A spectral model for the sea-state with explicit forcing terms

A spectral ocean wave model with explicit representations of the identified physical source terms is described. The model has the ability to represent the evolution of the wave spectrum effectively without the need for a very short integration timestep. This is achieved by incorporating a simple parameterisation for the weakly nonlinear wave-wave interactions and using a predictor step to estimate the integral parameters which govern the form of this function. The model was tested over a number of ideal situations and conformed well to the data. It also performed comparably to the third-generation WAM model. In field trials the model was driven by winds derived from numerical weather prediction model initialisations via a diagnostic marine boundary layer model. The wave estimates were compared with data from a Waverider buoy at a site exposed to the Southern Oceans. Significant wave heights were modelled well with a root-mean-square error of 0·9m and a scatter index of 0·24. Frequency characteristics produced poorer results but similar to other operational models, i.e. frequency was over-estimated. Comparisons with significant wave heights from the GEOSAT radar altimeter gave a spatial measure of the model's performance which was similar to the temporal measure from the Waverider buoy data.