关键词: 雾日, 平流辐射雾, 锋面雾, 平流雾, 上海市区, 年平均风速, 上海城市, 月平均, 月份, 污染系数

Abstract: The fog of Shanghai can be classified into following four types: radiation fog(accounting for 44.8%), frontal fog (accounting for 24.8%), advection fog (accountingfor 17.6%), advection-radiation fog (accounting for 12.8%). As shown by the recordsduring recent 77 years, there are 43.5 foggy days per year on average. But its annualvariation is very remarabL. e.g., there are 107 foggy days in 1950, while only 17 foggydays in 1917; the former is more than six-fold as much as the latter. There are twofoggy seasons yearly: one occurs from October to December, and the other from Marchto May. Fogs rarely appear in summer (July and August). In this paper the re-gularity and causes of the seasonal and diurnal variation of fog in Shanghai are dis-cussed.The regional differences between urban districts of Shanghai and its suburbs areobvious. There are far more foggy days each year in its urban districts and the foggyseason there is also much longer. The distribution of foggy days is closely related to thefrequency of wind direction, wind velocity and coefficient of air pollution. Meteorologi-cal observations for a long period have proved that the fog in Shanghai urban districtsmay be formed in lower relative humidity (such as 67%), but in the suburbs of Shang-hai, only in very high relative humidity (98%-100%). Finally, it is pointed out thatthe fog of Shanghai is closely related to its geographical environment and the featuresof general circulation of atmosphere.