Numerical Analysis Of Storm Surge In Taiwan Strait

The process of two storm surges caused by typhoon FANAPI of2010and SEPATof2007respectively when translating Taiwan Strait were simulated based on FVCOM,using wind field generated using typhoon model by Willoughby as atmospheric forcing.The model results were validated by the measured data and the response of water level andcurrent field to the typhoon was analyzed, and the results showed that the simulated waterlevel of the storm surge matches reasonably well with measurements, which verifies thatthe coastal water level is mostly caused by local wind. The residual water elevation wasinfluenced by typhoon FANAPI in most area of Taiwan Strait. The mainland coast, whichlay in the windward side, has the elevation up to more than2m. The setup areacaused by typhoon Sepat is on the north coast of mainland and the maximum setup ismore than3m. The south coast of mainland which is in offshore wind area occurssetdown. The elevation water is mostly influenced by wind and topography.Characteristics of the modelled wind-driven surface currents are consistent with thoseof Ekman drift currents. During typhoon FANAPI, precursor waves of the stormsurge in mainland coastal regions have an amplitude of20-30cm, while aftershock isnot obvious, but during typhoon SEPAT, precursor waves is not obvious andaftershock last long. Averaged wind-driven surface currents had a direction parallel tothe coastline in the coastal regions and had larger velocities. During typhoon FANAPI, anon-closed counterclockwise current was formed in the center of the strait, and thedirection of the current is same with that of the strongest wind field of the typhoon duringtranslating Taiwan Strait. During typhoon SEPAT, a counterclockwise current was formedin north of Taiwan Strait and the flow velocity gradually decreases from the inside tothe outside, having the same characteristic with wind field of the typhoon beforelandfall. Averaged wind-driven surface currents are related to local wind and windlasting time.A set of sensitivity experiments are carried out in part four in order to study the impact of three different parameters of typhoon, radius to maximal wind(RMW),maximal wind(MW) and translation speed(TS). The results show: with the decreaseof typhoon’s translation speed, the stations located in the windward area during theprocess of typhoon have higher biggest setup, while the stations located in theleeward area have lower biggest setdown; with the increase of radius to maximalwind, the area effected by typhoon expands, and amplitude of water elevationincreases slightly. Stations located within radius to maximal wind have lower waterelevation with with the increase of radius to maximal wind, while stations locatedwithout radius to maximal wind have higher water elevation. When stations arelocated near the radius to maximal wind, the change of water elevation is complex.With the increase of typhoon’s maximal wind, amplitude of water elevation increasesobviously, and the biggest setup of the stations increase as well. The stations locatedin the northeast of typhoon center is in the windward area, whose increae trendbecomes bigger with the increase of typhoon’s maximal wind. The stations located inthe southwest of typhoon center is in the leeward area, whose increae trend becomessmaller with the increase of typhoon’s maximal wind.