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Comparison of altimetry wave and wind data with model and buoy data

Claus SĂžlvsteen(1) and Carsten Hansen(1)

(1) Royal Danish Administration of Navigation and Hydrography, Overgaden o. Vandet 62 B, 1023 Copenhagen, Denmark

Abstract

A quality controlled dataset of significant wave heights (SWH) and wind speeds based on ERS-2 and Topex/Poseidon (T/P) altimetry from the period 1999-01-01 to 2000-02-29 has been compared with buoy observations of significant wave height (HS) and model forecasts of HS and wind velocity. The examined area covers four sub-areas: : the western part of the North Sea, the eastern part of the North Sea including the Skagerrak, the Kattegat and the western part of the Baltic Sea. The wave models are OSW (a commercial product of DHI Water&Environment based on the WAM model) and Wave Watch III (WW3 of H. Tolman, NOAA/NCEP). Both models have been run with a standard parameterisation and both are forced by the forecasted 10 m wind. For the wind forecast the first 6 hours of the model Hirlam E15 of the Danish Meteorological Institute have been used. The buoy observations have been performed near the west coast of Jutland and the north-west coast of Germany. Small correction algorithms have been applied to satellite SWH data, while satellite wind data are uncorrected.

The analysis shows that SWHs and wind speeds from ERS-2 and T/P are consistent and may be merged together in the comparison with model data and buoy observations.

Wave heights of the satellites agree well with the WW3 model, and the WW3 wave heights agree well with the buoy observations. OSW wave heights tend to be about 20% higher than satellite wave heights. These results are independent of the sub-area in consideration, but varies slightly over the seasons.

Satellite winds are about 9% lower than Hirlam winds (15-20% for high wind speeds). This result is slightly dependent on the choice of sub-area (for the Kattegat Hirlam forecasts and altimetry winds differ more than for the other areas). There are seasonal variations in the wind comparisons, especially for the low wind speeds.

Based on these observations it is concluded that altimetry SWH and wind speeds from the two satellites support each other well in any comparison with other data types. Satellite SWHs may be a valuable source for wave model validation and/or assimilation, while the wind speeds derived from satellite altimetry differ systematically from the wind model.

 

Full paper

 

                 Last modified: 07.10.03