Operational wave forecast model upgrade

To ensure the highest possible performance at MetOcean Solutions, we continuously improve our models to match state-of-the-art science. Our science team is currently working on implementing the Spherical Multiple-Cell (SMC) grid in the global wave model WAVEWATCH III. SMC grids are unstructured, supporting flexible domain shapes and variable resolutions. 

"SMC is a multi-resolution grid with refinement in coastal areas and around islands, which are generally not well represented in a standard regular grid,” explains MetOcean physical oceanographer Dr Emilio Echevarria. “With this implementation, we are not only improving wave forecasting from our global models, but also the boundary conditions for our high-resolution nests using SWAN wave models.” 

Figure shows a comparison of significant wave height (Hs) from a regular grid (left) and SMC grid (right) against the NDBC buoy observations (line graph). One of the key improvements of SMC grid is a better representation of the wave field in the shadow of islands, while the regular grid accounts for it in a simplified way.

The configuration uses a SMC grid with refined cell scales reducing from 40km in the open ocean to up to either 20km or 10km for areas with depths <70 m and in areas of interest. 

“We have carefully validated the significant wave height against satellite altimeter data,” continues Emilio. “Comparison against satellite altimeters and in-situ wave observations showed consistent improvements in our models across all major areas.” 

The resulting improvements are shown in the figure below. Using satellite observations to quantify these gains, the figure shows the root-mean-square-error of wave height (i.e. model performance), scatter index (SI), and correlation coefficient, commonly used measurements of wave model skills. 

Validation of significant wave height against satellite altimeter measurements. Top: Difference in root-mean-square error (RMSE). A negative value (blue) indicates a lower RMSE, higher accuracy, for the SMC grid compared to the regular grid. Middle: Difference in scatter index, with negative values indicating higher accuracy for the SMC case. Bottom: Difference in correlation coefficient, with positive values (red) indicating a higher correlation/accuracy with the SMC grid.

We are improving the overall model accuracy through a better description of coastline features, island masks and changes in depth - all of which have a major impact on the wave climate in nearshore areas - whilst retaining model efficiency. An additional benefit is to enable good quality forecasts in certain areas without requiring nested regional models. 

For more information about MetOcean’s operational forecast contact us at enquiries@metocean.co.nz