of dust aerosols on the East Asian winter monsoon（EAWM） was studied. The simulation results showed that the dust effects caused an enhancement of EAWM circulation in the lower troposphere in most of the EAWM area. In addition, the zonal wind was increased over mid-high latitudes and decreased over mid-low latitudes in the middle and upper troposphere. This can strengthen the meridional shear of zonal wind and favor the southward invasion of cold air, resulting in a strengthening EAWM. The dust effects also induced an obvious reduction of winter precipitation, whichwas in response to a strengthening EAWM, especially in the winter monsoon prevailing areas such as the southwestern part of northeastern China, North China, the Loess Plateau, and the middle and lower reaches of the Yangtze River, where the precipitation can decrease 10% or more. The increase in the temperature gradient between the East Asian subcontinent and the northwestern Pacific, which can enlarge the gradient of moist static energy（MSE）, was the main reason for an enhancement of monsoon circulation when the dust effects were accounted for.