南岭山地浓雾的宏微观物理特征综合分析

COMPREHENSIVE ANALYSIS OF THE MACRO- AND MICRO-PHYSICAL CHARACTERISTICS OF DENSE FOG IN THE AREA SOUTH OF THE NANLING MOUNTAINS

关键词:  浓雾  能见度  天气系统  雾滴谱  雾含水量

Key words:  dense fog  visibility  weather system  fog drop spectrum  fog water content

摘要:

通过对南岭山地进行的雾野外观测资料以及数值试验的综合分析,得到了南岭山地浓雾和能见度的季节分布特征、雾滴谱微观特征与浓雾形成的物理概念图像。在秋末和冬春季节,南岭山地恶劣能见度出现的频率很高,能见度≤200m浓雾过程的出现频率平均为24.7%,最高可达41.8%;冬春季节南岭山地出现的雾是复杂的微物理过程、局地地形、水汽输送与影响天气系统等宏微观相互作用的结果,属于平流雾、爬坡雾类型,与辐射雾明显不同,局地山地抬升冷却凝结对雾的形成起重要的作用,迎风坡对雾的形成有利,在海拔较低的迎风坡也可能出现浓雾,从而导致低能见度;南岭山地的雾以小滴谱为主,数密度比城市雾小,小粒子段谱型基本呈下降趋势;在多个微观变量中,含水量与能见度的反相关性最好;雾含水量等微结构特征量的起伏变化,与雾体本身的微物理过程有关外,雾体随环境风的平移过程中,不规则的爬坡、翻越山坡的运动是造成雾体微结构不均匀、振荡起伏变化的重要原因。

Abstract:

Using the composite field observational data collected in the area south of the Nanling mountains and numerical modeling,the seasonal features of dense fog and visibility,fog drop spectrum and physical concept of fog forming have been analyzed.The occurring frequency of low visibility(≤200m) is very high with a mean of 24.7%,a maximum of 41.8% from the end of autumn to winter and next spring.The fog processes that occurred in the area south of the Nanling mountains in spring and winter resulted from the interactions of complicated micro-physical processes,the local terrain,water vapor transportation and the influencing weather system.The fog processes are arisen from advection or windward slope,which is much different from the radiation fog.Cooling condensation due to the air lifted by the local mountain plays an important role in fog formation.Windward slope of the mountain is favorable to the fog formation.Dense fog can occur at lower altitudes in the windward slope of mountain,resulting in the lower visibility.The fog is mainly of small-drop spectrum with smaller number-density than that of urban fog,and its drop spectrum has descending trend in the section of smaller diameter.The inverse relationship between fog water content and visibility is the best among several relationships of micro-variables.In addition to micro-physical processes of fog body itself,the motion of irregular climbing and crossing over hillside while the fog body is being transported by the wind are also important reasons for the fluctuation of micro-physical parameters such as fog water content.