Based on the Moderate-Resolution Imaging Spectroradiometer (MODIS) sea surface temperature (SST) of ten years (2000-2009) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color data of 13 years (1998-2010), the Kuroshio oceanic front exists between two entirely different water masses in the East China Sea, namely, the Kuroshio and continental shelf waters. The Kuroshio thermal front (derived from the SST data) disappears in summer due to the spatially uniform surface heating, whereas the Kuroshio ocean color front in summer is distinct and exhibits the same spatial pattern along the shelf break of the deep Okinawa Trough as in winter. The Kuroshio thermal front has one bifurcation at about (126° E, 28° N) and extends northward toward the Cheju Island lasting from December to March, but this kind of branch is absent in the ocean color data.

This study presents a risk prediction of coastal hazards induced by typhoons, which are a severe natural hazard that often occur in coastal regions. Taking the coastal hazards happened in Shenzhen as a case study, where is a southeast coastal city of China, we described a methodology to predict the typhoon wind-surge-wave hazard. A typhoon empirical tracking model was adopted to construct full-track typhoon events for 1000 years, based on the statistical characteristics of observed typhoons from satellite imageries. For each individual typhoon, a wind-field model is applied to compute the wind speeds, while the Simulating Waves Nearshore and Advanced Circulation (SWAN+ADCIRC) coupled model is applied to simulate the significant wave heights (SWHs) and storm surge heights. By frequency distribution histogram, it is noted that there exhibits a heavy tail in the probability distribution of maximum surge heights and a thin tail of the peak wind speeds and SWHs in the coastal area of Shenzhen, China. Using the Generalized Pareto Distribution (GPD) model, the extreme values of typhoon wind-surge-wave associated with various return periods can be predicted. Taking account into the combined effects of the wind, surge and wave, the joint hazard maps of typhoon wind-surge-wave can be produced for the study area. The methodology of this case study can provide a new reference for risk prediction of coastal hazards induced by typhoon in similar coastal regions like Shenzhen, China.

Based on satellite and analysis data and in situ observations acquired during May 23, 2017 to May 19, 2018, the spatiotemporal variations of the along-slope counter-flow off northeastern Taiwan were investigated. It was observed that the along-slope counter-flow in the subsurface layer was uplifted and lowered significantly during the study period. The counter-flow was significantly uplifted (lowered) while the sea surface was during an interval of positive (negative) geostrophic velocity anomaly (GVA) curl. The vertical migration of the counter-flow was also found closely linked with the Kuroshio intrusion (KI) to the northeast of Taiwan. The depths of both the upper boundary and the axis of the counter-flow were found proportional to the KI variance along the western continental slope off northeastern Taiwan. More importantly, it was established that the variation of the KI to the northeast of Taiwan had better correlation with the counter-flow than the Kuroshio derived from altimetry data. Thus, further study of the variation and mechanism of the along-slope counter-flow is needed to improve the understanding and prediction of the KI in the area of northeastern Taiwan, as well as the biochemical systems and marine economy in the East China Sea in the future.

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.