江苏冬季霾日数的年代际变化与环流异常和区域增暖的可能联系

INTERDECADAL CHANGES OF WINTERTIME HAZY DAYS IN JIANGSU PROVINCE IN ASSOCIATION WITH CIRCULATION ANOMALIES AND REGIONAL WARMING TRENDS

近50年江苏冬季霾日数随时间线性增多,其距平变化在1970年代由负位相转变为正位相。这种变化可能与东亚气候突变有关。利用江苏气象站点资料和NCEP/NCAR再分析资料,结合江苏冬季霾日数的年代际变化特征,探讨其与年代际气候变化的联系。结果表明,在江苏冬季霾少发期(1961—1979年),500 h Pa高度场在欧亚中高纬地区表现为"正-负-正"的距平分布,即在乌拉尔山附近和阿留申群岛附近表现为正距平,而在贝加尔湖以东地区表现为负距平。这种"两脊一槽型"的分布有利于北方冷空气南下,冬季风较强,使江苏境内地面风速增大,有利于大气污染物扩散,同时大气净化次数有所增多,不利于霾天气发生。而在霾的多发期(1980—2010年),异常的大气环流型则相反。此外,江苏冬季霾日数对气温增暖存在可能的显著正响应。

An increasing linear trend is found in wintertime hazy days in Jiangsu province in the past 50 years. A transition from the negative to the positive phase is found around the end of 1970s in departures of wintertime hazy days from the 50-yr mean. Such a transition may be related to abrupt climate change in East Asia. In this paper, using the data of meteorological stations in Jiangsu and the NCEP/NCAR reanalysis, the feature of the decadal variability of wintertime hazy days in Jiangsu is investigated with discussions of its links with the interdecadal climate variations. Results indicated that during the period of low occurrences of wintertime hazy days in Jiangsu, the anomalous geopotential heights at 500 hPa in the mid-high latitudes from Europe to Asia are alternatively with positive-negative-positive centers, i.e., the positive anomalous geopotential heights are observed respectively in regions of Urals Mountains and around Aleutian Islands while the negative ones are found in regions around Lake Baikal. This ＂two ridge-one trough＂ pattern facilitates the southward migration of the cold air, intensifying the winter monsoon in East China, and henceforth leading to the evaporation and diffusion of atmospheric moisture and pollutants. This situation is believed not to be conducive to the occurrence of haze, especially in the period before 1979. However, in the period of 1980-2010, the circulation pattern looks opposite to those before 1979, which facilitates a weak winter monsoon, inducing more haze events in Jiangsu province in boreal winter. In addition, a possible relation is found between Jiangsu winter haze days and warming trends in this region as a result of the local response of the atmosphere to the thermal forcing due to warming trends there.