Eventos de alturas de olas extremas en el NO de España: Un enfoque combinado de múltiples sensores y modelos

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Extreme Wave Height Events in NW Spain: A Combined Multi-Sensor and Model Approach

The Galician coast (NW Spain) is a region that is strongly influenced by the presence of low pressure systems in the mid-Atlantic Ocean and the periodic passage of storms that give rise to severe sea states. Since its wave climate is one of the most energetic in Europe, the objectives of this paper were twofold.

The first objective was to characterize the most extreme wave height events in Galicia over the wintertime of a two-year period (2015–2016) by using reliable high-frequency radar wave parameters in concert with predictions from a regional wave (WAV) forecasting system running operationally in the Iberia-Biscay-Ireland (IBI) area, denominated IBI-WAV.

The second objective was to showcase the application of satellite wave altimetry (in particular, remote-sensed three-hourly wave height estimations) for the daily skill assessment of the IBI-WAV model product.
Special attention was focused on monitoring Ophelia—one of the major hurricanes on record in the easternmost Atlantic—during its 3-day track over Ireland and the UK (15–17 October 2017).

Overall, the results reveal the significant accuracy of IBI-WAV forecasts and prove that a combined observational and modeling approach can provide a comprehensive characterization of severe wave conditions in coastal areas and shows the benefits from the complementary nature of both systems.

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Estimación de la bondad del ajuste métrico de las medidas a largo plazo del oleaje derivado del Seasonde en el NO de España

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Long-term skill assessment of SeaSonde radarderived wave parameters in the Galician coast (NW Spain)

A long-term multi-parameter skill assessment of a 5-MHz Coastal Ocean Dynamics Applications Radar (CODAR) SeaSonde High-Frequency radar (HFR) network deployed along the Galician Coast (NW Iberian Peninsula) was attempted for 2014–2016. To this aim, wave estimations from two HFR sites, obtained directly by the CODAR radar proprietary software, were independently validated against hourly in situ observations from two moored buoys for two different periods. The accuracy assessment of significant wave height (Hs) revealed a consistent agreement with Pearson´s
correlation coefficients (r) above 0.75 and normalized root mean squared errors below 0.4. An overall slight overestimation of Hs radar estimations was evidenced, likely due to spurious contributions to the directional spectra.

The seasonal analysis revealed that the performance of this low mono-frequency radar was more precise for high-sea states during wintertime, whereas the quality and availability of radar data decreased under summer less energetic conditions, in accordance with previous works. In the case of the centroid wave period, HFR performance was consistent through the different years, with r values emerging in the range
of 0.61–0.74. The directional accuracy was moderately good, with NW and W-NW as predominant sectors. Despite r values above 0.74, a tendency for CODAR HFR-derived incoming mean wave direction to be aligned more perpendicular to the coast compared to offshore in situ data was also observed. Furthermore, the relationship between the North Atlantic Oscillation (NAO) and HFR wave estimations was explored. A subtle but statistically significant connection was found, with Hs and centroid wave period being positively correlated with NAO daily index.

Complementarily, the skill of the Galician HFR system was evaluated under positive and negative NAO conditions in order to elucidate whether the radar accuracy is or is not NAO-phase dependent. No substantial differences could be found for each of the three parameters analysed as HFR accuracy remained mostly unaffected by swings in the NAO index. Finally, it can be concluded that properly treated CODAR radar-derived wave estimations
can be potentially employed for operational coastal monitoring across a wide range of sea states.

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