Silvia Piedracoba

Accuracy assessment of high frequency radar current measurements in the Strait of Gibraltar

An assessment of accuracy of a three site short-range (27 MHz) CODAR SeaSonde HF radar network deployed in the Strait of Gibraltar is attempted by comparing its surface current estimates with measurements from a moored point current meter. Radial and total current vectors are compared for a 47 day period from 19 October to 4 December 2013, yielding angular offsets, root mean square errors and correlations in the range 2ͦ–30ͦ, 8–22 cm s-1 and 0.31–0.81, respectively. Statistics improve when the measured antenna pattern is used, except at one radar site. A self-consistency check in overwater baseline reveals that the dominant source of velocity differences is HF radar variance error.

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, denominatedIBI-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.

Ocean model skill assessment in the NW Mediterranean using multi-sensor data

ABSTRACT This paper showcases the one year-long (2014) multi-parameter skill assessment of Iberia-Biscay-Ireland (IBI) operational ocean forecasting system. The investigation is focused on a specific subdomain in the Northwestern Mediterranean where several observational networks encompassing both in situ and remote sensing instruments are available. This region is relevant since it includes two harbours and a marine protected area, the Ebro River Delta. Class-1 and class-2 skill metrics are used in concert to quantitatively evaluate the quality of hourly IBI surface fields. The impact of riverine discharges on the coastal circulation is investigated by comparing the signal of the Ebro River freshwater outflow in both observed (high-frequency radar (HFR)) and modelled (IBI) current maps. The ability of the HFR and IBI to detect the presence of coastal eddies is also qualitatively estimated by calculating surface vorticity maps. According to the results, basic circulation features are statistically reproduced by IBI in reference to mean and variance, despite some model drawbacks in terms of reduced energy content in surface currents. IBI has proven to be a robust model solution in the study area, able to act as a consistent large-scale ‘father’ system in future downscaling approaches by providing coherent open boundary conditions to nested high-resolution coastal models.

Rapid response to coastal upwelling in a semienclosed bay

Bays/estuaries forced by local wind show bidirectional exchange flow. When forced by remote Q3 wind, they exhibit unidirectional flow adjustment to coastal sea level. Acoustic Doppler Current Profiler observations over 1 year show that the Ria de Vigo (Iberian Upwelling) responds to coastal wind events with bidirectional exchange flow. The duration of the upwelling and downwelling events, estimated from the current variability, was ~3.3 days and ~2.6 days, respectively. Vectorial correlations reveal a rapid response to upwelling/downwelling, in which currents lag local wind by <6 h and remote wind by <14 h, less than the Ekman spinup (17.8 h). This rapidity arises from the ria’s narrowness (nonrotational local response), equatorward orientation (additive remote and local wind responses), depth greater than the Ekman depth (penetration of shelf circulation into the interior), and vertical stratification (shear reinforcing shelf circulation). Similar rapid responses are expected in other narrow bays where local and remote winds act together and stratification enhances bidirectional flow.