Abstract This is a study of the storm surge trends in some of the typhoon-prone coastal areas of China. An unstructured-grid, storm surge-wave-tide coupled model was established for the coastal areas of Zhejiang, Fujian and Guangdong provinces. The coupled model has a high resolution in coastal areas, and the simulated results compared well with the in situ observations and satellite altimeter data. The typhoon-induced storm surges along the coast of the study areas were simulated based on the established coupled model for the past 20 years (1997–2016). The simulated results were used to analyze the trends of the storm surges in the study area. The extreme storm surge trends along the central coast of Fujian Province reached up to 0.06 m/y, significant at the 90% confidence level. The duration of the storm surges greater than 1.0 and 0.7 m had an increasing trend along the coastal area of northern Fujian Province, significant at confidence levels of 70%–91%. The simulated trends of the extreme storm surges were also validated by observations from two tide gauge stations. Further studies show that the correlation coefficient (RTE) between the duration of the storm surge greater than 1 m and the annual ENSO index can reach as high as 0.62, significant at the 99% confidence level. This occurred in a location where the storm surge trend was not significant. For the areas with significant increasing storm surge trends, RTE was small and not significant. This study identified the storm surge trends for the full complex coastline of the study area. These results are useful both for coastal management by the government and for coastal engineering design.

Study of Storm Surge Trends in Typhoon-prone Coastal Areas Based on Observations And Surge-wave Coupled Simulations

Spatiotemporal variations and extreme value analysis of significant wave height in the South China Sea based on 71-year long ERA5 wave reanalysis

Previously,most ocean circulation models have overlooked the role of the surface waves.As a result,these models have produced insufficient vertical mixing,with an under-prediction of the mixing layer(ML)depth and an over-prediction of the sea surface temperature(SST),particularly during the summer season.As the ocean surface layer determines the lower boundary conditions of the atmosphere,this deficiency has severely limited the performance of the coupled ocean-atmospheric models and hence the climate studies.To overcome this shortcoming,a new parameterization for the wave effects in the ML model that will correct this systematic error of insufficient mixing.The new scheme has enabled the mixing layer to deepen,the surface excessive heating to be corrected,and an excellent agreement with observed global climatologic data.The study indicates that the surface waves are essential for ML formation,and that they are the primer drivers of the upper ocean dynamics;therefore,they are critical for climate studies.

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The role of surface waves in the ocean mixed layer

A one-way coupled POMgcs-SWAN model is applied to study the impacts of three wave processes, i.e. Langmuir turbulence, Coriolis-Stokes forcing (CSF) and resolved-scale Craik-Leibovich vortex forcing (CLVF), on ocean dynamics in Bohai Sea in summer. Both CSF and CLVF are included in the horizontal momentum equation. The level-2.5 Mellor-Yamada turbulence closure scheme is modified to contain the parameterization of Langmuir turbulence. Numerical results show that this improved model reproduces the sea surface temperature (SST) better than the original one. All of these wave effects considerably contribute to temperature variability at different vertical levels, with the maximum temperature change of about 0.4 °C. Based on the diagnostic experiments, the impacts of the CSF and CLVF are much weaker than that of Langmuir turbulence. Those wave processes reduce the current velocity and make the current more vertically uniform. The horizontal distribution of Langmuir number indicates that the Langmuir turbulence is prevalent in Bohai Sea. The large vertical kinematic viscosity coefficients, containing the Langmuir turbulence, would lead to a strong vertical mixing.

Impacts of surface gravity waves on summer ocean dynamics in Bohai Sea

This study investigated the performance of two ocean wave models, that is, Simulation Wave Nearshore (SWAN) and WAVEWATCH-III (WW3), and the interannual and seasonal variability of transport induced by Stokes drift during the period from 1989 to 2019. Three types of sea surface wind products were used for wave simulation: the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim, the Cross Calibrated Multi-Platform Version 2.0 (CCMP V2.0) from Remote Sensing Systems (RSS), and the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS). The modeling was validated against wave measurements from the Jason-2 altimeter in 2015. The analysis found that the root mean square error (RMSE) of significant wave height (SWH) from the WW3 model using CCMP wind data was 0.17 m, which is less than the ~0.6-m RMSE of SWH from the SWAN model using the other types of wind data. The simulations from the WW3 model using CCMP wind data indicated that the Stokes transport is up to 2 m2/s higher in the South China Sea and Japan Sea than that at other ocean regions in January. The interannual variation showed that the Stokes transport generally increased from 0.25 m2/s in 1989 to 0.35 m2/s in 2018. We also found that the accuracy of the sea surface temperature (SST) simulation using the Stony Brook Parallel Ocean Model (sbPOM) is improved by as much as 0.5 °C when Stokes transport is considered to validate the sbPOM-simulated SST against the measurements from Argo in 2012–2015. In particular, the Stokes transport has a negative effect on Summer (March to June) and has a positive effect in Autumn (July to September), which is probably caused by the tropical cyclones.

Analysis of Wave-Induced Stokes Transport Effects on Sea Surface Temperature Simulations in the Western Pacific Ocean

Extreme wave climate variability in South China Sea

The wave-forcing ‘Coriolis-Stokes forcing’ and ‘Stokes-vortex force’ induced by Stokes drift affect the upper ocean jointly. To study the effect of the wave-induced Stokes drift on the dynamics of the ocean mixed layer, a new three-dimensional (3D) numerical model is derived using the primitive basic equations and Eulerian wave averaging. The Princeton Ocean Model (POM), a 3D primitive equation ocean model is used with the upper wave-averaged basic equations. The global ocean circulation is simulated using the POM model, and the Stokes drift is evaluated based on the wave data generated by WAVEWATCH III. We compared simulations with and without the Stokes drift. The results show that the magnitude of the Stokes drift is comparable with the Eulerian mean current. Including the Stokes drift in the ocean model affects both the Eulerian current and the Lagranian drift and causes the vertical mixing coefficients to increase.

Sheng Dong

Papers

Extreme wave climate variability in South China Sea

Effect of wave-induced Stokes drift on the dynamics of ocean mixed layer