Dramatic temperature variations in the Yellow Sea during the passage of typhoon Lekima (2019)

During the passage of Typhoon Lekima over the stratified Yellow Sea (YS) in August 2019, dramatic bottom temperature cooling of 2–5 °C was observed in northern coastal oceans of the Shandong Peninsula. In the current study, satellite observations and high-resolution numerical simulations were combined to investigate three-dimensional temperature changes in the YS during Lekima's passage and the underlying dynamics. Results indicated that the YS showed spatially coherent surface cooling and subsurface warming, primarily due to enhanced vertical mixing. The strongest surface temperature cooling of 4–8 °C occurred just over the southern bottom slope in the North YS, for which tidal mixing and bottom slope were also important factors through maintaining strong thermal stratification and inducing locally enhanced upwelling. In contrast, bottom temperature changes were most significant in coastal oceans in the western YS, showing dramatic cooling in northern coastal oceans of the Shandong Peninsula but warming as high as 8 °C in southern coastal oceans of the Shandong and Liaodong Peninsulas. Surface winds drove northward/shoreward Ekman transports in the North/South YS. This resulted in surface water convergence and downwelling in southern coastal oceans of the Shandong and Liaodong Peninsulas but divergence and upwelling in northern coastal oceans of the Shandong Peninsula. Downwelling generated bottom warming through transporting downward surface warm water. In the bottom layer, southward pressure gradient force drove shoreward advection of cold water to induce temperature cooling in nearshore regions. The current study provides significantly more insights into oceanic responses to passages of typhoons in the YS, especially in coastal oceans, which are one of the most intensively maricultured areas in the world.