Fog Variation Tendency In Mountain Area Of West Hubei Province And The Difference In Atmospheric Boundary Layer Characteristics Between Mountain And Plain Radiation Fog

Climatic characteristics of mountain fog and mist in Xuan’en,west Hubei province are analyzed based on the meteorological data collected from observational station in the period1959-2009. Using the data from a simultaneous observation in Jingzhou and xuan’en in Decmber in2010, which represents Jianghan Plain and western Hubei mountain area, respectively, the characters of the temperature, relative humidity and wind of boundary layer has been analyed via a fog process in each area.It is shown that the average fog day is29annually and the annual fog days present a decreasing variation trend. The fog events occur in every month with the maximum frequency in winter,the next in autumn and the minimum in summer. It is also found that the annual mist days are generally increasing but there is an opposite tendency with annual fog days. The monthly average mist days in each month are between9and15with the maximum in December and the minimum in May. Furthermore, studies of the characteristics of meteorological elements point out that the annually average minimum air temperature is rising, the annual average relative humidity at08:00and the annual rainfall vary unobvious and the annual days of visibility at14:00greater than20km are decreasing. Results reveal that the unsymmetrical variation characteristics of fog and mist occurrence frequency probably have the correlation with the increasing aerosol in atmosphere.The radiation fog in Jingzhou of Jianghan Plain usually last longer than the one in Xuan’en, prone to thick fog and even serious thick fog which may bing large damage to human. By contrast, the fog in xuan’en lasts shorter and is not prone to serious thick fog.After analyzing the characters of a radiation fog in Jianghan Plain from28to29in December of2010, a strong temperature inversion structure occurs in the whole fog developing process, and the fog top is always in the upper part of the strong inversion layer. The inversion layer only be be lifted off the ground about50m in the mature and dissipated period of the fog, but it has not been lifted above the fog top. The paroxysmal developing of fog corresponds to the paroxysmal thickening of temperature inversion structure. Meanwhile radiation temperature inversion is layered with height, and temperature inversion intensity changes over time, ups and downs. The fog area is a low temperature area and a high relative humidity and specific humidity area. There is a good correspondence between the specific humidity curve and the temperature stratification curve. The maximum humidity gradient and temperature gradient appears near the fog top. After analyzing the radiation fog in western Hubei on December22th of2010, the results show that due to the special terrain environment in western Hubei,the surface wind speed is small,and it always less than3m/s when there is a fog. The fog of eastern Hubei is different from the one in Jianghan Plain due to the special terrain, which contributes the formation of fog owing to the contacting of low-altitude cloud.In the life time of fog there has no temperature inversion in the ground layer, but the lower layer’s temperature always decreases with height and the temperature inversion occures above it.