Study On The Characteristics Of Temporal And Spatial Distribution And Numerical Simulations Of Fog On The Jiangsu Coastal Expressway

Fog is one of the most serious meteorological disasters in highway traffic, the occurrence of fog on the coastal highway characteristics at home and abroad and the researches on the mechanism of the fogging are reported. Based on the observed data of the traffic meteorological stations on the Coastal Expressway of Jiangsu during June in 2012 to May in 2014, in this paper, the temporal and spatial occurrence pattern was analyzed according to the classification of the visibility values and main physical formation mechanisms in fog occurrence processes statistically and the causes brought about the difference of these temporal and spatial pattern was discussed. One typical radiation fog event and one typical advection fog event were filtrated, WRF3.4.1 mode was used to carry out numerical simulation test, respectively from the perspective of different physical quantities field, analyzed the formation mechanism of two types of fog, and points out two kinds of fog in the similarities and differences in the process of generation and dissipation. Research on highway fog monitoring and early warning and forecasting has important theoretical significance and practical value.Statistical analysis of different visibility and different type fog on the Coastal Expressway of Jiangsu, the results showed as follows:(1) The daily and annual variations pattern of the thick fog, dense fog, heavy fog and strong fog was similar on the Coastal Expressway of Jiangsu. All of the fog events occurred during 9 pm in a day to 5 am of the next day and disappeared from 5 am to 9 am in a 24 hour cycle. The lasting duration from long to short is followed by strong fog, heavy fog, dense fog and thick fog. Autumn and winter in a year were the seasons of high occurrence frequency for thick fog, dense fog and heavy fog, and the strong fog often occurred in summer. (2) The thick fog, dense fog and the heavy fog often appeared in the north part of the expressway and the strong fog occurred in the middle part of the expressway with high occurrence frequencies. (3) In a day, the advection fog had the widest range in the appearing and disappearing times, the occurrence of the frontal fog was in the most narrow appearing time range and evaporation fog had a shortest disappearing scope. The mixed fog lasted the longest time, the frontal fog had the shortest duration. The multiple season of the radiation fog was autumn and the advection fog had a larger occurrence probability in winter. (4) The radiation fogs were prone to the north part of expressway, the advection fog often occurs in the south part.The Weather Research and Forecasting Model for Version3.4.1 (WRF3.4.1) was used to the simulations and diagnostic analysis of a radiation fog event during 14th to 15th, September in 2013. The results showed as follows:(1) Before the radiation fog event, a lot of moist air flocked to the land under the influence of east air flow, was the main water vapor sources of the fog. (2) A weak wind present before the fog event and during the fog process provided favorable dynamic conditions for engendering fog. (3) The role of radiation cooling induced the outbreak of this radiation fog. Enhanced surface long-wave radiation flux, directly prompting the temperature drops rapidly before the fog process, provided favorable thermal conditions for engendering fog. The inversion layer on the top of the fog played an important role for maintaining. Inversion layer disappeared, radiation fog disappeared.The Weather Research and Forecasting Model for Version 3.4.1(WRF3.4.1) was used to the simulation one advection fog event during 25th to 26th, February in 2013. The result of diagnostic analysis showed as follows:(1) The advection fog is formed by the translation of sea fog. After the sea fog formation, a lot of moist air flocked to the land under the influence of southeast air flow, provided favorable water vapor condition for the occurrence and development of the advection fog. (2) Before and during the fog event, continuous and stable southeast wind provided the necessary dynamic conditions of the generate and maintain of the advection fog. After the wind direction into the west wind, the advection fog dissipated. (3) The atmospheric thermal stability was higher in this advection fog process, thermal conditions was in favour of forming the advection fog event. While the stable inversion layer exists, visibility reduced gradually in surface layer. The disappearance of the inversion layer disappeared in the mist in surface layer.Similarities and differences in two kind of fog dissipation mechanism was showed as followed:(1) The similarities were as followed:Water vapor sources are both from the sea and the stability of the inversion structure both played an important role in generating, maintaining and evanishing. (2) The differences were as followed:Horizontal wind speed was weak before the radiation fog process, with convergence ascending motioning in the air. Horizontal wind speed was weak before the advection fog, with weakly vertical sinking motioning in the air. The principal cause of the radiation fog formation was cooling; the main reason was the humidifying during the advection fog.