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The Mediterranean Sea is a prominent climate-change hot spot, with many socioeconomically vital coastal areas being the most vulnerable targets for maritime safety, diverse met-ocean hazards and marine pollution. Providing an unprecedented spatial and temporal resolution at wide coastal areas, high-frequency radars (HFRs) have been steadily gaining recognition as an effective land-based remote sensing technology for continuous monitoring of the surface circulation, increasingly waves and occasionally winds. HFR measurements have boosted the thorough scientific knowledge of coastal processes, also fostering a broad range of applications, which has promoted their integration in coastal ocean observing systems worldwide, with more than half of the European sites located in the Mediterranean coastal areas. In this work, we present a review of existing HFR data multidisciplinary science-based applications in the Mediterranean Sea, primarily focused on meeting end-user and science-driven requirements, addressing regional challenges in three main topics: (i) maritime safety, (ii) extreme hazards and (iii) environmental transport process. Additionally, the HFR observing and monitoring regional capabilities in the Mediterranean coastal areas required to underpin the underlying science and the further development of applications are also analyzed. The outcome of this assessment has allowed us to provide a set of recommendations for future improvement prospects to maximize the contribution to extending science-based HFR products into societally relevant downstream services to support blue growth in the Mediterranean coastal areas, helping to meet the UN's Decade of Ocean Science for Sustainable Development and the EU's Green Deal goals., peer-reviewed

Due to the semi-enclosed nature of the Mediterranean Sea, natural disasters and anthropogenic activities impose stronger pressures on its coastal ecosystems than in any other sea of the world. With the aim of responding adequately to science priorities and societal challenges, littoral waters must be effectively monitored with high-frequency radar (HFR) systems. This land-based remote sensing technology can provide, in near-real time, fine-resolution maps of the surface circulation over broad coastal areas, along with reliable directional wave and wind information. The main goal of this work is to showcase the current status of the Mediterranean HFR network and the future roadmap for orchestrated actions. Ongoing collaborative efforts and recent progress of this regional alliance are not only described but also connected with other European initiatives and global frameworks, highlighting the advantages of this cost-effective instrument for the multi-parameter monitoring of the sea state. Coordinated endeavors between HFR operators from different multi-disciplinary institutions are mandatory to reach a mature stage at both national and regional levels, striving to do the following: (i) harmonize deployment and maintenance practices; (ii) standardize data, metadata, and quality control procedures; (iii) centralize data management, visualization, and access platforms; and (iv) develop practical applications of societal benefit that can be used for strategic planning and informed decision-making in the Mediterranean marine environment. Such fit-for-purpose applications can serve for search and rescue operations, safe vessel navigation, tracking of marine pollutants, the monitoring of extreme events, the investigation of transport processes, and the connectivity between offshore waters and coastal ecosystems. Finally, future prospects within the Mediterranean framework are discussed along with a wealth of socioeconomic, technical, and scientific challenges to be faced during the implementation of this integrated HFR regional network., This study has been partially developed in the framework of the Interreg MED Strategic Project SHAREMED, co-financed by the European Regional Development Fund under the funding program Interreg MED 2014–2020. Website: https://sharemed.interreg-med.eu/ (last access: 31 March 2022). We are also grateful for the partial support of the (i) the project PO FEAMP 2014/2020 (Misura 2.51) funded by Regione Campania (Italy), (ii) the 2017 PRIN project EMME (Exploring the fate of Mediterranean microplastic: from distribution pathways to biological effects) funded by the Italian Ministry for Research (grant agreement no. 2017WERYZP), and (iii) the CMEMS-INSTAC phase II, which provides the context of the activities for HFR data harmonization, standardization, and distribution. Collaborative discussion on data management harmonization at the European level has also been carried out thanks to the contribution of the projects INCREASE (CMEMS Service Evolution Call for Tenders 21-SE-CALL1) and SeaDataCloud (EU-H2020 GA no. 730960).

The Mediterranean Sea is a prominent climate change hot spot, being their socio-economically vital coastal areas the most vulnerable targets for maritime safety, diverse met-ocean hazards and marine pollution. Providing an unprecedented spatial and temporal resolution at wide coastal areas, High-frequency radars (HFRs) have been steadily gaining recognition as an effective land-based remote sensing technology for a continuous monitoring of the surface circulation, increasingly waves and occasionally winds. HFR measurements have boosted the thorough scientific knowledge of coastal processes, also fostering a broad range of applications, which has promoted their integration in the Coastal Ocean Observing Systems worldwide, with more than half of the European sites located in the Mediterranean coastal areas. In this work, we present a review of existing HFR data multidisciplinary science-based applications in the Mediterranean Sea, primarily focused on meeting end-users and science-driven requirements, addressing regional challenges in three main topics: i) maritime safety; ii) extreme hazards; iii) environmental transport process. Additionally, the HFR observing and monitoring regional capabilities in the Mediterranean region required to underpin the underlying science and the further development of applications are also analyzed. The outcome of this assessment has allowed us to finally provide a set of recommendations for the future improvement prospects to maximize the contribution in extending the science-based HFR products into societal relevant downstream services to support the blue growth in the Mediterranean coastal areas, helping to meet the UN’s Decade of Ocean Science for Sustainable Development and the EU’s Green Deal goals.

Due to the semi-enclosed nature of the Mediterranean Sea, natural disasters and anthropogenic activities impose stronger pressures on its coastal ecosystems than in any other sea of the world. With the aim of responding adequately to science priorities and societal challenges, littoral waters must be effectively monitored with High-Frequency radar (HFR) systems. This land-based remote sensing technology can provide, in near real-time, fine-resolution maps of the surface circulation over broad coastal areas, along with reliable directional wave and wind information. The main goal of this work is to showcase the current status of the Mediterranean HFR network and the future roadmap for orchestrated actions. Ongoing collaborative efforts and recent progress of this regional alliance are not only described but also connected with other European initiatives and global frameworks, highlighting the advantages of this cost-effective instrument for the multi-parameter monitoring of the sea state. Coordinated endeavours between HFR operators from different multi-disciplinary institutions are mandatory to reach a mature stage at both national and regional levels, striving to: i) harmonize deployment and maintenance practices; ii) standardize data, metadata and quality control procedures; iii) centralize data management, visualization and access platforms; iv) develop practical applications of societal benefit, that can be used for strategic planning and informed decision-making in the Mediterranean marine environment. Such fit-for-purpose applications can serve for search and rescue operations, safe vessel navigation, tracking of marine pollutants, the monitoring of extreme events or the investigation of transport processes and the connectivity between offshore waters and coastal ecosystems. Finally, future prospects within the Mediterranean framework are discussed along with a wealth of socio-economic, technical and scientific challenges to be faced during the implementation of this integrated HFR regional network.

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.

This report describes the governance of the European HF radar network including: the landscape of the Ocean observation networks and infrastructures, the role and links between operators of observational systems and stakeholders, the role and activities of the EuroGOOS HF radar Task Team in building a sound community strategy, the roadmap of the community with current achievements and future work lines.

35 pages, 12 figures, 7 tables.-- Data Availability Statement: The following publicly available datasets were analyzed in this study: Model data: The CMEMS IBI MFC operational forecast product can be found in the CMEMS catalogue (IBI-MFC forecast analysis product: https://resources.marine.copernicus.eu/?option=com_csw&view=details&product_id=IBI_ANALYSISFORECAST_PHY_005_001 (accessed on 8 April 2021)); LAMBDA river data can be found in: http://www.cmems-lambda.eu/#data-portal (accessed on 8 April 2021); data from the different ocean model scenarios analyzed in the study can be available on request from the corresponding author. Observational data: The data from in-situ buoys, Argo floats and Recopesca can be found in the CMEMS catalogue (Insitu-TAC Near-Real-Time observational product: https://resources.marine.copernicus.eu/?option=com_csw&view=details&product_id=INSITU_IBI_NRT_OBSERVATIONS_013_033 (accessed on 8 April 2021)). The salinity data from SMOS (the low-resolution level 3 SSS product computed with smoothening spatial window of 50-km radius) can be found in the BEC public ftp catalogue: http://bec.icm.csic.es/bec-ftp-service/ (accessed on 8 April 2021); Finally, the INTECMAR and IPMA observational salinity datasets used in this study are 3rd Party Data, and restrictions are applied to their availability (contact with the institutions owner of these datasets would be required for access permission), River freshwater contribution in the European Atlantic margin and its influence on the sea salinity field are analyzed. The impacts of using a new river discharge database as part of the freshwater forcing in a regional ocean model are assessed. Ocean model scenarios, based on the CMEMS (Copernicus Marine Environment Monitoring Service) operational IBI-MFC (Iberia Biscay Ireland Monitoring Forecasting Centre) model set-up, are run to test different (observed, modeled and climatological) river and coastal freshwater forcing configurations throughout 2018. The modelled salinity fields are validated, using as a reference all known available in-situ observational data sources. The IBI model application is proven to adequately simulate the regional salinity, and the scenarios showcase the effects of varying imposed river outflows. Some model improvement is achieved using the new forcing (i.e., better capture of salinity variability and more realistic simulation of baroclinic frontal structures linked to coastal and river freshwater buoyancy plumes). Major impacts are identified in areas with bigger river discharges (i.e., the French shelf or the northwestern Iberian coast). Instead, the Portuguese shelf or the Gulf of Cadiz are less impacted by changes in the imposed river inflows, and other dynamical factors in these areas play a major role in the configuration of the regional salinity, Part of this research work was conducted in the framework of the following 2 projects: The EU Interreg Atlantic Area MyCoast Project EAPA_285/2016 (F.C., A.M. and M.G.S.) and the CMEMS Service Evolution Project LAMBDA (F.C., F.S., E.O. and A.N.). It was also supported by activity from the CMEMS IBI-MFC (K.G., P.L. and A.A.B.), With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

The Mediterranean Sea is considered a relevant geostrategic region and a prominent climate change hot spot. This semi-enclosed basin has been the subject of abundant studies due to its vulnerability to sea-level rise and other coastal hazards. With the steady advent of new technologies, a growing wealth of observational data are nowadays available to efficiently monitor the sea state and properly respond to socio-ecological challenges and stakeholder needs, thereby strengthening the community resilience at multiple scales.Nowadays, High-Frequency radar (HFR) is a worldwide consolidated land-based remote sensing technology since it provides, concurrently and in near real time, fine-resolution maps of the surface circulation along with (increasingly) wave and wind information over broad coastal areas. HFR systems present a wide range of practical applications: maritime safety, oil spill emergencies, energy production, management of extreme coastal hazards. Consequently, they have become an essential component of coastal ocean observatories since they offer a unique dynamical framework that complement conventional in-situ observing platforms. Likewise, within the frame of the Copernicus Marine Environment Monitoring Service (CMEMS), HFR are valuable assets that play a key pivotal role in both the effective monitoring of coastal areas and the rigorous skill assessment of operational ocean forecasting systems.The present work aims to show a panoramic overview not only of the current status of diverse Mediterranean HFR systems, but also of the coordinated joint efforts between many multi-disciplinary institutions to establish a permanent HFR monitoring network in the Mediterranean, aligned with European and global initiatives. In this context, it is worth highlighting that many of the Mediterranean HFR systems are already integrated into the European HFR Node, which acts as central focal point for data collection, homogenization, quality assurance and dissemination and promotes networking between EU infrastructures and the Global HFR network.Furthermore, priority challenges tied to the implementation of a long-term, fully integrated, sustainable operational Mediterranean HFR network are described. This includes aspects related to the setting up of such a system within the broader framework of the European Ocean Observing System (EOOS), and a long-term financial support required to preserve the infrastructure core service already implemented. Apart from the technological challenges, the enhancing of the HFR data discovery and access, the boosting of the data usage as well as the research integration must be achieved by building synergies among academia, management agencies, state government offices, intermediate and end users. This would guarantee a coordinated development of tailored products that meet the societal needs and foster user uptake, serving the marine industry with dedicated smart innovative services, along with the promotion of strategic planning and informed decision-making in the marine environment.

On January 19th-24th 2020, the Western Spanish Mediterranean (WM) coast was hit by the storm Gloria, one of the most extreme meteorological events ever recorded in the region. A strong North-South atmospheric pressure gradient, linked to a high atmospheric pressure system centred over the British Islands (1050hPa), favoured outstanding easterly winds across the WM. Several buoys moored along the Iberian Mediterranean coast beat their record of significant wave height (reaching 8.44 m at Valencia buoy) and a wind-driven storm-surge locally beat the record along the Valencia coastline.Operational storm-surge forecasts were provided by different services at the WM area. Models presented both commonalities and differences, due to their intrinsic features (physics, resolution, forcing data, assimilation scheme, etc). A way to synthetise all these model outcomes, is by building an ensemble that integrates all of them. Ensemble techniques, such as Bayesian Model Average (BMA), not only generate combined forecasts; but also may compute confidence intervals, that are specially suitable when the ensemble members diverge.Since 2018, the Puertos del Estado (PdE) ENSURF (ENsemble SURge Forecast) system delivers probabilistic forecasts at WM tidal stations, by combining in a BMA: (i) near-real time tide gauge data and (ii) forecasts from the PdE Nivmar system and the CMEMS MED-MFC and IBI-MFC services. Consequently, this contribution aims to assess the performance of these storm-surge forecasts under storm Gloria at two levels: (i) individually and (ii) integrated within the ENSURF system. Each forecast solution has been analysed at several tidal stations, and no single model outperforms at all tidal stations and synoptic conditions. Then, it is confirmed that the probabilistic forecast gives significant added value with respect to existing operational systems.At an individual level, on those tidal stations in which the surge was mainly wave and wind-driven, MED-MFC performed better, with emphasis on the growth-phase of the surge. IBI-MFC showed good skill on those stations with wind-driven surges, and those mean sea level pressure-driven (MLSP) surges in which the Atlantic-Med water-mass exchanges are important. Finally, Nivmar exhibited good performance on MSLP-driven surges.At the integrated level, the ENSURF forecast presents lower bias and RMS, plus higher correlation than most of its ensemble members. Despite these error metrics, though, further work is also needed on the BMA for estimating the peak of the storm-surge event. The results for this contribution, then, may serve to plan forthcoming improvements in the current coastal sea-level forecast systems.

Upwelling and downwelling processes play a critical role in the connectivity between offshore waters and coastal ecosystems, having relevant implications in terms of intense biogeochemical activity and global fisheries production. A variety of in situ and remote-sensing networks were used in concert with the Iberia&ndash, Biscay&ndash, Ireland (IBI) circulation forecast system, in order to investigate two persistent upwelling and downwelling events that occurred in the Northwestern (NW) Iberian coastal system during summer 2014. Special emphasis was placed on quality-controlled surface currents provided by a high-frequency radar (HFR), since this land-based technology can effectively monitor the upper layer flow over broad coastal areas in near-real time. The low-frequency spatiotemporal response of the ocean was explored in terms of wind-induced currents&rsquo, structures and immediacy of reaction. Mean kinetic energy, divergence and vorticity maps were also calculated for upwelling and downwelling favorable events, in order to verify HFR and IBI capabilities, to accurately resolve the prevailing surface circulation features, such as the locus of a persistent upwelling maximum in the vicinity of Cape Finisterre. This integrated approach proved to be well-founded to efficiently portray the three-dimensional characteristics of the NW Iberian coastal upwelling system regardless of few shortcomings detected in IBI performance, such as the misrepresentation of the most energetic surface dynamics or the overestimation of the cooling and warming associated with upwelling and downwelling conditions, respectively. Finally, the variability of the NW Iberian upwelling system was characterized by means of the development of a novel ocean-based coastal upwelling index (UI), constructed from HFR-derived hourly surface current observations (UIHFR). The proposed UIHFR was validated against two traditional UIs for 2014, to assess its credibility. Results suggest that UIHFR was able to adequately categorize and characterize a wealth of summer upwelling and downwelling events of diverse length and strength, paving the way for future investigations of the subsequent biophysical implications.

One of the challenges of the Iberia-Biscay-Ireland (IBI) Monitoring Forecasting Centre in CMEMS phase 2 is the implementation of the assimilation of altimeter wave data in the wave forecast system. In this work we explored the impact of the assimilation of altimeter wave data in the IBI domain. We ran the Météo France version of the WAM wave model (MFWAM) in the IBI domain for 2018 and 2019, with data assimilated from the Jason 2 and 3, Saral, Cryosat 2 and Sentinel 3 altimeters. This high-resolution (0.05 degree) configuration was forced by 0.05 degree ECMWF winds, and boundary conditions were provided by a 0.1 degree global model run. We also included refraction from currents generated with the NEMO-IBI ocean circulation model. We present results with and without wave–current interactions. Validation against both buoy data and the HaiYang 2 altimeter shows that the assimilation of data leads to a marked reduction in scatter index and model bias compared to the run without data assimilation; the gains from including currents meanwhile are modest. The data assimilation scheme presently implemented in MFWAM uses an optimal interpolation algorithm where constant model and observational errors are assumed. To add some sophistication, we experimented with non-constant background errors derived from a model ensemble. Though the effect was small, the method suggests a way to improve the data assimilation performance without substantially altering the algorithm.

High-frequency (HF) radars are efficient tools for measuring vast areas and gathering ocean parameters in real-time. However, the accuracy of their wave estimates is under analysis. This paper presents a new methodology for analyzing and validating the wave data estimated by two CODAR SeaSonde radars located on the Galician coast (NW Spain). Approximately one and a half years of wave data (January, 2014–April, 2015) were obtained for ten range cells employing two different sampling times used by the radar software. The resulting data were screened by an updated method, and their abundance and quality were described for each radar range cell and different wave regime; the latter were defined using the spectral significant wave height (Hm0) and mean wave direction (Dm) estimated by two buoys and three SIMAR points (SImulación MARina in Spanish, from the wave reanalysis model by Puertos del Estado (PdE)). The correlation between the results and the particularities of the different sea states (broadband or bimodal), the wind and the operation of the devices are discussed. Most HF radar wave parameters’ errors occur for waves from the NNE and higher than 6 m. The best agreement between the Vilán radar and the Vilano-Sisargas buoy wave data was obtained for the dominant wave regime (from the northwest) and the southwest wave regime. However, relevant contradictions regarding wave direction were detected. The possibilities of reducing the wave parameters’ processing time by one hour and increasing the numbers of range cells of the radars have been validated This research was funded by Interreg Atlantic Area project MyCOAST (EAPA 285/2016) and INTERREG V-A Spain-Portugal (POCTEP) project RADAR_ON_RAIA co-funded by the European Regional Development Fund (ERDF) (EU). V.P.-M. and A.B. acknowledge financial support by CRETUS strategic partnership (ED431E2018/01), co-funded by the ERDF (EU) http://www.usc.es/cretus/ SI

SAMOA (Sistema de Apoyo Meteorológico y Oceanográfico de la Autoridad Portuaria) is the latest initiative of Puertos del Estado, the Spanish Public State Port Agency, to enhance the delivery of user-customised operational met-ocean information to aid Spanish Port Authorities making harbour safety, environmental management and operational decisions. This initiative provides high-resolution coastal operational prediction systems in domains such as harbours and nearby coastal waters. Forecast systems implemented are fully operational from January 2017 for nine Spanish ports in the Mediterranean, the Iberian Atlantic and the Canary Islands. This paper provides an end-to-end description of these SAMOA systems that are based on high-resolution ROMS model applications. The SAMOA systems are CMEMS downstream services, being the coastal models nested into the regional IBI forecast solution. At the surface, SAMOA systems use as forcing daily updated hourly winds and heat and water fluxes from the Spanish Meteorological Agency forecast services. Highlights from the scientific pre-operational model evaluation phase and the multi-parametric validation are shown, illustrating agreements between SAMOA products and in-situ and remoted sensed observations. To this aim, skill metrics (such as bias, errors, Taylor diagrams and correlations) are presented. Finally, a look ahead to future SAMOA developments and operational innovations is provided.

Editors: Karina von Schuckmann; Pierre-Yves Le Traon.-- Review Editors: Neville Smith (Chair); Ananda Pascual; Samuel Djavidnia; Jean-Pierre Gattuso; Marilaure Grégoire; Glenn Nolan., The authors would like to thank the Institut Cartogràfic i Geològic de Catalunya (ICGC) for providing data. Thanks are due to FCT/MCTES for the financial support to CESAM (UID/AMB/50017/2019), through national funds., Chapter 1: Introduction and the European Environment policy framework.-- CMEMS OSR4, Chapter 2: State, variability and change in the ocean.-- CMEMS OSR4, Chapter 3: Case studies.-- CMEMS OSR4, Chapter 4: Specific events 2018.

This paper describes a case of the implementation of a pan-European operational oceanography service coexisting with non-operative research jobs that are executed on the same computational resources. The complexity of designing a good operational service increases when the resources that will be used are shared with other computational workloads. However, once the implementation is achieved the result is an optimised and robust service. Computational resources and other necessary services are permanently monitored in order to detect and solve potential problems in real-time. These resources can be used by other researchers during the time interval in which they are not needed for this operational service. The goal of this work is to guarantee the time to solution of the operational execution on a shared computing environment without a large impact on the researchers jobs.

The fundamental role of the ocean for life and well-being on Earth is more and more recognised at the highest political level. In 2015, the United Nations (UN) Sustainable Development Goals (SDGs) of the 2030 Agenda for Sustainable Development were adopted by world leaders. The SDG 14 ‘Conserve and sustainably use the oceans, seas and marine resources for sustainable development’ is dedicated to the oceans. The mention of the ocean in the Paris Agreement signed in 2016 marked a decisive milestone. In 2018, the UN Decade of Ocean Science for Sustainable Development (2021–2030) has been proclaimed (https://en.unesco.org/ocean-decade): The Intergovernmental Oceanographic Commission of UNESCO will gather ocean stakeholders worldwide behind a common framework to foster evidence-based policy-making. In fall 2019, the IPCC special report on ocean and cryosphere will be published, and will provide an opportunity to increase awareness and action before COP251 (already claimed as ‘Blue COP’).

Operational oceanography can be described as the provision of routine oceanographic information needed for decision-making purposes. It is dependent upon sustained research and development through the end-to-end framework of an operational service, from observation collection to delivery mechanisms. The core components of operational oceanographic systems are a multi-platform observation network, a data management system, a data assimilative prediction system, and a dissemination/accessibility system. These are interdependent, necessitating communication and exchange between them, and together provide the mechanism through which a clear picture of ocean conditions, in the past, present, and future, can be seen. Ocean observations play a critical role in all aspects of operational oceanography, not only for assimilation but as part of the research cycle, and for verification and validation of products. Data assimilative prediction systems are advancing at a fast pace, in tandem with improved science and the growth in computing power. To make best use of the system capability these advances would be matched by equivalent advances in operational observation coverage. This synergy between the prediction and observation systems underpins the quality of products available to stakeholders, and justifies the need for sustained ocean observations. In this white paper, the components of an operational oceanographic system are described, highlighting the critical role of ocean observations, and how the operational systems will evolve over the next decade to improve the characterization of ocean conditions, including at finer spatial and temporal scales.

Academic, government, and private organizations from around the globe have established High Frequency radar (hereinafter, HFR) networks at regional or national levels. Partnerships have been established to coordinate and collaborate on a single global HFR network (http://global-hfradar.org/ ). These partnerships were established in 2012 as part of the Group on Earth Observations (GEO) to promote HFR technology and increase data sharing among operators and users. The main product of HFR networks are continuous maps of ocean surface currents within 200 km of the coast at high spatial (1-6 km) and temporal resolution (hourly or higher). Cutting-edge remote sensing technologies are becoming a standard component for ocean observing systems, contributing to the paradigm shift towards ocean monitoring. In 2017 the Global HFR Network was recognized by the Joint Technical WMO-IOC Commission for Oceanography and Marine Meteorology (JCOMM) as an observing network of the Global Ocean Observing System (GOOS). In this paper we will discuss the development of the network as well as establishing goals for the future. The U.S. High Frequency Radar Network (HFRNet) has been in operation for over thirteen years, with radar data being ingested from 31 organizations including measurements from Canada and Mexico. HFRNet currently holds a collection from over 150 radar installations totaling millions of records of surface ocean velocity measurements. During the past 10 years in Europe, HFR networks have been showing steady growth with over 60 stations currently deployed and many in the planning stage. In Asia and Oceania countries, more than 110 radar stations are in operation. HFR technology can be found in a wide range of applications: for marine safety, oil spill response, tsunami warning, pollution assessment, coastal zone management, tracking environmental change, numerical model simulation of 3-dimensional circulation, and research to generate new understanding of coastal ocean dynamics, depending mainly on each country's coastal sea characteristics. These radar networks are examples of national inter-agency and inter-institutional partnerships for improving oceanographic research and operations. As global partnerships grow, these collaborations and improved data sharing enhances our ability to respond to regional, national, and global environmental and management issues.

The Iberian Biscay Ireland (IBI) wave system has the challenge to improve wave forecast and the coupling with ocean circulation model dedicated to western european coast. The momentum and heat fluxes at the sea surface are strongly controlled by the waves and there is a need of using accurate sea state from wave model. This work describes the more recent version of the IBI wave system and highlight the performance of system in comparison with satellite altimeters and buoys wave data. The validation process has been performed for 1-year run of the wave model MFWAM with boundary conditions provided by the global wave system. The results show on the one hand a slightly improvement on significant wave height and peak period, and on the other hand a better surface stress for high wind conditions. This latter is a consequence of using a tail wave spectrum shaped as the Philipps wave spectrum for high frequency waves.

This work aims to evaluate the ocean/waves coupling based on input from the wave modelMFWAM. 1-year coupled runs including seasonal variability has been performed for the IberianBiscay and Ireland domain. We investigated the consequences of improvement in wave physics onthe mixed layer of the ocean with a fine horizontal grid size of 1/36°. The ocean model NEMO andthe wave model MFWAM have been used for this study to prepare the use of coupling operationallyin the IBI Copernicus Marine Service and Monitoring Evironment (CMEMS). Two wave physicsversions have been discussed in this study. The validation of sea surface temperature, surfacecurrents have been implemented in comparison with satellite and in-situ observations. The resultsshow a positive impact of the waves forcing on surface key parameters. For storm cases it has beendemonstrated a good skill of the ocean/wave coupling to capture the peak of surge event such as theone observed for Petra storm.

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 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 data assimilation in open-waters and the increased horizontal resolution of IBI in coastal areas, respectively. Besides, IBI 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 the nested SAMPA high-resolution coastal forecast system in order to elucidate the accuracy of each system to characterize the Atlantic Jet (AJ) inflow dynamic. A quantitative validation against High Frequency radar (HFR) hourly currents highlighted both the steady improvement in AJ representation in terms of speed and direction when zooming from global to coastal scales though 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-day 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 potential added value of coastal models with respect to coarser parent regional 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.

The present work focuses on the long-term coastal monitoring of the Atlantic surface inflow into the Mediterranean basin through the Strait of Gibraltar. Hourly current maps provided during 2016&ndash, 2017 by a High Frequency radar (HFR) system were used to characterize the Atlantic Jet (AJ) since changes in its speed and direction modulate the upper-layer circulation of the Western Alboran Gyre (WAG). The AJ pattern was observed to follow a marked seasonal cycle. A stronger AJ flowed north-eastwards during autumn and winter, while a weaker AJ was directed more southwardly during the middle of the year, reaching a minimum of intensity during summertime. A strong relationship between AJ speeds and angles was evidenced: the AJ appeared to be frequently locked at an angle around 63&deg, measured clockwise from the North. The AJ speed usually fluctuated between 50 cm&middot, s&minus, 1 and 170 cm&middot, 1, with occasional drops below 50 cm&middot, 1 which were coincident with abrupt modifications in AJ orientation. Peaks of current speed clearly reached values up to 250 cm&middot, 1, regardless of the season. A number of persistent full reversal episodes of the surface inflow were analyzed in terms of triggering synoptic conditions and the related wind-driven circulation patterns. High sea level pressures and intense (above 10 m&middot, 1), permanent and spatially-uniform easterlies prevailed over the study domain during the AJ collapse events analyzed. By contrast, tides seemed to play a secondary role by partially speeding up or slowing down the westward currents, depending on the phase of the tide. A detailed characterization of this unusual phenomenon in the Strait of Gibraltar is relevant from diverse aspects, encompassing search and rescue operations, the management of accidental marine pollution episodes or efficient ship routing.