황해 저층냉수에 기인한 표층 수온 냉각이 한반도 연안 기상요소에 미치는 영향

Abstract

Despite strong summer stratification in the Yellow Sea (YS), it is often observed that sea surface temperature (SST) decreases sharply due to a vertical mixing between warm surface water and cold subsurface water that originated from the Yellow Sea Bottom Cold Water (YSBCW). SST is one of the most important factors in controlling heat and water vapor exchange across the air-sea interface and thus influences atmospheric phenomena significantly, including synoptic weather conditions. In this study, we examine and quantify how the SST reduction associated with the YSBCW affects the weather conditions around the Korea Peninsula, using a coupled modeling system for ocean-atmosphere interaction. A set of comparative experiments are performed during Typhoon Muifa: 1) uncoupled atmosphere model with a constant SST taken as the initial value from Real Time Global (RTG), 2) uncoupled atmosphere model with daily SST prescribed from RTG, and coupled ocean-atmosphere with different initial of ocean model from 3) global Hybrid Coordinate Ocean Model (HYCOM) and 4) Navy Coastal Ocean Model (NCOM). Buoy observations showed an abnormal SST cooling during the typhoon passage; however, the prescribed SST in the atmosphere model (i.e., uncoupled experiments) did not fully resolve the sharp fluctuating feature generated by Muifa. As a result, the uncoupled model results do not predict the abrupt changes of SAT in response to the typhoon-induced SST cooling. On the other hand, the ocean-atmosphere coupled model indicates a key role of the YSBCW in determining the sea surface cooling during the typhoon passage, and demonstrates that the oceanic cooling affects significantly the weather predictions around the Korean Peninsula. The SST reduction cools the low-level atmosphere, which leads to the convergence in moisture flux over the colder ocean, providing a favorable condition for the formation and evolution of sea fog. In addition, the sea surface cooling stabilizes the atmospheric boundary layer that promotes the condensation of water vapor within the low-level and then suppresses vertical mixing, which inhibits the dissipation of sea fog. These results suggest that the oceanic cooling through air-sea coupling plays an important role in weather conditions around the Korean Peninsula