Meteorological data from automatic observation stations at different altitudes of Mount Jiuhua are used to analyze and compare the temporal and spatial distribution characteristics of fog,and the topographic effect as well.The results show that the average annual fog days are 19,82,145,110 days for flat land,low level,middle level and high level mountain areas,respectively,with increasing trends in flat land and decreasing trends in mountain areas.The temporal distribution of fog shows different characteristics in flat land and mountain areas.In flat land,fog occurred mainly in autumn and winter with peak value in October to January of next year,while in mountain areas,fog occurred mainly in spring and winter with peak value in March and low value in July.Fog mostly formed during 05:00-07:00 and disappeared during 08:00-10:00 in flat land and low level mountain area,while formed during 04:00-08:00 and disappeared during 09:00-11:00 in middle and high level mountain areas.The average and maximum fog lasting time is longer in middle level mountain area than it in other areas,and the shortest fog lasting time appeared to be 0.2 hour in high level mountain area.In the Mount Jiuhua,unsaturated air flows into the funnel-shaped area and cools down in ascending process,then the water vapor will reach saturation and the fog is formed thereby.Topographic temperature inversion provides stable stratification conditions,thus is significant for fog formation and duration.Convergence of wind field in mountain area also favors the fog formation and duration.