Impact of SST on the development of the cold surges over East Asia

This study investigates synoptic characteristics of the cold surges over South Korea during winter season (December-February). A total of 61 cold events are selected by quantile regression analysis using daily mean temperature observations from 11 surface stations for 38 years(1981–2018). Composite analyses reveal that a synoptic-scale cyclone developing over the northern Japan is a key feature that significantly contribute to the enhancement of cold advection by increasing pressure gradient over the Korean peninsula. Enhanced sensible and latent heat fluxes are observed over the southern ocean of Korea and Japan during the cold surges due to increased temperature and humidity differences between the lower atmosphere and ocean surface. These fluxes are transported toward the center of the surface cyclone and help the development of the surface cyclone by inducing positive PV in the lower atmosphere. These processes make a positive feedback loop that amplifies strength of the cold surge. To examine how sea surface temperature (SST) affects the strength of cold surge, we categorize the cold surges into warm, normal and cold SST cases. As a result, stronger and more pronounced cyclones are observed in cases of warm SST. Thus, the positive feedback process particularly enhanced when SST is warmer in the early winter.