The Physical Process Of Genesis And Dissipation And The Characteristics Of Burst Reinforcement On Typical Winter Fog In Nanjing

Synoptic background, and the physical characteristics of genesis and dissipation on radiation fog, radiation-advection fog and frontal fog are analyzed based on the data obtained by means of comprehensive observation in the ground track field of Nanjing university of information science & technology during the winter of 2006 and 2007. In addition, the characteristics of burst reinforcement are analyzed on the three dense fog processes (time: December 12^th,14^th and 24^th-27^th), and some reasons about burst reinforcement of fogs are discussed. The result shows that:There exist inversion layer structure during the generation and development of the three kinds of fogs, which are obviously different from the radiation fogs once studied about temperature and humidity structure. Generational and developmental mechanism, and dissipated causation are different among the three kinds of fogs. Radiation fog and radiation-advection fog are both formed on the condition of cloudless sky and nighttime radiative cooling. Frontal fog with light rain is formed and maintained under the frontal weather. Radiation fog provided with double deck fog, exists obvious diurnal variations, and often dissipates after sunrise. For December 24-27 there occurred a heavy fog with rare characteristics, namely high fog top, thick fog layer and long persistence because of compositive function of the deep temperature inversion, stable stratification at the boundary layer, appropriate wind condition and continuous warm- humid airflow. It dissipated on condition of gale and cooling because of cold air from north southwardly moving. Frontal fog was generated at the conjunction of cold and warm air. Warm and wet raindrops upper dropped into cold and dry air lower, vaporized to make air supersaturated, so as to coagulate into fog droplets. Frontal fog was weared off and dissipated with fortified cold air and turbulent.Visibility fell sharply with short time (in 30 minutes), Fog droplet number concentration, water content and droplet size increased markedly, and fog droplets spectrum became broader. Some causes were revealed that sharp drop of temperature because of radiant reinforcement of long wave or cold advection of nether layer, increase of humidity because of water vaporization of surface after sunrise or enhancement of southwest humid advection with turbulent mixing can make fog reinforce eruptively.