Abstract:Using the minutely data including visibility, relative humidity, temperature and wind speed of 36 automatic weather stations along the Yangtze River in Jiangsu Province during 2010-2013, the characte ristics of river fogs are analyzed. The results show that river fog mainly occurs in June, November and January, formed from 19:00 BT to the next 07:00 BT, during which the fog is the thickest in 02:00-04:00 BT and gets to end from 06:00 BT to 12:00 BT, so the fog duration is 3-9 h. When fog occurs, relative humidity is 85% or higher, temperature is 5-19℃ in spring, 18-26℃ in summer, 7-23℃ in autumn and 0-11℃ in winter. As for the wind speed, it is below 5 m·s-1 in spring, summer, autumn, and about 6 m·s-1 in winter. Specifically, the fog tends to occur with the wind direction of NNE-E and wind speed 1-2 m·s-1 in spring, the wind direction of NNE-ESE and wind speed 0.3-1 m·s-1 in summer, the wind direction of NNE-NE and E-ESE, wind speed 0.3-2 m·s-1 in autumn, and the wind direction of NNE-NE and WNW, wind speed 1-2 m·s-1 in winter. In addition, by analyzing the visibility changes of the first station in the fog, we found that there are obvious “trunk like” characteristics before river fogs develop. Such features could provide the basis for the operation of early warning and forecasting of river fogs.