Mechanism Analysis Of Propagation Of Regional Heavy Fog In Eastern China During Winter

Based on normal observation data and NCEP reanalysis data,Eastern China regional dense fog in winter of 2015-2018 are analyzed with focus on propagation mechanism.On this basis,nine prediction factors suitable for regional fog prediction are summarized,and the effect of WRF output on fog prediction is evaluated.The main conclusions are as follows:1.This article summarizes and classifies the regional dense fog in Eastern China.Eastern China regional dense fog can be classified into Huabei regional dense fog,Jianghuai regional dense fog and H-J regional dense fog;the circulation situation can be divided into high-pressure ridge type and uniform pressure field type.2.The propagation mechanism of Eastern China regional dense fog in winter was analyzed.(1)The change of circulation situation is the direct factor leading to the rapid development and spread of regional dense fog.Uniform pressure field type is beneficial to maintain the strong fog and at the same time restricts its propagation;High-pressure ridge type is beneficial to produce large-scale strong temperature inversion areas.(2)Temperature inversion areas and water vapor conditions are indispensable for the formation of regional dense fog.Temperature inversion areas can prevent evacuation of water vapor in horizontal and vertical directions;water vapor conditions guarantee sufficient water vapor condensation to maintain fog development and propagation.(3)Topographic conditions are an important factor affecting the occurrence,development and spread of regional dense fog.3.Nine forecast factors suitable for fog area prediction of regional dense fog are summarized.Nine forecast factors are circulation situation,ground wind speed,T-lnP radiosonde observations,975hPa-ground temperature difference,1000 hPa temperature advection,temperature variation,ground relative humidity,1000 hPa vapor flux and topographic conditions.4.Simulates a regional dense fog case by WRF model and evaluates its fog area simulation effect.It is accurate to judge the fog area by the relative humidity of 2m and the wind speed of 10 m from the WRF model,which is basically consistent with the actual fog area.But the simulation results in the near ground layer are not good,and the simulation of relative humidity is higher than the actual situation,the simulation of fog area by LWC(Liquid water content)is not ideal too.