Surface Impacts of Springtime Extratropical Cyclones over the Bohai Sea and Yellow Sea, East Asia

Extratropical cyclones (ETCs) are active in spring over East Asia, and their surface impacts are crucial to northeast China, the Korean Peninsula, and Japan. In this study, a total of 215 continental ETCs crossing the Bohai Sea and Yellow Sea have been identified and tracked by applying an objective algorithm to the 850 hPa relative vorticity fields from the European Centre for Medium-range Weather Forecasts interim reanalysis (ERA-Interim) in March to May from 1979 to 2018. These ETCs were then classified into three groups by considering their geographical positions of cyclogenesis and cyclone tracks. Cluster 1 refers to the commonly named Mongolian cyclones that firstly travel southeastward and then recurve eastward. These ETCs are usually associated with a southward cold wave from Siberia and Mongolia resulting in decreasing temperature and reduced moisture uptake. The ETCs in cluster 2 mainly originate over the North China Plain, the leeside of the Loess Plateau, and Taihang Mountain, while ETCs in cluster 3 originate around southwest and central China. Greater moisture uptake occurred in the warmer region of these cyclones. The surface impacts of ETCs in clusters 2 and 3 were similar although their tracks were different. The passage of ETCs in clusters 2 and 3 across the Bohai Sea and Yellow Sea was associated with a period of lower tropospheric warming followed by a period of cooling. Extreme ETCs in all the three clusters could induce strong winds, and the risk of a storm surge was higher along the west and south coasts of the Bohai Sea and the west coast of the Korean Peninsula.