Mechanisms of Local Explosive Development of a Radiation Fog Event

An explosive fog event was analysed which occurred in the coastal area of north- eastern Hebei Province( the Leting meteorological station as representative) and the Tianjin area from 21 to 22 December 2010,based on the observations obtained from the 255 m meteorological tower located in Tianjin,the NCEP reanalysis data with the spacial resolution of 1° × 1°,and the automatic meteorological monitoring data adjacent to the railway. The results indicated that: The explosive fog episode in Leting is the presence of the atmospheric moisture convergence near the shear line,along with the cold air inflow in the front of a short-wave trough,and longwave radiation cooling in the evening. The explosive thickened fog in Tianjin region is directly caused by invasion of a frontal weak cold air of the secondary cold front at lower atmosphere. In addition,the fog dissipation is due to strong cold air which is acompanied with the cold frontal passage. During the fog event,it's moist and clod in near surface layer,warm and dry in the upper boundary layer. In addition,the surface air temperature increases slightly prior to the fog intensification during the overall cooling tendency,which is an effective indicator of the explosive development of fog.