长江三角洲地区近30年非雾天能见度特征分析

Analysis of the Visibility Change in the Yangtze River Delta Region in Recent 30 Years

利用地面能见度观测数据和中分辨率成像光谱仪(简称M(ODIS)所提供的气溶胶光学厚度(Aerosol Optical Depth,AOD)资料,分析了中国长江三角洲地区近30年的能见度变化特征。结果表明,该地区1980—2009年能见度年均值为19.5±1.8km,其中最高值为21.9km,在1984年,最低值为16.1km在2007年。近30年能见度呈下降趋势,平均年递减率为-0.20±0.013km/a,近几年能见度趋于稳定。该地区能见度:夏季能见度最好,秋、春季次之,冬季最差;沿海地区能见度好于内陆地区,沿江(河)两岸能见度较差;沿江(河、海)地区能见度的下降速度大于其他地区,在浙江东南部沿海地区尤为明显。利用EOF方法分析长三角地区能见度,结果表明第一模态的特征向量均为正值,说明全区能见度均呈下降趋势。利用MO-DIS AOD数据分析区域性及长期能见度变化趋势与利用地面观测数据方法分析结论相一致。

The visibility change was analyzed with the observations from ground stations and the aerosol optical depth （AOD） data from Moderate-resolution Imaging Spectroradiometer （MODIS） in the Yangtze River Delta region in recent 30 years. It shows that the annual mean visibility was 19.5 ±1.8 km during 1980--2009 with a maximum value of 21.9 km in 1984 and a minimum value of 16.1 km in 2007. The visi- bility has a downward trend in recent 30 years at a rate of -0.20±0. 013 km/a and tends to become stable in the last few years. The visibility changes with the seasons in this region which is the highest in summer, followed by autumn and spring and the lowest in winter; the visibility in the coastal areas is higher than that in inland, and it is lower along the rivers; the decreasing rate along the rivers and the coast areas is higher, especially in the southeastern Zhejiang. The EOF method was used to analyze the visibility of the Yangtze River Delta region. The result shows that the eigenvectors of the first mode are all positive, indi- cating the decreasing trend of the visibility in the whole region. The analysis on the regional and long-term visibility change made by the MODIS AOD data coincides with that by the ground station observations.