Characteristics of Heavy Fog in Dalian

Two heavy-fog processes occurred in February and April, 2007 of Dalian and its coastal area are analyzed using the sounding data from GTS1 digital radiosonde, conventional observation data, and NCEP/NCAR global 1°×1°reanalysis data. The diagnostic analysis of environment and its dynamic and thermodynamic effects on the heavy fog indicates that high-level zonal warm and dry airflow at high latitude and southwest warm and moist airflow in mid-lower troposphere supply water vapor and wind for the formation of fog. The existence of air steady layer at lower-layer and the superposition between fog layer and the warm, dry air are of benefit to the maintenance of heavy fog.Furthermore, sea surface temperature on Yellow Sea and Bohai Sea induces the further warming and transformation of surface cold high in winter, which is favorable to the formation and development of radiation fog. As a result, the warm air-mass cools and condenses in spring, which causes maintenance of the advection cooling fog. And the north wind followed by the southeast moving of cold convection is the dynamic factor to dissipate the persistent heavy fog.