中亚地区气溶胶时空分布及其对云和降水的影响

中亚地区属干旱半干旱气候区,是水资源缺乏最严重的地区之一,也是全球沙尘气溶胶贡献度较大的区域.利用MODIS气溶胶和云资料以及校准后的TRMM降水数据,可从宏观角度分析中亚地区气溶胶、云、降水的时空分布特征,研究气溶胶与云和降水之间的相互影响关系.结果表明:1中亚地区年平均气溶胶光学厚度表现为春季(0~1)夏季(0~0.8)冬季(0~0.42)秋季(0~0.38),2002—2013年间整体呈现增加趋势;冬季COD量值明显高于其他3个季节,12年间整体表现出下降趋势,夏季变化较小,增幅为-0.876%,冬季最大,增幅为-1.713%;云水路径的区域性和季节性变化较为明显,整体处于降低趋势,其中秋季的新疆塔里木盆地变化最为显著,年变化为-6.607%;利用实测降水数据对TRMM月降水数据进行校准处理,可有效提升数据精度,新疆境内夏季降水占年降水量的比重较大,春、秋次之,咸海地区降水量年内分配相对较均匀,季节性差异不明显,中亚干旱区作为一个整体,降水呈现出增加趋势,其中,冬季降水的增加趋势最明显.2气溶胶光学厚度与云光学厚度呈负相关;与云滴粒子有效半径关系复杂,受水汽影响较大,在云层含水量较低的情况下,云滴粒子与气溶胶光学厚度呈负相关,而在云层含水量较高的情况下,二者呈正相关;云水路径随着气溶胶光学厚度的增加而减小,随AOD的变化的敏感程度在秋季最高,冬季最低.3气溶胶和降水关系复杂,整体来看,中亚地区气溶胶抑制降水.

Temporal distribution of cloud and precipitation and their possible relationships with surface aerosols in Central Asia

Central Asia is located in the arid zone sensitive to climate change. It is one of the areas with the most serious water scarcity and giving great regional and global contributions of dust aerosols. In this study, we used aerosol optical depth (AOD) and cloud data from MODIS on board the Terra satellite and precipitation data from TRMM to study spatial and temporal characteristics of aerosol-cloud-precipitation interactions. The results showed that during 2002-2013, AOD in Central Asia was in a rising trend while cloud optical depth (COD) showed a decreasing trend with greater decrease in winter. Seasonally, AOD was high in spring and summer and low in autumn and winter while COD was significantly higher in winter than the other seasons. Regional and seasonal cloud water path (CWP) showed an overall downward trend, and the most significant decrease was found over Tarim Basin with the annual change rate of -6.607%. By calibrating the monthly precipitation data of TRMM using the measured rainfall data, it was found that precipitation in Xinjiang was mostly concentrated in summer, followed by spring and autumn. In comparison, no significant seasonal difference in precipitation was found in the Aral Sea region. Precipitation over central Asia showed an increasing trend, and the increase was the most significant in winter. Furthermore, AOD was negatively correlated with COD. It has a complex relationship between AOD and CER by the influence of water vapor. CER was negatively correlated with AOD in the case of lower water content of clouds while positively correlated at higher water content. CWP reduced with the increase of AOD, and the sensitivity was the highest in fall and lowest in winter. The relationship between aerosols and precipitation was complex. Generally speaking, aerosols suppressed precipitation in Central Asia.