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This figures show an example of the effects of currents on the wave heights. Waves are also affected by sea ice and icebergs, and all operational global wave models take at least the sea ice into account. Ocean currents can also be important, in particular in western boundary currents such as the Gulf Stream, Kuroshio or Agulhas current, or in coastal areas where tidal currents are strong. The most common sources of errors in wave model results are the errors in the wind field. Ī more critical input is the "forcing" by wind fields: a time-varying map of wind speed and directions. In practice, many forecasting system rely only on the previous forecast, without any assimilation of observations. An analysis of the sea or ocean can be created through data assimilation, where observations such as buoy or satellite altimeter measurements are combined with a background guess from a previous forecast or climatology to create the best estimate of the ongoing conditions. Differences in model results arise (with decreasing order of importance) from: differences in wind and sea ice forcing, differences in parameterizations of physical processes, the use of data assimilation and associated methods, and the numerical techniques used to solve the wave energy evolution equation.Ī wave model requires as initial conditions information describing the state of the sea. Wind wave models are used in the context of a forecasting or hindcasting system. Improvements included two-way coupling between wind and waves, assimilation of satellite wave data, and medium-range operational forecasting. The wave modeling project (WAM), an international effort, led to the refinement of modern wave modeling techniques during the decade 1984-1994. Third generation models explicitly represent all the physics relevant for the development of the sea state in two dimensions. They included the “coupled hybrid” and “coupled discrete” formulations. Second generation models, available by the early 1980s, parameterized these interactions. įirst generation wave models did not consider nonlinear wave interactions. The 1970s saw the first operational, hemispheric wave model: the spectral wave ocean model (SWOM) at the Fleet Numerical Oceanography Center. The first numerical model based on the spectral decomposition of the sea state was operated in 1956 by the French Weather Service, and focused on the North Atlantic. This approach allowed to make combined forecasts of wind seas and swells. For forecasting purposes, it was realized that the random nature of the sea state was best described by a spectral decomposition in which the energy of the waves was attributed to as many wave trains as necessary, each with a specific direction and period. ĭuring the 1950s and 1960s, much of the theoretical groundwork necessary for numerical descriptions of wave evolution was laid. Alternatively, the swell part of the state has been forecasted as early as 1920 using remote observations. Early forecasts of the sea state were created manually based upon empirical relationships between the present state of the sea, the expected wind conditions, the fetch/duration, and the direction of the wave propagation.