[A-CG47] Dynamics of Oceanic and Atmospheric Waves, Vortices, and Circulations

[ACG47-02] Contribution of high-mode near-inertial waves to enhanced typhoon-induced sea surface temperature cooling in the South China Sea

Shukui Cheng¹, *Anzhou Cao¹, Jinbao Song¹, Xinyu Guo² (1.Zhejiang Univ., 2.CMES)

Keywords:Near-inertial waves, Typhoon, Sea surface temperature cooling, High-mode

Sea surface temperature cooling (SSTC) is an important indicator of the ocean response to typhoons and is a factor in the evolution of typhoons. Understanding the intricate mechanisms underlying typhoon-induced SSTC is important. Previous studies indicate that 12 factors related to typhoon characteristics and pre-typhoon ocean conditions can influence typhoon-induced SSTC. In addition to these factors, we report here that the modal content of typhoon-induced near-inertial waves (NIWs) is also crucial in typhoon-induced SSTC. Based on the numerical simulation, we investigated the SSTC induced by typhoons Megi (2010), Linfa (2015) and Sarika (2011), which had relatively similar tracks in the South China Sea. As the strongest (weakest) typhoon, Megi (Sarika) induced the largest (smallest) SSTC, which is consistent with the traditional understanding that stronger typhoons usually induce larger SSTC than weaker typhoons. However, the SSTC induced by the moderate typhoon Linfa was nearly comparable to that induced by Megi, while Linfa had a wind power input an order of magnitude smaller. A comparison of NIWs induced by Linfa and Megi showed that the former contained a larger proportion of high modes, substantially contributing to vertical shear. Consequently, the vertical mixing coefficient during Linfa reached one third of that during Megi. Because the SSTC is primarily influenced by vertical mixing, which is dominated by vertical diffusion at the mixed layer depth, the relatively strong vertical mixing coefficient and large temperature gradient during Linfa ultimately resulted in the SSTC nearly comparable to that induced by Megi.