A wave prediction system for real-time sea state forecasting

The considerable increase in requirements for sea state forecasts in recent years has led to development of a numerical wave forecasting system in the Meteorological Office. This is based on a wave prediction model which combines the advantages of the parametric technique in predicting a growing wind-sea with those of a discrete spectral model in the swell regime. This is done using a discrete model by parametrizing the nonlinear interactions term in the energy balance equation in a way that reproduces the behaviour of the parametric model. The main difficulty with the method is in the separation of wind-sea and swell required to do this. Propagation of wave energy is performed using an accurate form of the Lax-Wendroff integration scheme. A two-term representation of wave growth is used whilst dissipation is modelled by an explicit whitecapping mechanism. Shallow water effects are included by representations of shoaling, refraction and bottom friction. The operational numerical atmospheric model at the Meteorological Office provides the wind input. An extensive program of evaluation has shown that the results provide high quality guidance with 24-hour forecasts of wave height having a r.m.s. error ranging from 0·6 m in the southern North Sea to 1·0 m east of the Shetlands.

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