Resource assessment as well as characterisation of site climatologies for the design of Marine Energy Converters requires data bases allowing an accurate description of the environmental forcing, especially waves and sea-states, on a high resolution grid. As a support to its research activities related to the development of marine renewable energies, Ifremer is building a specific hindcast data set for the assessment of sea-states climatologies. The main features of this database, built running an up-to-date configuration of the WaveWatch III ® wave model on an unstructured grid extending from the South of the North Sea to the Bay of Biscay are presented here. Attention is given to the parameterization and forcing as well as the specific output data sets and validation processes.

Storm surge modeling and forecast are the key issues for coastal risk early warning systems. As a general objective, this study aims at improving high-frequency storm surge variations modeling within the PREVIMER system (www.previmer.org), along the French Atlantic and English Channel coasts. The paper focuses on (1) sea surface drag parameterization and (2) uncertainties induced by the meteorological data quality. The modeling is based on the shallowwater version of the model for applications at regional scale (MARS), with a 2-km spatial resolution. The model computes together tide and surge, allowing properly taking into account tide-surge interactions. To select the most appropriate parameterization for the study area, a sensitivity analysis on sea surface drag parameterizations is done, based on comparisons of modeled storm surges (extracted with a tidal component analysis) with four tidal gauges, during four storm events, and over about 7.5 years, where the observed water level is processed in the same way as the modeling results. The tested drag parameterizations are a constant one, as reported by Moon et al. (J Atmos Sci 61: 2321-2333, 2007, Makin (BoundLayer Meteorol 115: 169-176, 2005), and Charnock (J Roy Meteor Soc 81: 639-640, 1955). Charnock's parameterization, either constant with high value (0.022) or relying on a full statistical description of the sea state, enables to improve storm surges forecast with peak errors 10 cm smaller than those computed with the other drag coefficient formulations. The impact of the meteorological forcing quality is evaluated over January 2012 from the comparison between surges modeled with different meteorological data (ARPEGE, ARPEGE High Resolution and AROME) and observations. For event time scale, storm surge computation is highly improved with ARPEGE High Resolution data. For month time scale, statistics of model accuracy are less sensitive to the choice of meteorological forcing. As a conclusion, the Charnock's parameterization is advised to model storm surges on the French Atlantic and English Channel coasts, whereas the quality requirements regarding meteorological inputs depend on the time scale of interest. Within the PREVIMER system, aiming at forecasting events, ARPEGE High Resolution data are used.

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Strong winds may be biased in atmospheric models. Here the European Centre for Medium-range Weather Forecasts (ECMWF) coupled wave-atmosphere model is used (i) to evaluate strong winds against observations, and (ii) to test how alternative wind stress parametrizations could lead to a more accurate model. For the period of storms Kaat and Lilli (23-27 January 2014), we compared simulated winds with in situ -moored buoys and platforms -and satellite observations available from the North Atlantic. Five wind stress parametrizations were evaluated. The first result is that moderate simulated winds (5-20 m s −1 ) match with all observations. However, for strong winds (above 20 m s −1 ), mean differences appear, as much as −7 m s −1 at 30 m s −1 . Significant differences also exist between observations, with buoys and Advanced Scatterometer ASCAT-KNMI generally showing lower wind speeds than the platforms and other remote-sensing data used in this study (AMSR2, ASCAT-RSS, WindSat, SMOS and JASON-2). Buoy and ASCAT-KNMI winds are likely to underestimate the real wind speed. It is difficult to conclude which dataset should be used as a reference. The second result is that common wave-age dependent parametrizations produce unrealistic drags and are not appropriate for coupling, whereas a newly empirically adjusted Charnock parametrization leads to higher winds compared to the default ECMWF parametrization. This proposed new parametrization may lead to more accurate results in an operational context.