Numerical simulations on a dumpling fog event and analysis on the reasons of its engendering under the complicated topography

USA, the regular meteorological observational data in the Northeast Hemisphere and the observed data of the Automatic Monitoring Weather System on the Shanghai-Nanjing Expressway, in this paper, WRF V2.2 (The Weather Research and Forecasting Model for version 2.2), a non-static meso-scale numerical forecast model with high temporal and spatial resolving power, was used to simulate a typical dumpling fog weather event occurred on the Shanghai-Nanjing Expressway from 03:00 (BJT) to 09:00 (BJT), October 26th in 2007. In order to ascertain the influence of terrain and landforms on the engendering and dissipating of dumpling fog, the sensitivity tests on the terrain and the water system were carried out and a DEM (digital elevation model) in ArcGIS9.3, a software of geographic information system, combined with some topographical data was used to the spatial analysis of the dumpling engendering under the complicated geographic undergrounds. The results were showed as follows: The numerical simulations of a dumpling fog event indicated that: (1) The Zhenjiang section of the Shanghai-Nanjing Expressway bas been easy to appearing some dumpling fog weathers. The beneficial engendering conditions of a dumpling fog event were the stable atmospheric environment, the ground surface radiation cooling at night, and the cooling of the warm and wet flow from the southern regions moved through the cooler ground surface. (2) When two branches of airflows from the different directions of the north and south converged in the western part of the Expressway, it was favorable to the standstill of wet air and aerosol particles and it also was one of the main reasons for the developing and maintaining of the dumpling fog weather. (3) The dumpling fog dissipated rapidly when short-wave radiation warmed the air closed to the ground after sunrise. (4) The sensitivity tests of terrain and water system displayed that the distribution of terrains and landforms in the fog area were sensitive to the formation of dumpling fog. The undulating terrain and the environmental water system had certain effect on the engendering of dumpling weathers.