Analysis On The Difference Of Fog Days Formation In Different Regional Climate Conditions In China

Fog is a severe weather hazard that greatly influences traffic and daily life with potentially heavy economic loss.In this paper,the temporal and spatial characteristics of fog days in winter were analyzed,which baesd to define fog areas,and we try to analyze respectively the influence of the differences in the climate conditions of three fog areas for the physical mechanism of fog days,and discuss how the differences of regional climate conditions influence the formation of fog days in winter.The main conclusions can be drawn as follows:(1)The distribution of fog days in China is characterized by a large number of southeastern parts and a small number of northwest parts.There is a certain similarity between the average annual values of the large standard deviations of fog days and the winter fog days.The interdecadal variation in the number of fog days generally shows a trend of decrease in fluctuations.Fog has a high frequency in the winter(November to February).Taking the winter fog days as our research object,it was found that the distribution of fog days in winter is characterized by a large number of southeastern parts and a small number of northwest parts,and the fog days in winter are concentrated in the southwest China,southern China,and North China.Analyzing the seasonal changes in the winter fog days,the fog days were the most in December and were the least in February.To explore the climate background with many years of winter fog,we found that the circulation system that affects the amount of winter fog days in the eastern part of China is mainly the mid-latitude system.When the number of fog days in winter is larger,the circulation is weaker in winter,and stronger,on the contrary.When the the number of fog days in winter is larger,the relative humidity on the ground is relatively high,indicating that the air with high relative humidity and sufficient water vapor is more likely to form fog under the favorable circulation field.(2)According to the characteristics of winter fog days,we defined three fog areas:Southwest,North China,and South China.There are significant differences in the inter-annual variations of fog days in the three fog areas.From the water vapor conditions,atmospheric stability and circulation background field,the influence of different climatic conditions in the three fog areas on the local fog formation mechanism was analyzed.The formation of the winter fog over southwestern China is less affected by the water vapor transport,while more affected by the atmospheric stability and the southward cold air.The formation of winter fog days over northern China is affected by water vapor transport,and when water vapor transports more north and convective instability occurs over Middle and lower Yangtze River,the fog over northern China occurs more frequently.While,the formation and maintenance of winter fog days over southern China is also influenced by vapor transport,and when water vapor transports more south,the fog over souththern China occurs more frequently.In terms of the atmospheric circulation systems,the winter fog days are mainly affected by the deepening high pressure ridge,east of the Balkhash Lake,the weakening of East Asia trough and Siberian High,and the weakening of the Siberian High,respectively,over southwestern China,northern China,and southern China.(3)The formation of fog is mainly determined by the two factors of air moisture content and cooling.The interannual variation trend of ground moisture in China and its relationship with winter fog days were discussed initially.In terms of specific humidity,the distribution of specific humidity in China is characterized by a decrease from low latitude to high latitude.From the long-term trend of change,the trend of the number of fog days and the trend of specific humidity are basically the same and closely related.When the surface specific humidity increases,the winter fog days increase in North China and South China,while decrease in southwest China.The analysis of the temperature field shows that the temperature is decreasing from south to north.Except for the weakening trend of the temperature in the eastern part of Tibet and the western part of Yunnan,the surface temperature in most parts of the country showed an obvious upward trend,and the degree of increase generally increased with latitude.When the winter surface temperature increases,the number of winter fog days decreases in the southwest,and increases in the North China and South China regions.