福建近44年雾日趋势变化特征及可能影响因素

The Trend Variation Feature of Fog Days in Fujian Province for Recent 44 Years

应用1961—2004年福建省50个气象站逐月大雾及浓雾日数资料,分析了全省大雾日数及浓雾日数的年、季分布特点、长期变化趋势、年代际变化特征以及可能的影响因素。结果表明:全省年、季雾日数分布均表现为中部及三明西部的多雾区,沿海及南部地区的少雾区,而多雾区中浓雾所占的比率达30%以上;全省年、季大雾日数大部分地区表现为明显的减少趋势,仅在龙岩西部呈增加趋势,而浓雾的减少趋势不如大雾;年、季雾日数具有明显的年代际变化特征,年、季雾日数在20世纪80年代中期左右转为明显偏少期,之前则为明显的偏多期。文中还重点分析了6个代表站大雾与浓雾的趋势与月际分布特征。进一步研究指出,年雾日数与年平均气温有较好的负相关关系,而与年平均相对湿度有很好的正相关关系,同时与森林覆盖率的变化有一定关系。

The monthly data of fog （visibility less than 1000 m） and dense fog （visibility less than 500 m） from 50 meteorological stations in Fujian Province in the period of 1961-2004 are used to analyze the annual and seasonal distribution feature, the long term trend variation, the annual and decadal variation and possible influence factors etc. The results show that the regions where annual and seasonal fog occurs frequently are in the central and western Sanming, while few occurrences are in the coast and the south of Fujian, the same is dense fog. Among the more fog regions, the number of annual fog days is more than 80, some exceed 100 days. In less fog regions it is less than 20 days. More than 30 % of fog days in more fog areas are dense fog, some areas such as the southern Nanping it can even pass 50 %. Dense fog seldom occurs in the coast. Fog occurs frequently during autumn and winter （October to next February） in inland and in spring in the coast areas. In summer, fog events are not prone happening. The time which dense fog appears often is in October to next February. The tendency of annual and seasonal fog days significantly decreases in large parts of Fujian with the tendency coefficients above 99.9 % confidence level for 30 stations, and only in western Longyan and parts of the coast the tendency increases. For dense fog, the decreasing tendency is less than that of fog, there is nearly no change in the tendency in the south and the middle coast in Fujian, only in the middle inland the tendency has significant decrease. Analysis is focused on decadal average numbers of dense fog and its deviation coefficient. It is pointed out that though the dense fog days have a small decrease in 1990s but its deviation coefficient is the biggest, therefore the dangerous of dense fog increases while the predictability is difficult. The annual and seasonal fog days represent significant decadal variability. The annual fog days are below the normal after the mid 1980s, before which it is above the normal. Special analysis is given to 6 representative stations for the tendency and monthly variable rule of fog and dense fog. Furthermore studies of the reasons for the decrease of fog point out that the fog days have good negative relation with annual average temperature, and good positive one with relative humidity. The remarkable jump points for the three are in the mid 1980s. After that time the temperature increases faster, while relative humidity reduces remarkably and the numbers of fog decrease too. It still has a certain relationship with the dimension of forest. But due to the limited data, it now has some uncertainties.