Abstract: Typical fog cases were simulated by the MM5 model in 2009 in Shanxi province. The results indicate that the simulated temperature at 2 m height is about 2 ℃ lower than the observed one; the simulated relative humidity is about 15% higher than the observed one; the simulated wind speed at 10 m height is about 0-2 m·s^-1 greater than the observed one. The forecast indexes of fog include three conditions in Shanxi province, namely, the liquid water content at 20 m height is from 0.13 g·kg^-1 to 0.60 g·kg^-1; there exists a temperature inversion layer between 20 m and 1500 m heights; the surface wind speed at 10 m height is less than 4 m·s^-1. A visibility forecast model is established by the daily mean visibility, relative humidity and air pollution index in Taiyuan. The forecast results of visibility by the MM5 and CAPPS are corrected using the observed data, and the revised forecast equation is developed. Two fog cases are forecasted using the revised equation, and it suggests that the model could be applied in Shanxi province.

Key words:  Visibility, Relative humidity, Liquid water content, Temperature inversion, Wind speed, Air pollution index