These data are combined with the previous wave forecast, in a process called data assimilation, to provide the initial conditions for the next forecast. Satellite-based instruments, such as altimeters, provide data on significant wave height, a widely used sea-state parameter which is roughly the average height of the highest one third of waves. The wave model then simulates how the wave spectrum evolves in space and time by representing how the wind generates waves, how different waves interact with each other, and how wave energy gradually dissipates. Waves are also divided into those generated by local wind (wind sea waves) and waves which have travelled away from where they were generated (swell). The surface wave field is simplified and represented by a spectrum of waves according to frequency (or wavelength) and direction of propagation. It covers both the open ocean and coastal waters. This is too complex to model explicitly, so the ECMWF ocean wave model (ECWAM) is based on a statistical description of surface waves. The ocean surface wave field consists of a highly complex combination of waves with different heights, wavelengths and directions.
In ECMWF’s Integrated Forecasting System (IFS), the wave model is coupled to an atmospheric model and an ocean model so that all relevant interactions can be taken into account and all predictions are consistent with each other. The ocean waves in turn influence the atmosphere above and the ocean below, so it is important to include their effects in weather forecasts.
The waves can travel thousands of kilometres from where they originated. The ocean waves that affect sea conditions are primarily generated by surface winds. Such forecasts can help to save lives and limit the damage caused by severe storms. Shipping, fisheries, offshore operations, coastal protection and marine recreation are all strongly dependent on weather and sea conditions and require marine weather forecasts extending to the limit of the medium-range forecasting period (up to ten days ahead). (andrej67/iStock/Getty Images) Why is ocean wave forecasting important? Waves interact with conditions in the atmosphere and the ocean.
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