【作者】 吴伟；

【导师】 杨军； 李双林；

【作者基本信息】 南京信息工程大学 ， 大气物理学与大气环境， 2012， 硕士

【摘要】 本文使用全球大气模式(GFDL-AM2)对人为硫酸盐气溶胶直接气候效应进行了模拟,研究人为硫酸盐增长对上世纪70年代末长江中下游夏季降水年代际转型的影响,通过将模拟结果与观测和再分析资料进行对比,分析其影响机制。在此基础上,将硫酸盐和黑碳气溶胶的效应进行对比,并考察两者的协同作用。我们完成了两组集合试验,每组集合试验各由5个成员组成,每个成员是由一自1970至2000共31年的模式积分。在第一组试验中,模式被给定随时间演变的气溶胶强迫。在第二组试验中,在东亚区域,人为硫酸盐气溶胶被固定在1970年的水平不变,其余完全同第一组试验。第一组试验与第二组试验的差异被用来分析人为硫酸盐气溶胶的气候影响。从30年平均结果看,东亚区域的人为硫酸盐在大气顶和地面造成显著的负辐射强迫,最大值可达-3W·m-2,其引起的气温变化中国范围内绝大部分地区不超过-0.3-0.1℃,降水变化不超过-0.1-0.2mm·day-1。从年代际变化看,硫酸盐气溶胶增长引起的降水年代际变化与观测到的降水转型有很好的时空一致性,在长江中下游流域都表现为0.5-1mm·day-1的降水增多；观测中包括副热带高压西伸南移、我国东部近地面异常北风等夏季风年代际减弱信号以及对应的垂直温度、上升运动分布等均能很好地被模式再现。机制上,硫酸盐气溶胶通过引起负辐射强迫,造成我国中东部的大部分地区地面到对流层中层降温,其中地面最大降温幅度达到-1℃以上,由此海陆热力对比减小,使东亚夏季风减弱,雨带容易在长江中下游停留,从而导致该区域降水增多。于是,硫酸盐气溶胶增多对长江中下游降水年代际转型有重要贡献。与黑碳的对比以及对两种气溶胶协同作用的模拟表明：从年代际变化看,黑碳气溶胶在地表同样引起减温效应,大值可达-1℃,因此存在与人为硫酸盐类似的使夏季风减弱和长江流域降水增多的效应,量值同样可达0.5-1mm·day-1以上。而两种气溶胶协同作用则与单独作用体现出完全不同的特征：协同作用使长江以南降水减少达1mm·day-1以上,地表升温0.6-1℃。从机制上,两种气溶胶的协同作用阻断了中国东部夏季风的水汽输送,使整个中国东部夏季降水减少。两种气溶胶协同作用与单一气溶胶作用的关系是非线性的。更多还原

【Abstract】 To explore the direct effect of the increased anthropogenic sulfate aerosols concentration on the decadal shift of summer precipitation in the middle and lower reaches of the Yangtze River valley since the late-1970s, a global climate model (GFDL-AM2) is employed to conduct ensemble sensitive experiments. The results are compared with observation and reanalysis data to understand the mechanism for the impact. Then, this effect is compared with that of black carbon. Particularly, the synergy effect of the combined two kinds of aerosols is examined.Two sets of ensemble experiments are performed. Each ensemble constitutes5members with a31-year integration beginning from1970. In the first ensemble, the AGCM is prescribed with historically evolving aerosol forcing, while the anthropogenic sulfate aerosol is fixed at the level of1970over East Asia in the second ensemble. The difference of the first ensemble minus the second ensemble is used to analytze the impact of anthropogenic sulfate. As far as the30-year average is concerned, anthropogenic sulfate aerosols causes obvious negative radiative forcing at the top of atmosphere and the surface in East Asia from1971-2000, with the maximum close to-3W·m-2. It results in significant changes in temperature within (-0.3,0.1)℃and precipitation change within (-0.1,0.2) mm-day-1in most areas in China. As far as the interdecadal variation is concerned, the spatial-temporal structure shift of modeled summer rainfall bears a big similarity to the observed, exhibiting a rainfall increase in the middle and lower reaches of the Yangtze River. In particular, the shift characteristics in several East Asian Summer Monsoon subsystems, including the southward and westward stretch of the western Pacific subtropical high and the anomalous northerly along the east coast of East China as well as those in the vertical distribution of air temperature and vertical velocity, can be captured. Mechanisticly, the increased sulfate aerosols causes intensified negative radiative forcing, results in cooling in much of east China from the surface to the middle troposphere with the maximum cooling rate of more than-1℃on the surface. Subsequently, this weakens the land-sea thermal contrast and East Asian Summer Monsoon, and favors the rainband staying in the Yangtze River basin rather than moving northward to North China and Northeast China in middle summer (July-August). Thus, it is concluded that the increased anthropogenic sulfate aerosols have contributed substantially to the decadal shift of summer precipitation in the middle and lower reaches of the Yangtze River since the late-1970s.When it is compared with Black carbon(BC), BC causes a surface temperature cooling close to-1℃and weakened summer monsoon and increased precipitation in the Yangtze River basin, which are similar to those of anthropogenic sulfate. Synergy impact of the combined two kinds of aerosols shows completely different characteristics in that decreased precipitation close to-1mm-day-1and warmed surface air temperature as large as0.6-18℃are seen over the south of the Yangtze River. A further analysis displays that synergy impact of the two kinds of aerosols tends to block moisture transport toward east Asia, causing decreased precipitation in eastern China. This suggests that the synergy impact of the combined two kinds of aerosols is different from the sum of their individual impacts. Thus, a nonlinear interaction between the impacts of the two kinds of aerosols may exist更多还原