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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.

Abstract. In this work, a multi-parameter inter-comparison of diverse ocean forecast models was conducted at the sea surface ranging from global to local scales in a two-phase stepwise strategy. Firstly, a comparison of CMEMS GLOBAL and the nested CMEMS IBI regional system was performed against satellite-derived and in situ observations. Results highlighted the overall benefits of both the GLOBAL direct data assimilation in open water and the increased horizontal resolution of IBI in coastal areas. Besides, IBI (Iberia–Biscay–Ireland) proved to capture shelf dynamics by better representing the horizontal extent and strength of a river freshwater plume, according to the results derived from the validation against in situ observations from a buoy moored in NW Spain. Secondly, a multi-model inter-comparison exercise for 2017 was performed in the Strait of Gibraltar among GLOBAL, IBI, and SAMPA (Sánchez-Garrido et al., 2013) high-resolution coastal forecast systems (partially nested to IBI) in order to elucidate the accuracy of each system to characterize the Atlantic Jet (AJ) inflow dynamics. A quantitative validation against hourly currents from high-frequency radar (HFR) highlighted both the steady improvement in AJ representation in terms of speed and direction when zooming from global to coastal scales through a multi-nesting model approach and also the relevance of a variety of factors at local scale such as a refined horizontal resolution, a tailored bathymetry, and a higher spatio-temporal resolution of the atmospheric forcing. The ability of each model to reproduce a 2 d quasi-permanent full reversal of the AJ surface inflow was examined in terms of wind-induced circulation patterns. SAMPA appeared to better reproduce the reversal events detected with HFR estimations, demonstrating the added value of imposing accurate meteorologically driven barotropic velocities in the open boundaries (imported from the NIVMAR (Álvarez-Fanjul et al., 2001) storm surge model) to take into account the remote effect of the atmospheric forcing over the entire Mediterranean basin, which was only partially included in IBI and GLOBAL systems. Finally, SAMPA coastal model outputs were also qualitatively analysed in the western Alboran Sea to put in a broader perspective the context of the onset, development, and end of such flow reversal episodes.

Abstract. The influence of targeted observations on shortrange forecasts is tested over two different periods of PRE-VIEW (2008) and MEDEX (2009) data targeting field campaigns for a set of Mediterranean high-impact weather events. As targeted observations we have used not only extra radiosondes, but also enhanced satellite data observed in singular vector (SV)-based sensitive regions. Three parallel observing system experiments, based on the High-Resolution Limited-Area Model (HIRLAM) data assimilation and forecast system, have been conducted. Forecasts of the three experiments have been assessed using both verifying analyses for upper-air fields, and surface observations for several meteorological parameters. Furthermore, quantitative precipitation forecasts (QPF) have been objectively verified using the novel feature oriented Structure-Amplitude-Location (SAL) method.The results obtained show that extra radiosondes have an overall positive impact on the forecasts (average improvement of all upper-air variables and vertical levels studied is 3.6 %). When in addition to extra radiosonde data also enhanced satellite data are assimilated, the overall forecast skill is almost doubled. However, a distinct behaviour is found between the PREVIEW and MEDEX cases. While for MEDEX cases the improvement is slight, for PREVIEW cases the improvement is significant (average improvements of 1.7 % and 8.9 %, respectively, for the experiment with enhanced satellite data). It is suggested that this is due to the location of the target areas and the spatial distribution of the composite observing system and to the different atmospheric predictability in these two periods.

An exhaustive validation of operational ocean forecast products available in the Gibraltar Strait and the Alboran Sea is presented. The skill of two ocean model solutions (i.e. the regional CMEMS IBI and the local PdE SAMPA ones) in reproducing the complex surface dynamics in the above areas is evaluated. To this aim, in-situ measurements from 35 drifter buoys (the MEDESS-GIB database) are used as observational reference. A Lagrangian separation distance and a skill score have been applied to evaluate the performance of the modeling systems in reproducing the observed trajectories. Furthermore, the SST validation with in-situ data is carried out by means of validating the model solutions with L3 satellite SST products. The IBI products are evaluated in an extended domain, beyond the Alboran Sea, covering western Mediterranean waters. This analysis reveals some strengths of the regional solution (i.e. realistic values of the Atlantic Jet in the Strait, realistic simulation of the Algerian Current), together with some shortcomings (the major one related to the simulated geographical position and intensity of the Alboran Gyres, particularly the western one). On the other hand, the SAMPA system shows a more accurate model performance and it realistically reproduces the observed surface circulation in the area. The results reflect the effectiveness of the dynamical downscaling performed through the SAMPA system with respect to the regional IBI solution (in which SAMPA is nested), providing an objective measure of the potential added values introduced by the SAMPA downscaling solution in the Alboran Sea.

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 largescale 'father' system in future downscaling approaches by providing coherent open boundary conditions to nested high-resolution coastal models.

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