The Burst Reinforcement Process And The Numerical Simulation Of The Twice Heavy Fog After The Rain

The general situation of the twice heavy fog after the rain occurred on 21 December was studied based on the data collected from the fog observation experiment during the winter of 2015 at Nanjing University of Information Science and Technology. Study the characteristics and the causes of the burst reinforcement especially, on the basis of analysis about the weather background and boundary layer structure of the typical fog process. The result shows that:The high humidity environment at ground and surface layer after rain provides sufficient moisture for the formation of the fog, the stable weather stratification controlled by the winter cold high-pressure in Nanjing, and radiation cooling at night,which are highly favorable to the generation of the radiation fog. The burst reinforcement of the fog mainly is related with the cooling and wetting. The strong cooling caused by the enhancement of surface upward long wave radiation owing to the decrease sharply at the sunny night, the increased moisture near surface caused by the strong evaporation after sunrise from the ground and the frost attached to the plants, which all can directly give rise to the burst reinforcement of the fog. It is the key to the burst reinforcement of the fog that is the formation of the strong inversion layer, which is easy to accumulate the moisture near the ground and to prevent it spread upward. The reinforcement of the ultra-low-level jet which occurred at 100?150 meters height of the wind profile at the inversion lid, will help speed up the decline and enhancement of the inversion layer.In this study, a preliminary numerical simulation of this case was conducted by using a one-dimensional model of radiation fog named PAFOG. Comparison between prediction and observation was made about a typical radiation fog event.The result shows that: The visibility was simulated accurately at most, among the ground basic meteorological elements. The temperature could simulate the changing trends accurately, but the prediction of the lowest temperature is on the high side, and the prediction of the highest temperature is on the low side. The simulation results of the relative humidity were almost consistent with the observed result among the fog event, but the error was larger after the fog dissipation.The results on the sensitivity test showed that cooling and humidification would promote the thickening of the fog.The change of cloud cover has a great influence on the varying trend of visibility.