Local meteorological and synoptic characteristics of fogs formed over Incheon international airport in the west coast of Korea

Fogs observed over Incheon international airport (IIA) in the west coast of Korea from January 2002 to August 2006 are classified into categories of coastal fog, cold sea fog, and warm sea fog based on the areal extent of the fogs and the difference between the air temperature (T) and the SST, i. e., cold sea fog if TSST = T-SST > 0°C and warm sea fog if TSST < 0°C. The numbers of coastal, cold, and warm sea fog cases are 64, 26, and 9. Coastal fogs form most frequently in winter, while cold sea fogs occur mostly in summer and warm sea fogs are observed from January to May but not in November and December. On average the air gets colder by 1. 6°C during the three hours leading up to the coastal fog formation, and an additional cooling of 1.1°C occurs during the fog. The change in the dew point temperature (T_d) is minimal except during the fog (0.6°C). Decreases in T for the cold and warm sea fogs are relatively smaller. The average T_d is higher than SST during the cold sea fog periods but this T_d is more than 4°C higher than that for the corresponding non-fog days, suggesting that cold sea fogs be formed by the cooling of already humid air (i.e., T_d>SST). Increases of T_d are significant during the warm sea fog periods (1.4°C), implying that efficient moisture supply is essential to warm sea fog formation. Four major synoptic patterns are identified in association with the observed fogs. The most frequent is a north Pacific high that accounts for 38% of cases. Surface or upper inversions are present in 77%, 69%, and 81% of the fog periods for coastal, cold, and warm sea fogs, respectively.