Numerical Simulation Of Continuous Fog-haze Process And Visibility Parameterization Based On WRF-CHEM Model

The comprehensive field experiments of fog have been conducted in Jingzhou, Hubei in December,2010. The3days continuous radiation fogs were analyzed by using the achieved observational data. By analyzing weather situation and evolution, findings show that haze exists in fog process. The reason why coexistence of fog and haze and their mutual transformation can make the visibility basic maintain under10km is that air pollution is heavy in Jingzhou. Based on WRF-CHEM model, numerical simulation comparative tests will be carried out with and without atmospheric chemistry for the3days continuous fog-haze process. On this basis, the dynamic factors, microphysical characteristics of radiation fog and the atmospheric composition distribution characteristics of fog areas will be investigated. In addition, this article will compare and contrast the visibility parameterization scheme to improve the visibility parameterization scheme and evaluate its estimated result. The results show that:Conditions of abundant vapor and stable atmospheric stratification result in the fog-haze process. The coming of north cold air leads to the dissipation of fog and haze. The radiative scheme, boundary layer scheme and surface layer scheme is sensitive to the simulation of radiation fog. Compared with other schemes, it is better to choose CAM scheme for both longwave and shortwave radiation, and to choose QNSE scheme for the boundary layer and the near-surface layer because this combination could be a better scheme to simulate the evolution of Jingzhou radiation fog. In the test of atmospheric chemistry process, it has been found out that the simulation of fog area,2m air temperature, relative humidity and surface wind speed are more consistent with the observation data than the simulation of the test without atmospheric chemistry process. In formation and development stage of radiation fog, the fog area is in uneven distribution, and water vapor divergence and smaller wind speed are conducive to the development of radiation fog. In the early of mature stage, the top of fog layer and inversion layer is straight. Late in the mature stage, the vapor transport of low altitude to high altitude leads to the increase of thickness of fog layer, and the top of fog increases with the top of inversion layer uplifting. In the dissipation stage of radiation fog, it shows characteristics that the air distribution of ground layer is uneven, and the sinking airflow from the fog top to ground results that the fog layer will dissipate first.The distribution of fog area has a good consistency with the distribution of PMio, PM2.5fine particles, SO2and NO2. In addition to considering the extinction of cloud precipitation particles, it also needs to consider the extinction of air pollutants and aerosols for the extinction factor of atmospheric visibility. Fog-water is the largest extinction factor in radiation fog formative stage. When it is sunny or the situation that fog and haze coexists, aerosol (PM2.5and PM10) is the most obvious factor for extinction. The estimated visibility of Vis-Aerosol scheme is more consistent with the observed data than Vis-RH scheme. Vis-LWC and Vis-Qnfog parameterization scheme is only applicable to diagnose visibility of radiation fog, but not to diagnose the change trend of fog-haze process.The improved visibility parameterization scheme is superior to the Vis-RH and Vis-LWC scheme for the simulation of the visibility trend in the process of fog and haze. In the fog and haze coexisting stage, the mean absolute error of estimated visibility is2.41km. In the stage of radiation fog, the mean absolute error is0.62km. The absolute error is3.64km when weather is sunny.