The Distribution and Seasonal Variations of Fog in China
中国雾区的分布及其季节变化

The geographic distribution features and monthly/yearly variation rule of foggy days in China are analyzed based on the monthly mean fog data collected from 604 observational stations for the period 1961-2000. It is shown that there are six fog regions in China: the middle reaches of the Yangtze River, coastal area, Yunnan-Guizhou Plateau, eastern Gansu-western Shaanxi, Huaihe River Valley, Tianshan mountainous area and northern Xinjiang. On the whole the yearly variation trend of foggy days is descending, it is especially obviously after the 1980s. The areas where the foggy days have obvious tendency present a southwest-northeast trend. The rising trend regions alternate with descending trend regions, having a SE-NW directional wave structure formed. In general, the number of foggy days in autumn and winter is larger than in spring and summer over most fog districts. The monthly variation curves of foggy days are bimodal in the shore area of the Yellow Sea and northern Xinjiang, and unimodal in other regions.