Marine boundary layer structure during sea fog events off the west coast of the Korean Peninsula

Sea fog is a significant weather phenomenon that usually occurs below a marine boundary layer. Many researches on marine boundary layer have been carried out over the Californian coast and mid-latitude region (Norris, 1998, 11, J. Climate, 383-403). Marine boundary layer in the subtropical oceanic region off the California coast is well-defined due to the subsidence induced by North Pacific anticyclone. Cold advection by northwesterly winds, then, almost persistently leads to the formation of stratocumulus clouds over this region. On the other hands, marine boundary layer is shallow in mid-latitude region and is formed mainly due to warm advection by southerly winds rather than the subsidence induced by an anticyclone.

Incheon International Airport (hereafter IIA) is located in the west coast of the Korean Peninsula in mid-latitude region and warm air moves to this region frequently in summer by monsoonal circulation. This study examines the structure of marine boundary layer in this region and intends to characterize the marine boundary layer structure during sea fog events.

Sea fog identification is made with visibility and relative humidity data at IIA, a buoy (~60 km off the coast) and an island (~ 230 km to the west of IIA in the Yellow Sea). In addition, rawinsonde soundings from the island at 00 UTC and 12 UTC are analyzed. Only the cases when the temperature difference is greater than 0.5 oC at the inversion that occurs below 800 mb altitude are considered as inversion cases. According to this criterion, there are 1967 inversion soundings out of the total 2833 soundings. The inversion base height is the lowest in May and the highest in December and the inversion layer is thicker in summer than in winter. Eighty two percent of the vertical soundings observed during sea fog events have an inversion. Moreover, inversion base height is lower in the presence of sea fogs and it seems to be a determining factor of the areal coverage of sea fogs. That is, the marine boundary layer is the lowest when sea fogs extend over to the island while it is the highest when sea fogs are limited only to IIA and nearby region. More in depth analysis of meteorological and synoptic conditions that are susceptible to marine boundary layer thinning and sea fog formation will be presented at the conference.