Impact of upper-ocean thermal structure on the intensity of Korean peninsular landfall typhoons

The roles of oceanic factors in the intensity of typhoons which made landfall on the Korean peninsula (KP) are investigated using various meteorological and oceanic measurements and the best track data. Special attention is given an investigation of upper-ocean thermal conditions necessary for becoming the most destructive typhoons on the KP. Based on hydrographic measurements and ocean modeling results, the subsurface thermal structure (STS) along the track of the KP-landfall typhoons reveals two distinct features: the deep subsurface warm layer regions influenced by the Kuroshio Branch Current West of Kyushu (KBCWK) and the Tsushima Current (TSC) and the shallow subsurface warm layer regions influenced by the Yellow Sea Bottom Cold Water (YSBCW). Jeju Island is a border dividing the two regions.Statistical analysis shows that 70–90% of the 10 strongest typhoons on the KP passed through the eastern side of Jeju Island where the warm ocean currents exist at the subsurface. In contrast, the majority of typhoons which passed over the YSBCW regions where cold water exists at the subsurface, along the western side of Jeju Island, experience a large surface temperature cooling due to the storm’s self-induced vertical mixing and upwelling, resulting in a significant decrease in intensity. These results demonstrate that the intensity of the KP-landfall typhoons is very sensitive to the storm’s track and how the difference in the upper ocean thermal structures in small areas can affect the typhoon intensity change.