近年来长江流域气溶胶光学厚度时空变化特征分析

利用2000年3月至2011年2月MODIS Level3遥感反演大气气溶胶光学厚度（AOD）产品数据，结合中国地形的3大阶梯分布，分析近年来长江流域气溶胶光学厚度的时空变化特征。结果表明，近12年来，长江流域的年平均AOD值在0．38,～,0．44之间变化，其中“第一阶梯”年平均AOD呈极显著下降趋势（P〈0．01），“第二阶梯”和“第三阶梯”则呈上升趋势，但趋势不显著（P〉0．05）；4季平均AOD除春季呈下降趋势，其他3季均为上升趋势，其中冬季上升速率最快，线性倾向率为0．004·a-1（P〈0．05），春季AOD与其他季节的差距在逐步减小；长江流域3大阶梯AOD具有鲜明的季节变化特征，基本上是春夏季较大，秋冬季较小，具体表现为春季最大，从夏季到冬季逐渐减小，冬季到来年春季跳跃性增高，但由于地理位置、地形、气候、人类活动等因素的影响，不同区域又有所差异；AOD年平均值和四季平均值均表现为“第三阶梯”〉“第二阶梯”〉“第一阶梯”。长江流域年平均AOD变化空间差异显著，其中显著减少区域占整个流域面积的17．54％，主要分布在“第一阶梯”；显著增加的区域仅占流域总面积的5．23％，主要分布在“第二阶梯”和“第三阶梯”。另外，由于海拔、地形及山脉阻挡等诸多因素影响，导致在地形阶梯间高程突变线左右两边的狭窄区域，AOD分布存在低处明显大于高处的现象。这些结果有助于长江流域的区域气候变化和环境研究。

Spatio-temporal variations of aerosol optical depth in the Yangtze River Basin during 2000 2011

Based on the monthly data of MODIS Level 3 and the terrain of three ladder distribution in China, the spatio-temporal variabilities of Aerosol Optical Depth （AOD） in the Yangtze River basin has been analyzed from March 2000 to February 201 l. The results showed that the areal annual mean AOD varied between 0.38 and 0.44 for the whole Yangtze River basin during 2000-2011, while the annual AOD varied greatly for the different terrain of three ladder distribution in the Yangtze River basin. Significant decreasing trends can be found in the first step, and increasing but not significant trends occurred in the second step and third step. Moreover, increasing trends can be found in summer, autumn and winter and the greatest increasing trend appeared in winter with a tendency rate was 0.004·a-1, while the seasonal mean AOD in spring had a descending trend. The gap of the mean AOD between spring and the other seasons also reduced gradually. Aerosol Optical Depth in the three steps of Yangtze River basin had distinctly seasonal changing characteristics which showed higher value occurred in spring and summer and lower value appeared in autumn and winter. The seasonal characteristics showed that the mean AOD of spring was the largest, then the AOD decreased gradually from summer to winter, while it took a leap rise from winter to next spring. However, different characteristics can be found in different regions due to the different geographical location, terrain, climate and human activities, etc. Both of the annual and seasonal mean AOD showed the same features that the biggest AOD value occurred in the third step and the least appeared in the first step. There were significant spatial differences of Yangtze River basin AOD. The significant increasing area was accounted for 17.54%, which mainly occurred in the first step, while the significant decreasing area was accounted for 5.23% and mainly appeared in the second and third step. Moreover, because of the effect, such as altitude, terrain and mountain barrier, etc, the area from the first step to the second step and the second step to the third step, the distribution of AOD was significantly greater than that of lower place. These results might be greatly helpful to learn the possible relationship between the regional climate change and the air pollution variation over the Yangtze River basin.