[A-AS04] Advances in Tropical Cyclone Research: Past, Present, and Future

[AAS04-P02] Ocean thermal responses to the intensification of typhoons in the shallow East China Sea

*Thi-Kieu-Diem Nguyen¹, Po-Chun Hsu^1,2 (1.Center for Space and Remote Sensing Research, National Central University, 2.Institute of Hydrological and Oceanic Sciences, National Central University)

Keywords:Typhoon intensification, Shallow water, East China Sea, Ocean thermal responses

Typhoons are considered one of the most destructive natural disasters on earth, threatening the safety of human life and property, especially in coastal areas. Accurate typhoon forecasts are crucial to reducing the impact of typhoons. In this study, seven typhoon cases of ocean thermal responses consist of Typhoon Olga (1999), Kompasu (2010), Damrey (2012), Malakas (2016), Nanmadol (2017), Kong-Rey (2018), and Bavi (2020) over shallow water areas were analyzed to understand the process of typhoon intensification. Based on satellite, reanalysis, in situ observations of ocean thermal structure, and ocean mixing models, this study examined the ocean-typhoon interaction around the shallow East China Sea region under the intensification of typhoons. Since 1980, there are four typhoons intensified to category 1 (Olga (1999), Damrey (2012), Nanmadol (2017), and Kong-Rey (2018)) as they entered the shallow ECS. Typhoon Kompasu (2010) and Bavi (2020) are the two strongest (category 3) typhoons with similar paths that moved into the Yellow Sea. Typhoon Malakas (2016) also reached category 3, however, its path to Japan. The sea surface temperature cooling was induced most of 3℃ by Kompasu (2010), with the strongest effects on the right of the typhoon tracks. Typhoon Bavi caused a large sea surface temperature cooling effect (~8℃), which was attributed to the abnormal ocean thermal structure, which included over 30℃ warming sea surface temperature and the predominance of the Yellow Sea cold bottom water, as well as strong stratification effects, which may have prevented vertical mixing. Based on the ocean mixing model, the shallow water depth could inhibit the sea surface temperature cooling during the intensification of both typhoons. Because, in shallow water, the warm sea surface temperature is maintained due to a lack of deep cold water. Moreover, the air-sea heat flux was generally 700 W/m² during Typhoon Bavi’s intensification phase, which supplied the intense energy from the ocean to the typhoon. Likewise, the atmospheric environment also supported favorable conditions for the intensification process of Typhoon Bavi. Near-saturated relative humidity (over 80%) at lower and mid-levels contributed to the typhoon’s intensity evolution, notably as it reached category 3. The ocean thermal responses to the intensification of typhoons were completely quantified. The results could explain the intensification of seven typhoons compared with other typhoons that did not intensify over this incredible region and the effect of shallow water on changes in the typhoon intensity, as well as support the forecast of ocean behavior toward future tremendous events.