Accuracy of the modelled wind and wave fields in enclosed seas

The meteorological model of the European Centre for Medium-RangeWeather Forecasts, run with different resolutions, has been used to explore, with a number of numerical experiments, the underestimate of wind speeds and wave heights found in enclosed basins. Comparisons have been made between the results from the different runs, and also against satellite and buoy data.

It is found that the error depends on fetch, i.e. on the distance from the closest land from which the wind is blowing. Large errors are found at short fetches (order of 100 km), gradually decreasing with the distance from the coast. The error is larger and more persistent for waves. Increasing the resolution leads to an improvement of the results. However, the bias does not disappear at the highest resolution we have used (about 25 km).

Experiments with the single-point version of the meteorological model do not suggest that a slow development of the marine boundary layer is the main reason for the underestimate of the wind speeds.With respect to the mean orography, the use of envelope orography leads to a substantial increase of the marine wind speeds in the area affected by land.