气溶胶对东亚夏季风指数和爆发的影响及其机理分析

THE ANALYSIS OF MECHANISM OF IMPACT OF AEROSOLS ON EAST ASIAN SUMMER MONSOON INDEX AND ONSET

利用高分辨率区域气候模式Reg CM4.3,通过引入沙尘、海盐、硫酸盐、黑碳和有机碳等5种气溶胶,对1995—2010年的东亚夏季风进行数值模拟,研究了自然和人为气溶胶对东亚夏季风的可能影响。结果表明:区域气候模式对东亚夏季风和气溶胶的时空分布都有较好的模拟效果,自然和人为气溶胶造成东亚夏季风指数减小约5%,且除我国东南部地区外,气溶胶使整个季风区的季风爆发时间推迟了1候左右。在我国东南部及近海地区,气溶胶通过吸收太阳辐射对中层大气起到加热作用,气柱受热会出现膨胀,从而造成了低层大气的位势高度下降并激发出气旋式环流距平,气旋式环流距平西侧偏北风能削弱东亚夏季风区低层的偏南气流。气溶胶的加入引起的地表负的辐射强迫造成了空气出现下沉运动并配合低层偏北风和高层偏南风距平,在25°N以北地区形成了间接经向环流距平,从而也削弱了东亚夏季风的垂直环流。气溶胶增加了我国季风区的水汽通量散度值,从而造成了夏季降水的明显减少,其中我国华北和西南地区为2个主要的降水减少区域。

Reg CM4.3, a high-resolution regional climate model, which includes five kinds of aerosols（dust, sea salt, sulfate, black carbon and organic carbon）, is employed to simulate the East Asian summer monsoon（EASM） from 1995 to 2010 and the simulation data are used to study the possible impact of natural and anthropogenic aerosols on EASM. The results show that the regional climate model can well simulate EASM and the spatial and temporal distribution of aerosols. The East Asian summer monsoon index is reduced by about 5% by the natural and anthropogenic aerosols and the monsoon onset time is also delayed by about a pentad except for Southeast China. The aerosols heat the middle atmosphere through absorbing solar radiation and the air column expands in Southeast China and its offshore areas. As a result, the geopotential height decreases and a cyclonic circulation anomaly is generated in the lower atmosphere. Northerly wind located in the west of cyclonic circulation weakens the low-level southerly wind in the East Asian summer monsoon region. Negative surface radiative forcing due to aerosols causes downward motion and an indirect meridional circulation is formed with the low-level northerly wind and high-level southerly wind anomaly in the north of 25°N in the monsoon area, which weakens the vertical circulation of East Asian summer monsoon. The summer precipitation of the monsoon region is significantly reduced, especially in North and Southwest China where the value of moisture flux divergence increases.