Numerical Study Of Waves Characteristics In The Yellow Sea And East China Sea Under Typhoon CHAN-HOM

As a strong weather phenomenon,typhoon seriously affect the economic construction and the safety of lives and properties by causing strong winds,huge waves and flooding in coastal areas.Wave forecasting has been a priority for marine research.Because of the difficulty of continuous observation,numerical model is often used to realize the research of typhoon waves.In this study,the Simulating WAves Nearshore(SWAN)model and the Regional Ocean Modeling System(ROMS)within the COAWST(Coupled-Ocean-Atmosphere-WaveSediment Transport)modeling system are applied to study the response of the wave field under Typhoon CHAN-HOM(No.201509)in the Yellow Sea and East China Sea.By comparing the modeled results with buoy data and the Jason-2 altimeter,the accuracy of the simulation is validated.Several sensitivity experiments are carried out to examine the difference of simulation results under different terrain data(ETOPO1,ETOPO2,GEBCO),coupled and uncoupled model(SWAN+ROMS,SWAN)and different physical parameterization schemes(wind energy input and white-capping,friction dissipation).It is found that the modeled results using GEBCO terrain data are more accurate and stable.Owing to the strong near inertial current induced by typhoon,it is found that the wave-current interaction is significant near the center of typhoon.The doppler effect cause distinct change of significant wave height on both sides of the heading direction of the typhoon.When the typhoon intensity is high,the difference of significant wave height caused by current is greater than 1 meter.The difference of the significant wave height between different wind energy input and white-capping schemes can be close to 0.4 meter,while the difference between different bottom friction schemes can be close to 1 meter.According to the sensitivity experiments,we obtain a suitable scheme for wave simulation under Typhoon CHAN-HOM.Wave fields show different characteristics under the process of typhoon with different stages.In the right front quadrant of the heading direction,the wind vectors are aligned with the heading direction of typhoon,and waves experience an extended fetch.The significant wave height increases significantly.While in the left quadrant,the wave direction is opposite to the heading direction of typhoon,leading to shorter fetch and thus the decrease of significant wave height.The asymmetry of wave fields is positively correlated with typhoon intensity.At the right front quadrant of typhoon heading direction,the wave directional spectrum is mainly characterized by unimodal,and the propagation direction is narrow.The peak frequency is within 0.1 Hz,and the dominant wave propagates to the northwest or to the north.However,in the left and back quadrants of heading direction,the directional spectrum shows bimodal or multimodal characteristics.The spectrum is wide and is tilted from low frequency to high frequency.The peak frequency is near 0.1 Hz.Under typhoon with strong intensity,the influence of near inertial current on wave energy is more significant,and the wave energy decreases more obviously in the right front quadrant.In our study range(3-4 times maximum wind speed radius),the significant wave height in the right front quadrant is affected by the extended fetch and increases basically with the distance to the typhoon center,while the variation in other quadrants is relatively complicated.