上海雾的气候变化特征及城市化对雾影响的初步研究

A Preliminary Study on the Climatic Change of Fog Frequency in Shanghai and the Impact of Urbanization

利用1961—2008年(48 a)的常规气象观测资料,首先分析了上海地区雾的变化规律,其中包括上海地区各站各时期年平均雾日数时空分布、月际变化、季节变化和年际变化等特征。在此基础上选取城区、城郊和远郊的代表站,对比分析了上海地区雾的特征,初步讨论了雾的城市化效应成因,研究了城市化进程与雾长期变化趋势之间的关系。结果表明:(1)从20世纪80年代开始,上海地区年雾日数均呈现出明显的减少趋势,其中徐家汇和闵行的减少趋势最为明显,20世纪90年代开始郊区雾日数比市区多,郊区与市区雾日数的差距主要体现在冬季;(2)城市化造成的"干岛"和"热岛"效应与上海地区雾的长期变化趋势存在明显联系,城市化程度很高的城区和城郊地区近10年中"干岛"和"热岛"对雾形成的抑制作用已经大于城市化所带来的凝结核增多对雾形成的有利影响。

Based on the observation of the meteorological data from 1961 to 2008(48 a),the fog changing regularity around Shanghai was analyzed,including spatial-temporal characteristics,inter-monthly variations,seasonal variations and inter-annual variations of average annual fog events in various periods at meteorological stations in Shanghai.Based on the above data,several typical representative stations were selected from the meteorological stations of urban areas,suburbs and outer suburbs.The fog characteristics of Shanghai area were analyzed by a comparative analysis method.A preliminary discussion on the urbanization effect of fog was made.The observational research on the relationship of urbanization process with long-term trends of fog variation shows that:(1) It is obvious that the annual fog frequency of Shanghai had a distinct descending tendency,especially in Minhang and Xujiahui area from the 1980s.From the 1990s to present,the fog events occurring in suburbs became more frequent than that in urban,especially in winter.(2) In Shanghai area there was a close relationship between the long-term trend of fog frequency variation and the effects of'urban dry island'and'urban heat island'caused by urbanization.In the last ten years,the restraining fog formation effects of the two islands exceeded the facilitating fog formation effect of increasing condensation nuclei brought by urbanization because of the high urbanization both in downtown and suburbs.