Evaluation of Operational Wave Forecasts for the Northeastern Coast of Taiwan

  • Author(s): Beng-Chun Lee, Hwa Chien, Hao-Yuan Cheng, and Ming-Da Chiou
  • DOI:

    10.3319/TAO.2009.06.03.02(IWNOP)

  • Keywords: Regional wave forecast, Man-machine mix system, SWAN wave model

 

Abstract

An operational regional wave forecasting system was established to fulfill the demands of maritime engineering applications on the northeastern coast of Taiwan. This Mixed system consisted of a nested SWAN numerical wave model and experienced marine meteorologists who were sent to the construction site as the in situ predictors to validate output from the numerical model so as to improve the forecasting accuracy.

This paper will offer an evaluation of this regional wave forecasting system. Records of hourly forecasts from June to October 2004 obtained by direct numerical model and the in situ predictors' modifications are comprehensively compared. First, the nested SWAN is verified with the observational data. The Alves and Banner's (2003) wave energy dissipation term is adopted for better wave period simulation. The error analysis is then carried out to discriminate the performances of the system to the direct numerical model. It is found that the in situ predictors provided invaluable modifications which reduced the root mean square error by 30% to the deviated model outputs as well as the quality of the forecasted wind fields used to drive the wave model played key role to the wave prediction. About 20% of the errors of +3 days wave predictions were incurred by the uncertainties of wind fields. As the miss-predicted trajectory of typhoon centers exceeding 90 km, the wave predictions would not be valid, and the benefits from in situ predictors became marginal. Finally, land and sea breezes are important factors in regional wave forecasts for engineering applications as both can induce diurnal wave heights oscillations, which is not destructive, but crucial to the quality of marine engineering. As the scale of the land/sea breeze is not resolved in the operational forecasted wind fields issued by Central Weather Bureau. Currently, the implementation of in situ predictors is necessary.

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