Sequential assimilation in the wind wave model for simulations of typhoon events around Taiwan Island

We investigate the effect of data assimilation in the Wind Wave Model (WWM, Hsu et al., 2005) for wind wave simulations of typhoon events using an Optimal Interpolation (OI) method in the coastal waters of Taiwan. The main point of the present study is that the assimilation is conducted for typhoon events with short-time periods around an island. Five real typhoon events were used for numerical assimilation experiments with different combinations of the key parameters: the correlation length, the ratio of the errors between the observation and the prediction, and the number of measuring stations. The retrieved wind velocity is obtained using the wave energy growth curve computed from the WWM. The wave energy dissipation function suggested by Makin and Kudryavtsev (1999) was adopted in the data assimilation. This study shows that assimilation can improve the initial performance of the wave model, but it becomes insignificant after about 12 h. In summary, the OI approach is shown to be a reliable assimilation scheme for the WWM applied to typhoon events in the coastal waters of Taiwan Island.