Abstract: Based on the visibility and relative humidity data at 36 weather stations from 1980 to 2011 in Chongqing, the climatic characteristics of fog were analyzed. Typical heavy fog events were selected, and the circulation situation of radiation fog and rainy fog, vertical structure of temperature, humidity and wind were discussed using the NCEP reanalysis data with the resolution of 1°×1°and the L band radar data. The results indicate that the number of fog events is larger in the west than in the east of Chongqing, and the fog weather usually appears from October to February of next year. Annual mean number of fog days is in a significant decreasing trend in the early of this century, and an abrupt change occurs in 2002. There is high pressure ridge at 500 hPa in areas of Central Asia and Qinghai-Tibet plateau when radiation fog takes place, and Chongqing is located in the pressure equalization field inside the high atmosphere pressure and cold front reaches the South China. However, there is low pressure trough at 500 hPa in Qinghai-Tibet plateau when rainy fog takes place, and the center of surface cold high pressure is located in the north of China, which makes the weak cold air penetrating through Daba Mountain into Chongqing from the northeast. The vertical structures of temperature, humidity and wind speed for fogs of two types differ each other. Inversion temperature of radiation fog near the ground layer is obviously stronger than that of rainy fog. The vertical structure of humidity for radiation fog is dry in the upper layer and wet in the lower layer, while that of rainy fog is deep wet layer. At the same time, wind speed near the ground is slow, while the wind speed in each layer is faster during rainy fog than during radiation fog.

Key words: font-family: "Times New Roman", mso-ansi-language: EN-US, mso-fareast-language: ZH-CN, mso-bidi-language: AR-SA, Radiation fog')">mso-fareast-font-family: 宋体">Radiation fog, Rainy fog, Composite analysis