Characteristics and prediction of heavy fog weather in Changzhi City

The background of fog climate which horizontal visibility less than 1km in Changzhi City,was explored by researching the geographical distribution of the fog and its yearly,monthly and daily changes from 1971 to 2004.According to the physical mechanism of formation of fog,authors analyzed wind field,humidity field,temperature field and cooling condition,then integrated fog prediction model.With the analysis of 98 examples of fog,we classified the dense fog-forming main 500 hPa high-altitude weather situation(zonal circulation pattern,weak northwest flow pattern,after the trough northwest flow pattern,weak internal high pattern) and the main ground pressure field(weak high pressure field,both pressure field,saddle field).The results can give a reference to early warning and forecast of the heavy fog weather.