Observation of near-inertial waves in the wake of four typhoons in the northern South China Sea

Qinglong Gong; Qixiang Wang; Liang Chen; Yina Diao; Xuejun Xiong; Jilin Sun; Xianqing Lv

doi:10.1038/s41598-023-29377-3

Observation of near-inertial waves in the wake of four typhoons in the northern South China Sea

Sci Rep. 2023 Feb 23;13(1):3147. doi: 10.1038/s41598-023-29377-3.

Authors

Qinglong Gong^{1

2

3}, Qixiang Wang^{1

3}, Liang Chen^{2

4

5}, Yina Diao^{1

3}, Xuejun Xiong^{6

7

8}, Jilin Sun^{1

3}, Xianqing Lv^{9

10}

Affiliations

¹ Frontier Science Center for Deep Ocean Multispheres and Earth System (FDOMES) and Physical Oceanography Laboratory, Ocean University of China, Qingdao, 266100, China.
² First Institute of Oceanography, Ministry of Natural Resources, Qingdao, 266061, China.
³ Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266200, China.
⁴ Founctional Laboratory for Regional Oceanography and Numerical Modeling, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao, 266237, China.
⁵ Laboratory for Regional Oceanography and Numerical Modeling, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao, 266237, China.
⁶ First Institute of Oceanography, Ministry of Natural Resources, Qingdao, 266061, China. xiongxj@fio.org.cn.
⁷ Founctional Laboratory for Regional Oceanography and Numerical Modeling, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao, 266237, China. xiongxj@fio.org.cn.
⁸ Laboratory for Regional Oceanography and Numerical Modeling, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao, 266237, China. xiongxj@fio.org.cn.
⁹ Frontier Science Center for Deep Ocean Multispheres and Earth System (FDOMES) and Physical Oceanography Laboratory, Ocean University of China, Qingdao, 266100, China. xqinglv@ouc.edu.cn.
¹⁰ Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266200, China. xqinglv@ouc.edu.cn.

Abstract

Based on the velocity and temperature data recorded by two acoustic Doppler current profilers (ADCPs) at a mooring system deployed in the northern South China Sea (SCS), this study investigates the characteristics of near-inertial waves (NIWs) induced by typhoons Bebinca, Barijat, Mangkhut and Yutu in 2018. For the dynamical response, besides the motion of near inertial frequency induced by typhoons, the motion of 2 f ([1.80-2.20] f, f is the local inertial frequency) and f D₁ (a harmonic wave with a frequency equal to the sum of frequencies of NIWs and diurnal tides) frequency will also increase. For near-inertial motions, the maximum near-inertial kinetic energy (NIKE) is confined to depths above 150 m. For stronger (weaker) wind forcing, the longer (shorter) the response time of the ocean to the atmospheric forcing is, and the shorter (longer) the response time is required in relaxation stage. There are upward and downward propagating energies after the passage of typhoons, and the upward propagating energy mainly occur in the stage of the geostrophic balance adjustment. The current structure suggests that the NIWs in the vertical direction are two antisymmetric rotary vortices in a near-inertial period, which is similar to the structure of the Langmuir circulation. Besides, the horizontal near-inertial currents (NICs) are much stronger than the vertical NICs, and the stronger the NIWs are, the stronger the horizontal NICs relative to the vertical NICs are. For the temperature response, the temperature variation reflects a clear stratified vertical structure. In the forcing stage, the upper layer becomes colder, the lower layer becomes warmer, and the thickness and intensity of the thermocline decrease. In the relaxation stage, the upper layer warms and the lower layer cools, and the thickness and intensity of thermocline increase.