Observation of Near-Inertial Waves Induced by Typhoon Mitag (2019) on the Southwestern East China Sea Continental Slope

Abstract

Based on horizontal velocity data recorded by a moored acoustic Doppler current profiler (ADCP) deployed on the southwestern continental slope of the East China Sea (ECS), this study investigates the characteristics of near-inertial waves (NIWs) induced by typhoon Mitag in October 2019. The results indicated that Mitag-induced near-inertial kinetic energy (NIKE) was mainly concentrated above 290 m and was subsurface-intensified; both the maximum velocity and kinetic energy of the NIWs occurred at a depth of 100 m and were 0.21 m/s and 23.01 J/m3, respectively. The rotary vertical wavenumber spectra suggested that both downward and upward energy propagation existed. However, upward energy propagation was much smaller than downward energy propagation, mainly in the 0.007–0.014 cpm wavenumber band. The NIWs had an e-folding timescale of 9.5 days and were red-shifted as a result of the Doppler shift of the Kuroshio. Normal mode analysis suggested that the NIWs were dominated by the first and fourth baroclinic modes, which together accounted for 76.7% of the total NIKE. Spectral analysis showed that although the spectral density of the semidiurnal internal tide (M2) peak overwhelmed that of the NIWs by a factor of approximately 30, the shear strength generated by the NIWs was comparable to that of the semidiurnal internal tide (M2), which plays an important role in upper ocean mixing on the southwestern continental slope of the ECS. In addition, the bicoherence analysis suggested that a harmonic wave (M2–f) was generated via the nonlinear interaction between the NIWs and semidiurnal internal tide (M2), which reflects the energy dissipation mechanism of semidiurnal tides and NIWs on the southwestern continental slope of the ECS.

Vertical Structure and Seasonal Variability of Shear on the Southwestern Continental Slope of the East China Sea

“…Moreover, prominent spectral densities appear around the frequencies of 0 and M 2 throughout the observation depth layer. For the local internal wave field, the D2 ITs overwhelm other internal wave signals, which is consistent with previous studies [23,29,32,36]. The spectral densities of D1 ITs are only less than those of the D2 ITs.…”

“…At the mooring, nonlinear interactions between internal waves occurred because of spectral peaks that appeared at the MO 3 , MK 3 , M 4 , and MS 4 frequencies. Although the near-inertial frequency shows the characteristic of broadband, when significant near-inertial waves occur at the mooring, such as that induced by the passage of a typhoon, a spectral peak will appear near the local inertial frequency (f ) [23].…”

“…Park et al [22] found wind-induced NIWs with downward-propagating energy on the ECS shelf break. Ouyang et al [23] observed typhoon-induced NIWs on the southwestern continental slope of the ECS, which had an e-folding timescale of 9.5 days and were red-shifted as a result of the Doppler shift of the Kuroshio. In addition, Yang et al [24] indicated that the generation mechanisms of the NIWs on the continental slope vary, including typhoon, wind burst, and lateral propagation, based on almost one year of in situ observations.…”

Three Types of Typhoon‐Induced Upwellings Enhance Coastal Algal Blooms: A Case Study

“…29°N is the critical latitude for the PSI of the semidiurnal internal tides (Ansong et al., 2018; MacKinnon et al., 2013), which is consistent with the location of our study region and the predominant M 2 semidiurnal tide here. Besides, the occurrence of PSI has been observed in the ECS (Yang et al., 2020) and has been examined under typhoon conditions (Ouyang et al., 2022). We concluded that the PSI, as well as strengthened near‐inertial mixing and tidal mixing during Chan‐hom, contributed to the algal bloom by mixing KSSW into the upper layer.…”

Measure of Utilizing Space Database Information for Improvement of Efficient Disaster Management (Focusing on Nuclear Power Plant Accidents)

“…The damage caused by disasters is increasing worldwide, with hundreds of thousands of deaths due to the occurrence of complex large-scale disasters such as the 2011 Fukushima nuclear disaster [1,2], the 2010 Haiti earthquake [3,4], and the 2004 Indian tsunami [5]. South Korea has also experienced human casualties and property damage caused by large-scale disasters in the past 10 years, such as typhoon Mitag [6] in 2009, the hydrofluoric acid spill accident in Gumi [7] in 2013, and the collapse of the Mauna Ocean Resort gymnasium [8] and sinking of the motor vessel Sewol [9] in 2014. Such damage is aggravated due to poor disaster response.…”