THE EFFECT OF ASSIMILATING ERS-1 FAST DELIVERY WAVE DATA INTO THE NORTH-ATLANTIC WAM MODEL

The launch of the European ERS satellites has provided a new source of wave information that is particularly suitable for use in improving w ave forecasts in the open ocean. We have implemented and tested a simp le system for assimilating corrections to model wave fields produced b y the WAM model, where the corrections are derived from inverted synth etic aperture radar (SAR) image spectra from ERS-1, Corrections are ap plied to significant wave height, mean period and direction for wave m odes that are detectable in both the model and the SAR data. The syste m has been tested in a storm situation and in moderate conditions usin g buoy data and altimeter data, as well as SAR observations for verifi cation. Overall, it is demonstrated that the net effect of assimilatin g SAR data is beneficial but very small. The small impact is due at le ast partly to relatively small spatial and temporal coverage of the SA R wave mode data. Locally larger impacts were found in the storm situa tion in individual cases where SAR observations were collocated with i ndependent buoy observations.