Typhoon-Induced Ocean Waves and Stokes Drift:A Case Study of Typhoon Mangkhut(2018)

Ocean waves and Stokes drift are generated by typhoons.This study investigated the characteristics of ocean waves and wave-induced Stokes drift and their effects during Typhoon Mangkhut using European Centre for MediumRange Weather Forecasts(ECMWF)ERA5 datasets and observational data.The results revealed that the typhoon generated intense cyclones and huge typhoon waves with a maximum wind speed of 45 m/s,a minimum pressure of955 h Pa,and a maximum significant wave height of 12 m.The Stokes drift caused by typhoon waves exceeded 0.6m/s,the Stokes depth scale exceeded 18 m,and the maximum Stokes transport reached 6 m^(2)/s.The spatial distribution of 10-m wind speed,typhoon wave height,Stokes drift,Stokes depth,and Stokes transport during the typhoon was highly correlated with the typhoon track.The distribution along the typhoon track showed significant zonal asymmetry,with greater intensity on the right side of the typhoon track than on the left side.These findings provide important insights into the impact of typhoons on ocean waves and Stokes drift,thus improving our understanding of the interactions between typhoons and the ocean environment.This study also investigated the contribution of Stokes transport to the total net transport during typhoons using Ekman-Stokes Numbers as a comparative measure.The results indicated that the ratio of Stokes transport to the total net transport reached up to 50%within the typhoon radius,while it was approximately 30%outside the radius.Strong Stokes transport induced by typhoon waves led to divergence in the transport direction,which resulted in upwelling of the lower ocean as a compensation current.Thus,Stokes transport played a crucial role in the vertical mixing of the ocean during typhoons.The findings suggested that Stokes transport should be paid more attention to,particularly in high latitude ocean regions,where strong winds can amplify its effects.

Analysis of Sea Surface Temperature Cooling in Typhoon Events Passing the Kuroshio Current

The aim of this study is to investigate the sea surface temperature(SST) cooling as typhoons pass the Kuroshio Current.A numerical circulation model,denoted as the Stony Brook Parallel Ocean Model(sbPOM),was used to simulate the SST,which includes four wave-induced effect terms(i.e.,radiation stress,nonbreaking waves,Stokes drift,and breaking waves) simulated using the third-generation wave model,called WAVEWATCH-Ⅲ(WW3).The significant wave height(SWH) measurements from the Jason-2 altimeter were used to validate the WW3-simulated results,yielding a root mean square error(RMSE) of less than 0.50 m and a correlation coefficient(COR) of approximately 0.93.The water temperature measured from the Advanced Research and Global Observation Satellite was applied to validate the model simulation.Accordingly,the RMSE of the SST is 0.92℃ with a COR of approximately 0.99.As revealed in the sbPOM-simulated SST fields,a reduction in the SST at the Kuroshio Current region was observed as a typhoon passed,although the water temperature of the Kuroshio Current is relatively high.The variation of the SST is consistent with that of the current,whereas the maximum SST lagged behind the occurrence of the peak SWH.Moreover,the Stokes drift plays an important role in the SST cooling after analyzing four wave-induced terms in the background of the Kuroshio Current.The sensitivity experiment also showed that the accuracy of the water temperature was significantly reduced when including breaking waves,which play a negative role in the inside part of the ocean.The variation in the mean mixing layer depth(MLD) showed that a typhoon could enhance the mean MLD in the Kuroshio Current area in September and October,whereas a typhoon has little influence on the mean MLD in the Kuroshio Current area in May.Moreover,the mean MLD rapidly decreased with the weakening of the strong wind force and wave-induced effects when a typhoon crossed the Kuroshio Current.

Effect of oceanic current on typhoon-wave modeling in the East China Sea

We use the WAVEWATCH-III model to quantify the effect of oceanic current on typhoon-wave modeling in the East-China-Sea（ECS）.Typhoons Jelawat and Saomai in the autumn of 2000 are hindcasted.The oceanic currents in the ECS are mainly constituted of Kuroshio and typhoon-generated currents.The results show distinguishable differences in wave height and wave period under the typhoon conditions.The oceanic current causes the maximum differences,of up to a 0.5 m significant wave height and a 1 s mean wave period.Comparisons between typhoons Jelawat and Saomai show the dependence of the current effect on the typhoon characteristics.

Estimation and Prediction of Typhoons and Wave Overtopping in Qingdao, China

This study aims to estimate and predict the impact of climate change on typhoons and wave overtopping during typhoon progresses in Qingdao, China. The SWAN wave model is used to simulate wave elements. The scale coefficients of wave overtopping are estimated using an empirical prediction formula. A total of 75 tropical cyclones affected Qingdao from 1949 to 2019. These tropical cyclones can be grouped into eight categories according to typhoon tracks. Typhoon wind speed during Track G is projected to decrease, and those of the other seven typhoon progresses will increase by 0.35% – 0.75% in 2025, 0.69% – 1.5% in 2035, and 1.38% – 3.0% in 2055. The significant wave height and wave overtopping outside the bay are greater than those inside the bay. Among the 506 typical points selected, the maximum values of the significant wave height and wave overtopping inside the bay are mainly distributed in the range of 0 – 2 m and 0 – 60 m^3 km^(-1) s^(-1), respectively. The increments of the significant wave height and wave overtopping of Track F are most obvious. The significant wave height of Track F will increase by 50.5% in 2025, 51.8% in 2035, and 53.4% in 2055. In the 2℃ scenario, the maximum value of wave overtopping of Track F will increase by 21.9% in 2025, 24.3% in 2035, and 29.5% in 2055. In the 4℃ scenario, the maximum value of wave overtopping of Track F will increase by 21.9% in 2025, 24.3% in 2035, and 29.5% in 2055.

Numerical simulation and preliminary analysis of typhoon waves during three typhoons in the Yellow Sea and East China Sea

In this study,typhoon waves generated during three typhoons(Damrey(1210),Fung-wong(1416),and Chan-hom(1509))in the Yellow Sea and East China Sea were simulated in a simulating waves nearshore(SWAN)model,and the wind forcing was constructed by combining reanalyzed wind data with a Holland typhoon wind model.Various parameters,such as the Holland fitting parameter(B)and the maximum wind radius?,were investigated in sensitivity experiments in the Holland model that affect the wind field construction.Six different formulations were considered and the parameters determined by comparing the simulated wind results with in-situ wind measurements.The key factors affecting wave growth and dissipation processes from deep to shallow waters were studied,including wind input,whitecapping,and bottom friction.Comparison with in-situ wave measurements suggested that the KOMEN scheme(wind input exponential growth and whitecapping energy dissipation)and the JONSWAP scheme(dissipation of bottom friction)resulted in good reproduction of the significant wave height of typhoon waves.A preliminary analysis of the wave characteristics in terms of wind-sea and swell wave revealed that swell waves dominated with the distance of R to the eye of the typhoon,while wind-sea prevailed in the outer region up to six to eight times the R values despite a clear misalignment between wind and waves.The results support the hypothesis that nonlinear wave-wave interactions may play a key role in the formation of wave characteristics.

Numerical investigation of ocean waves generated by three typhoons in offshore China

The influences of the three types of reanalysis wind fields on the simulation of three typhoon waves occurred in2015 in offshore China were numerically investigated.The typhoon wave model was based on the simulating waves nearshore model(SWAN),in which the wind fields for driving waves were derived from the European Centre for Medium-Range Weather Forecasts(ECMWF)Re-Analysis-Interim(ERA-interim),the National Centers for Environmental Prediction climate forecast system version 2(CFSv2)and cross-calibrated multi-platform(CCMP)datasets.Firstly,the typhoon waves generated during the occurrence of typhoons Chan-hom(1509),Linfa(1510)and Nangka(1511)in 2015 were simulated by using the wave model driven by ERA-interim,CFSv2 and CCMP datasets.The numerical results were validated using buoy data and satellite observation data,and the simulation results under the three types of wind fields were in good agreement with the observed data.The numerical results showed that the CCMP wind data was the best in simulating waves overall,and the wind speeds pertaining to ERA-Interim and CCMP were notably smaller than those observed near the typhoon centre.To correct the accuracy of the wind fields,the Holland theoretical wind model was used to revise and optimize the wind speed pertaining to the CCMP near the typhoon centre.The results indicated that the CCMP wind-driven SWAN model could appropriately simulate the typhoon waves generated by three typhoons in offshore China,and the use of the CCMP/Holland blended wind field could effectively improve the accuracy of typhoon wave simulations.

Analysis of the typhoon wave distribution simulated in WAVEWATCH-Ⅲ model in the context of Kuroshio and wind-induced current

To investigate the relationship between surface currents and wave distributions in typhoons,we took the Typhoon Talim in 2017 as a case,and found that the track of the typhoon winds up to 50 m/s was almost consistent with the Kuroshio track,particularly from September 13 to 16,2017.The surface current data,derived from the NCEP Climate Forecast System Version 2(CFSv2)from the National Center of Atmospheric Research(NCAR),revealed that the speed of the wind-induced current exceeded that of the Kuroshio in the region with the maximum wind speed.In this study,was utilized a third-generation numeric wave model,WAVEWATCH-Ⅲ(the latest version 5.16),developed by the National Oceanic and Atmospheric Administration(NOAA),to simulate the wave fields of Typhoon Talim using the European Centre for Medium-Range Weather Forecasts(ECMWF)reanalysis wind data in 0.125°×0.125°grid as the forcing field.We found that the root-mean-square error(RMSE)of the significant wave height(SWH)was 0.34 m when validated against measurements from altimeter Jason-2.In addition,we discovered that the SWH had a similar tendency to the change in the surface current speed that was approximately 0.5 m/s at the beginning of Typhoon Talim.However,the relationship became weak as the surface current speed was below 0.2 m/s.Our findings show that the distribution of typhoon waves is resulted from the interaction of surface current and the wind-sea portion of the wave system,since the distribution pattern of wind-sea is consistent with the surface current,and there is a weak relationship between surface current and swell.

Evaluation of Typhoon Waves Simulated by Wave Watch-Ⅲ Model in Shallow Waters Around Zhoushan Islands

In this study, we simulated typhoon waves in the shallow waters around the Zhoushan Islands using the WaveWatch-Ⅲ(WW3) model version 5.16, the latest version released by the National Oceanic and Atmospheric Administration. Specifically, we used in-situ measurements to evaluate the performance of seven packages of input/dissipation source terms in the WW3 model. We forced the WW3 model by wind fields derived from a combination of the parametric Holland model and high-resolution European Center for Medium-Range Weather Forecasts(ECMWF) wind data in a 0.125? grid, herein called H-E winds. We trained the H-E winds by fitting a shape parameter B to buoy-measured observations, which resulted in a smallest root mean square error(RMSE) of 3 m s^(-1) for B, when treated as a constant 0.4. Then, we applied the seven input/dissipation terms of WW3, labelled ST1, ST2, ST2+STAB2, ST3, ST3+STAB3, ST4, and ST6, to simulate the significant wave height(SWH) up to 5 m during typhoons Fungwong and Chan-hom around the Zhoushan Islands. We then compared the SWHs of the simulated waves with those measured by the in-situ buoys. The results indicate that the simulation using ST2 performs best with an RMSE of 0.79 m for typhoon Fung-wong and an RMSE of 1.12 m for typhoon Chan-hom. Interestingly, we found the simulated SWH results to be relatively higher than those of the observations in the area between Hangzhou Bay and the Zhoushan Islands. This behavior is worthy of further investigation in the future.

Evaluation of numerical wave model for typhoon wave simulation in South China Sea

The simulating waves nearshore(SWAN) model has typically been designed for wave simulations in near-shore regions. In this study, the model's applicability to the simulation of typhoon waves in the South China Sea(SCS) was evaluated. A blended wind field, consisting of an interior domain based on Fujita's model and an exterior domain based on Takahashi's model, was used as the driving wind field. The waves driven by Typhoon Kai-tak over the SCS that occurred in 2012 were selected for the numerical simulation research. Sensitivity analyses of time step, grid resolution, and angle resolution were performed in order to obtain optimal model settings. Through sensitivity analyses, it can be found that the time step has a large influence on the results, while grid resolution and angle resolution have a little effect on the results.

Development of typhoon driven wave nowcasting model in Southeast China Sea

Using optimal interpolation data assimilation of observed wave spectrum around Northeast coast of Taiwan Island, the typhoon driven wave nowcasting model in Southeast China Sea is setup. The SWAN (simulating waves nearshore) model is used to calculate wave field and the input wind field is the QSCAT/NCEP (Quick Scatterometer/National Centers for Environmental Prediction) data. The two-dimensional wavelet transform is applied to analyze the X-band radar image of nearshore wave field and it reveals that the observed wave spectrum has shoaling characteristics in frequency domain. The reverse calculation approach of wave spectrum in deep water is proposed and validated with experimental tests. The two-dimensional digital low-pass filter is used to obtain the initialization wave field. Wave data during Typhoon Sinlaku is used to calibrate the data assimilation parameters and test the reverse calculation approach. Data assimilation corrects the significant wave height and the low frequency spectra energy evidently at Beishuang Station along Fujian Province coast, where the entire assimilation indexes are positive in verification moments. The nowcasting wave field shows that the present model can obtain more accurate wave predictions for coastal and ocean engineering in Southeast China Sea.

Optimization of multi-model ensemble forecasting of typhoon waves

Accurately forecasting ocean waves during typhoon events is extremely important in aiding the mitigation and minimization of their potential damage to the coastal infrastructure, and the protection of coastal communities. However, due to the complex hydrological and meteorological interaction and uncertainties arising from different modeling systems, quantifying the uncertainties and improving the forecasting accuracy of modeled typhoon-induced waves remain challenging. This paper presents a practical approach to optimizing model-ensemble wave heights in an attempt to improve the accuracy of real-time typhoon wave forecasting. A locally weighted learning algorithm is used to obtain the weights for the wave heights computed by the WAVEWATCH III wave model driven by winds from four different weather models （model-ensembles）. The optimized weights are subsequently used to calculate the resulting wave heights from the model-ensembles. The results show that the opti- mization is capable of capturing the different behavioral effects of the different weather models on wave generation. Comparison with the measurements at the selected wave buoy locations shows that the optimized weights, obtained through a training process, can significantly improve the accuracy of the forecasted wave heights over the standard mean values, particularly for typhoon-induced peak waves. The results also indicate that the algorithm is easy to imnlement and practieal for real-time wave forecasting.

Wave-tide-surge coupled model simulation for Typhoon Maemi

Reasonably accurate predictions of wave heights, current and elevations during storm events are vital information for marine operations and design of offshore and coastal structures in the surrounding seas of Korea Peninsula. Ocean circulation and wind-wave models have traditionally been run separately, but recent researches have identified potentially important interactions between current and wave motions. The coupled tide-surge and the WAM wave models at the atmospheric boundary layer and bottom boundary layer around the Korea Peninsula are applied for the Typhoon Maemi （0314） event. Communication between the models is aehievod using MPI. Results are compared with coastal tide gauges and moored wave buoys and comparisons are also made between wave computations from the coupled model and the independent third generation wave models. Results suggest that applying the fide-surge-coupled model can be an effective means of obtaining wave and storm surge predictions simultaneously.

A statistical analysis of typhoon frequency and application in design wave height

A typhoon leading is an important natural disaster to many disasters to China. A giant wave caused by it has brought large threat for an offshore project. Based on the maximum entropy principle,one new model which has 4 undetermined parameters is constructed,which is called the discrete maximum entropy probabilistic model. In practical applications,the design wave height is considered as soon as possible in a typhoon affected sea areas,the result fits the observed data well. Further more this model does not have the priority compared with other distributions as Poisson distribution. The model provides a theoretical basis for the engineering design more reasonable when considering typhoon factors comprehensively.

Simulation of the extreme waves generated by typhoon Bolaven (1215) in the East China Sea and Yellow Sea

Record-breaking high waves occurred during the passage of the typhoon Bolaven（1215）（TYB） in the East China Sea（ECS） and Yellow Sea（YS） although its intensity did not reach the level of a super typhoon.Winds and directional wave measurements were made using a range of in-situ instruments mounted on an ocean tower and buoys.In order to understand how such high waves with long duration occurred,analyses have been made through measurement and numerical simulations.TYB winds were generated using the TC96 typhoon wind model with the best track data calibrated with the measurements.And then the wind fields were blended with the reanalyzed synoptic-scale wind fields for a wave model.Wave fields were simulated using WAM4.5 with adjustment of C_d for gust of winds and bottom friction for the study area.Thus the accuracy of simulations is considerably enhanced,and the computed results are also in better agreement with measured data than before.It is found that the extremely high waves evolved as a result of the superposition of distant large swells and high wind seas generated by strong winds from the front/right quadrant of the typhoon track.As the typhoon moved at a speed a little slower than the dominant wave group velocity in a consistent direction for two days,the wave growth was significantly enhanced by strong wind input in an extended fetch and non-linear interaction.

Simulation of Typhoon-Driven Waves in the Yangtze Estuary with Multiple-Nested Wave Models

Typhoon-generated waves are simulated with two numerical wave models, the SWAN model for the coastal and Yangtze Estuary domain, nested within the WAVEWATCHIII （WW3） for the basin-scale East China Sea domain. Typhoon No. 8114 is chosen because it was very strong, and generated high waves in the Estuary. WW3 was implemented for the East China Sea coarse-resolution computational domain, to simulate the waves over a large spatial scale and provide boundary conditions for SWAN model simulations, implemented on a fine-resolution nested domain for the Yangtze Estuary area. The Takahashi wind model is applied to the simulation of the East China Sea scale （3-hourly） and Yangtze Estuary scale （1-hourly） winds. Simulations of significant wave heights in the East China Sea show that the highest waves are on the right side of the storm track, and maxima tend to occur at the eastern deep-water open boundary of the Yangtze Estuary. In the Yangtze Estuary, incoming swell is dominant over locally generated waves before the typhoon approaches the Estuary. As the typhoon approaches the Estuary, wind waves and swell coexist, and the wave direction is mainly influenced by the swell direction and the complex topography.

Effect of the drag coefficient on a typhoon wave model

The effect of the drag coefficient on a typhoon wave model is investigated.Drag coefficients for Pingtan Island are derived from the progress of nine typhoons using COARE 3.0 software.The wind parameters are obtained using the Weather Research and Forecasting model.The simulation of wind agrees well with observations.Typhoon wave fields are then simulated using the third-generation wave model SWAN.The wave model includes exponential and linear growths of the wind input,which determine the wave-growth mode.A triple triangular mesh is adopted with spatial resolution as fine as 100 m nearshore.The SWAN model performs better when using the new drag coefficient rather than the original coefficient.

Bimodality and growth of the spectra of typhoon-generated waves in northern South China Sea

Buoy-based observations of wave spectra during the passage of three typhoons in the northern South China Sea are examined.Though most spectra of mature typhoon-generated waves are unimodal,double-peaked spectra account for a significant proportion during the growing and decaying stages.This is due either to the superposition of swells on local wind waves or to the mechanism of nonlinear interaction between different wave components.The growth rate of energy density is an effective way to predict spectrum variation.The dominant wave direction depends on the location of the typhoon center to the site,but the direction spread shows no regularity in distant regions.In this study,a new six-parameter spectral formula is proposed to represent doublepeaked spectra and is shown to provide a better fit than previous models.The theoretical relationship between shape parameter and spectral width is still applicable to each peak.The characteristics of the variations of spectral parameters are analyzed.It is demonstrated that the spectral parameters are not only related to the typhoon intensity and typhoon track,but also have strong intercorrelations.Moreover,the growth relation between significant wave height and significant wave period is obtained to fit the typhoon-generated waves.

Observed Near Inertial Waves in the Wake of Typhoon Linfa(2015) in the Northern South China Sea

This study examined the characteristics and vertical propagation of near inertial waves(NIWs)induced by Typhoon Linfa(2015),based on in situ observations conducted southeast of Dongsha Islands in the South China Sea.The results demonstrate that the near inertial currents induced by Linfa had velocities up to 35 cm s^-1 in the mixed layer and 20 cm s^-1 in the ocean interior.The near inertial currents were polarized with predominantly clockwise-rotating components,the magnitudes of which were about 10 times larger than the counter-clockwise rotating components.The energy density spectrum showed that the emergence of NIWs resulted in energy redistribution from the diurnal band to the near inertial band.The wavenumber spectrum and the downward/upward current decomposition demonstrated that the NIWs and energy flux propagated mainly downward.The estimated vertical phase velocity and group velocity are 1.44 and 0.48 m h-1,respectively,corresponding to a vertical wavelength of 49.7 m.The e-folding time scale was 7.5 d based on the near inertial kinetic energy in the ocean interior.We found no obvious wave–wave interaction during the decay process of the NIWs.The frequency was blue-shifted,being 0.03 f0 higher than the local inertial frequency,which was caused by the background vorticity.The normal mode analysis suggests that the higher mode plays a dominant role in the propagation stage of the NIWs.

Comparison Study on Wind Input and Whitecapping Dissipation Expressions in Numerical Simulation of Typhoon-Generated Waves

In order to investigate the effect of wind input and whitecapping dissipation on the simulation of typhoon-waves, three experiments are conducted with the latest version of SWAN （Simulating WAves Nearshore） model. The three experiments adopt the Komen, Janssens, and Westhuysen expressions for wind input and whitecapping dissipation, respectively. Besides the above-mentioned source tems, other parameterization schemes in these experiments are the same. It shows that the experiment with the Westhuysen expression result in the least simulation errors while that with the Janssens expression has the most. The results from the experiments with Komen and Westhuysen expressions show that the differenees in significant wave height （SWH） have a good correlation with the differences in dissipation energy caused by whiteeapping. This indicates that the whitecapping dissipation source term plays an important role in the resultant differences of the simulated SWH between the two experiments.

The effect of wave-induced radiation stress on storm surge during Typhoon Saomai(2006)

The effects of wave-induced radiation stress on storm surge were simulated during Typhoon Saomai using a wave-current coupled model based on ROMS （Regional Ocean Modeling System） ocean model and SWAN （Simulating Waves Nearshore） wave model. The results show that radiation stress can cause both set-up and set-down in the storm surge. Wave-induced set-up near the coast can be explained by decreasing significant wave heights as the waves propagate shoreward in an approximately uniform direction; wave-induced set-down far from the coast can be explained by the waves propagating in an approximately uniform direction with increasing significant wave heights. The shoreward radiation stress is the essential reason for the wave-induced set-up along the coast. The occurrence of set-down can be also explained by the divergence of the radiation stress. The maximum wave-induced set-up occurs on the right side of the Typhoon path, whereas the maximum wave induced set-down occurs on the left side.