The present study aims to estimate effective diahaline turbulent salinity fluxes and diffusivities in numerical model simulations of estuarine scenarios. The underlying method is based on a quantification of salinity mixing per salinity class, which is shown to be twice the turbulent salinity transport across the respective isohaline. Using this relation, the recently derived universal law of estuarine mixing, predicting that average mixing per salinity class is twice the respective salinity times the river run‐off, can be directly derived. The turbulent salinity transport is accurately decomposed into physical (due to the turbulence closure) and numerical (due to truncation errors of the salinity advection scheme) contributions. The effective diahaline diffusivity representative for a salinity class and an estuarine region results as the ratio of the diahaline turbulent salinity transport and the respective (negative) salinity gradient, both integrated over the isohaline area in that region and averaged over a specified period. With this approach, the physical (or numerical) diffusivities are calculated as half of the product of physical (or numerical) mixing and the isohaline volume, divided by the square of the isohaline area. The method for accurately calculating physical and numerical diahaline diffusivities is tested and demonstrated for a three‐dimensional idealized exponential estuary. As a major product of this study, maps of the spatial distribution of the effective diahaline diffusivities are shown for the model estuary.

How to cite: Burchard, H., Gräwe, U., Klingbeil, K., Koganti, N., Lange, X., and Lorenz, M.: Effective Diahaline Diffusivities in Estuaries, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7712, https://doi.org/10.5194/egusphere-egu21-7712, 2021.

Estuaries and coastal bays are areas of large spatial-temporal variability in physical and biological variables due to environmental factors such as local wind, light availability, freshwater inputs or tides. The physical characteristics of an estuary affect its hydrodynamics. These in turn modify the behaviour of biological variables such as the concentration of chlorophyll a (Chl a). In a small-scale, micro tidal bay such as the Fangar Bay (Ebro Delta), hydrodynamics is influenced above all by local winds, as well as by fresh water contributions. The results of two field campaigns and Sentinel-2 images show how the concentration of Chl a is affected by strong wind episodes typical of this area (NW-E winds). With these episodes of strong wind (> 10 m-s-1) mixing occurs in the water column causing an increase in the concentration of Chl a. On the other hand, with sea breezes (< 6 m-s-1) the water column is stratified causing a decrease in the Chl a concentration. However, the spatial-temporal variability of Chl a in small-scale estuaries and coastal bays is quite complex due to the many factors involved and deserves more intensive field campaigns and additional numerical modelling efforts.

How to cite: F-Pedrera Balsells, M., Grifoll, M., Fernández-Tejedor, M., Espino, M., and Sánchez-Arcilla, A.: Influence of the hydrodynamics in spatio-temporal variability of clorophyll a in a small-scale and microtidal bay: Fangar Bay case (Ebro Delta), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7568, https://doi.org/10.5194/egusphere-egu21-7568, 2021.

Direct estimate of ocean surface motion sensed by the Doppler shift of the surface includes ocean surface current and a wind-wave induced artefact surface velocity (WASV). The Sentinel-1 (S1) C-band SAR mission includes direct ocean surface motion estimates as an operational Level-2 Ocean (OCN) Radial VeLocity (RVL) product. The existing operational RVL products suffer from significant uncorrected platform and instrument effects that presently prevent exploitation of the data. This paper proposes a simple method to calibrate and correct for these effects and evaluate the benefit of these corrections over 2.5 years S1A acquisition against ground truth measurements. A specific geometry for S1 has been chosen for S1-A over the HF radar (HFR) instrumented site in the German Bight. The 78 S1A snapshots end in 56 match-ups within 20 minutes of HFR measurements. HFR velocity fields were projected in the same radial direction as S1A. Land calibration corrects for constant snapshot biases of the operational products up to 2 m/s. Besides these constant biases there is persistent relative biases within snapshots between up to 0.4 m/s in addition to the TOPSAR uncorrected scalloping effect with an amplitude of 0.1 m/s. After calibration, corrected RVL are compared against HFR with various WASV correction. Applying WASV correction with a reduced 70% C-Dop model, gives the best results with a precision of 0.25 m/s and correlation in time of 0.9. This might be due to C-Dop amplitude in up/downwind being too strong for a coastal environment as encountered in the German Bight. Quadratic mean of all 78 S1A snapshots after all corrections applied exhibits coastal current jets in good agreement with bathymetry channels and is promising as a cheap way to infer local bathymetry channels.

How to cite: Gommenginger, C., Martin, A. C. H., Jacob, B., and Staneva, J.: Multi-year assessment of ocean surface currents from Copernicus Sentinel-1 and HF radar in the German Bight, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15280, https://doi.org/10.5194/egusphere-egu21-15280, 2021.

The UK coast is under  increasing risk due to coastal change, cliffs are collapsing endangering houses near the coast and of the 12,400 km of  coastline, 2,500 km present a flooding risk. Constant monitoring is necessary in order to keep coastal evolution under surveillance and to adapt the measures to mitigate the impact of coastal change. Earth Observation technology is unique in that it has now been available for over 25 years and currently there is a range of satellites both civil and commercial that are constantly viewing our coast. Satellite imagery provides large scale observation at a high spatial resolution with an average revisit time of 5 days for most missions. Temporal and spatial resolution are key components to provide a continuous monitoring service of a coast. Using the balance of ever increasing resolution coupled to a range of innovative techniques that make full use of the spectral signatures being captured enables us to recreate the coastal boundary to a high degree of reliability over complete national coastlines.

Our developed methodology combines different types of products to completely characterize the different coastal environments. The land/sea boundary is used to monitor changes along the coast and combine with a backshore land use, land cover classification map, we are able to bring contextual information on coastal vulnerability and their erosive potential. Our LiuJezek_CoastL processor extracts the instantaneous land/sea boundary from all satellite observations available and provides a vector line which represents the coast morphology depending on sea level at the time of the acquisition. This line is then corrected from all water dynamics such as waves, tidal level to create shorelines at a reference datum height. The error in positioning the shoreline is relaint on beach slopes, for example in the case of cliffs or civil works along the coast compared to long shelfing beaches. Our backshore classification, provides land use and land cover information which can correct the shoreline position according to the features present along the coast.

How to cite: Jones, M. and Payo. Garcia, A.: Continuous surveillance of UK coastline using EO data to monitor coastal change impact, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16013, https://doi.org/10.5194/egusphere-egu21-16013, 2021.

The Angola-Benguela frontal region represents an extremely dynamic portion of the ocean located along the south-western African coast, at the northern edge of the South Atlantic gyre. At this boundary, the northern warm and saline waters of the Angola Basin mix with the southern colder and fresher waters carried by the Benguela current through a combination of processes that span a wide range of spatio-temporal scales. This study combines the use of underwater glider data collected between February and June 2018 with a high resolution 3D physical-biogeochemical model to investigate how these lateral exchanges impact the oxygen and organic carbon distributions in the proximity of the front. From the glider data, we identify a set of salinity, oxygen and organic carbon anomalies impacting the first 500 m of the water column during February-June 2018. Using satellite images of physical and biological data and an eddy identification algorithm, we discuss these anomalies in the context of the surrounding physical and biological setting at the time of measurement and identify key processes that may be responsible for the observed tracer patterns. We employ the Regional Ocean Modeling System (ROMS) coupled with the Biogeochemistry Ecosystem Circulation model (BEC) to further explain and upscale our findings. We study the dynamics of cross-frontal exchanges of oxygen and organic carbon in the first 500 m depth. We show how the coupling between long filaments and intense anticyclonic eddies forming at the front generates a complex pattern of recirculation of Angola Basin-derived saline and low-oxygen waters into the oxygenated Benguela region. Finally, we quantify the oxygen lateral transport coupled with these dynamics, and discuss the implications for the biological activity in the region.

How to cite: Lovecchio, E., Henson, S., Carvalho, F., and Briggs, N.: Combining gliders and models to understand mesoscale biogeochemical patterns at the Angola-Benguela front, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8494, https://doi.org/10.5194/egusphere-egu21-8494, 2021.

Climate-related sea level changes in the world coastal zones result from the superposition of the global mean rise due to ocean warming and land ice melt, regional changes mostly caused by non-uniform ocean thermal expansion and salinity changes, and small-scale coastal processes (e.g., shelf currents, wind & waves changes, fresh water input from rivers, etc.). So far, satellite altimetry has provided global gridded sea level time series up to 10-15 km to the coast only, preventing estimation of sea level changes very close to the coast. In the context of the ESA Climate Change Initiative coastal sea level project, we have developed a complete reprocessing of high-resolution (20 Hz) Jason-1, 2 and 3 altimetry data along the world coastal zones using the ALES (Adaptative Leading Edge Subwaveform) retracker combined with the XTRACK system dedicated to improve geophysical corrections at the coast. Here we present coastal sea level trends over the period 2002-2020 along the whole African continent. Different coastal sea level trend behaviors are observed over the study period. We compare the computed coastal trends in Africa with results we previously obtained in other regions (Mediterranean Sea, Northeastern Europe, north Indian Sea, southeast Asia and Australia).

How to cite: Gouzenes, Y., Cazenave, A., Léger, F., Birol, F., Passaro, M., Nino, F., Calafat, F., Shaw, A., Legeais, J.-F., and Benveniste, J.: Coastal sea level changes in Africa from retracked Jason altimetry over 2002-2020, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14643, https://doi.org/10.5194/egusphere-egu21-14643, 2021.

This paper analyses the summer water circulation in Barcelona, Tarragona and Castellón harbours (east and north-east of Spain), based on field data acquired between April and September 2019. These data include information of wind, waves, 1DV currents, temperature and salinity parameters. The research characterizes the hydrodynamics at the mouth of each harbour and allows to estimate circulation patterns according to its physical characteristics. The availability of simultaneous data on the three harbours allows to analyse and study possible differences. The results show a two-layer circulation in all the harbours. In the cases of Tarragona and Castellón, both with a single mouth, the surface layer flows out of the harbour and the bottom currents circulate inwards. This pattern is reversed in the Barcelona harbour, which has two mouths and is more influenced by the local winds, affecting the distribution of currents in the water column. The bottom water temperature reveals significative differences between the three harbours, especially during the first half of the summer. The results suggest that sea level effects and the water exchange between the harbour and open-sea strongly determine the bottom water temperature. Nevertheless, the sea level series are different in the three harbours. In Barcelona and Tarragona, the meteorological tides are more affected by the atmospheric pressure changes; however, in the case of Castellón, which is smaller, the main influence is associated with the wind, which displaces water and causes a convergence when finding land that results in an increase in sea level. Therefore, the results reveal the importance of knowing the dimensions and morphology of each harbour to describe correctly its hydrodynamics because, despite being under comparable climatic conditions due to their geographical proximity, different hydrodynamic responses are observed to similar atmospheric forcings. The low intensities of the currents and the geometric complexity of the harbour domains, compared to open waters, imply that operational forecasting in these domains can present considerable uncertainties if they are not combined with field data.

How to cite: Samper, Y., Liste, M., Mestres, M., Espino, M., Sanchez, A., Sospedra, J., Gonzalez-Marco, D., Ruiz, M. I., and Álvarez, E.: Circulation patterns in northwest mediterranean harbours based on their geometric characteristics., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11100, https://doi.org/10.5194/egusphere-egu21-11100, 2021.

In this study (Wiese et al., 2020) ensemble simulations are performed, in order to assess the significance of the impacts of wave-atmosphere coupling on simulations of both waves and atmospheric models on a regional scale as well as to quantify the internal model variability of both the regional atmospheric model and wave-atmosphere coupled model system. Comparing the magnitude of the internal model variability of the atmospheric model with the internal model variability of the coupled model system shows that the internal model variability can be reduced in the coupled system. While this effect is more pronounced during extreme events, it is still present in a general assessment of the mean internal model variability during the whole study period. Moreover, the impacts of this wave-atmosphere coupling can be distinguished from the internal model variability of the atmospheric model since the effects of the wave-atmosphere interaction are larger than the internal model variability. This study shows that in operational and climate research systems the internal model variability of the atmospheric model is reducible when the ocean waves are coupled to the atmosphere. Clear influences of the wave-atmosphere interaction on both the atmosphere and wave models can be detected and differentiated from the internal model variability. Furthermore, the results of the coupled system have a better agreement with observational data than the results of the reference set up.

References:

Wiese A, Staneva J, Ho-Hagemann HTM, Grayek S, Koch W and Schrum C (2020) Internal Model Variability of Ensemble Simulations With a Regional Coupled Wave-Atmosphere Model GCOAST. Front. Mar. Sci. 7:596843. doi: 10.3389/fmars.2020.596843

How to cite: Wiese, A., Staneva, J., Ho-Hagemann, H. T. M., Grayek, S., Koch, W., and Schrum, C.: Internal Model Variability of a Regional Coupled Wave-Atmosphere Model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12523, https://doi.org/10.5194/egusphere-egu21-12523, 2021.

The Adriatic basin is narrow and elongated with numerous islands and surrounded in many parts by steep orography. Therefore ocean models of the Adriatic Sea should benefit from high-resolution atmospheric forcing that could properly account for orographic variations. We compare the results of long-term hindcasts obtained by using three different atmospheric reanalyses with different spatial resolutions. The CROCO ocean model (formerly ROMS_AGRIF) was configured on a relatively coarse 4 km grid, which we consider fine enough to observe the effects of different forcing resolutions, but still coarse enough that we were able to run multiple simulations in a manageable time. Initial and open boundary conditions were provided by CMEMS Mediterranean Sea Physics Reanalysis, and the model includes 36 freshwater sources. A thorough analysis of several run configurations revealed that spatial resolution should not be the primary criteria in choosing the right forcing, as atmospheric models can be subject to significant biases. These tend to strongly influence the results and sometimes even cause circulation reversals. Here we present the main differences between the runs and also evaluate each of them by comparing the results with satellite observations of sea surface temperature.

How to cite: Vodopivec, M. and Peliz, Á.: 15-year-long Adriatic hindcast: Sensitivity to atmospheric forcing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3297, https://doi.org/10.5194/egusphere-egu21-3297, 2021.

The Regional Ocean Modelling System has been begun to implement for region of Baltic Sea.  A preliminary curvilinear grid with horizontal resolution ca. 2.3 km has been prepared based on the grid, which was used in previous application in our research group (in Parallel Ocean Program and in standalone version of Los Alamos Sea Ice Model - CICE).  Currently the grid has 30 sigma layers, but the final number of levels will be adjusted accordingly.

So far we’ve successfully compiled the model on our machine, run test cases and created Baltic Sea case, which is working with mentioned Baltic grid. The following parameters: air pressure, humidity, surface temperature, long and shortwave radiation, precipitation and wind components are used as an atmospheric forcing. The data arrive from our operational atmospheric model - Weather Research and Forecasting Model (WRF).

Our main goal is to create efficient system for hindcast and forecast simulations of Baltic Sea together with sea ice component by coupling ROMS with CICE. The reason for choosing these two models is an active community that takes care about model’s developments and updates. Authors also intend to work more closely with the CICE model to improve its agreement with satellite measurements in the Baltic region.

Calculations were carried out at the Academic Computer Centre in Gdańsk.

How to cite: Muzyka, M., Jakacki, J., and Przyborska, A.: Application of the Regional Ocean Modelling System (ROMS) for Baltic Sea area, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9612, https://doi.org/10.5194/egusphere-egu21-9612, 2021.

Virtually all modern structured-grid ocean modeling codes are written in orthogonal curvilinear coordinates in horizontal directions, yet the overwhelming majority of modeling studies are done using very simple grid setups - mostly rectangular patches of Mercator grids rotated to proper orientation.  Furthermore, in communities like ROMS, we even observe decline in both interest and skill of creating curvilinear grids over long term.  This is caused primarily by the dissatisfaction with the existing tools and procedures for grid generation due to inability to achieve acceptable level of orthogonality errors.  Clearly, this causes underutilization of full potential of the modeling codes.

To address these issues, a new algorithm for constructing orthogonal curvilinear grids on a sphere for a fairly general geometric shape of the modeling region is implemented as a compile-once - use forever software package.  Theoretically one can use Schwartz-Christoffel conformal transform to project a curvilinear contour onto rectangle, then draw a Cartesian grid on it, and, finally, apply the inverse transform (the one which maps the rectangle back to the original contour) to the Cartesian grid in order to obtain the orthogonal curvilinear grid which fits the contour.  However, in the general case, the forward transform is an iterative algorithm of Ives and Zacharias (1989), and it is not easily invertible, nor it is feasible to apply it to a two-dimensional object (grid) as opposite to just one-dimensional (contour) because of very large number of operations.  To circumvent this, the core of the new algorithm is essentially based on the numerical solution of the inverse problem by an iterative procedure - finding such distribution of grid points along the sides of curvilinear contour, that the direct conformal mapping of it onto rectangle turns this distribution into uniform one along each side of the rectangle.  Along its way, this procedure also finds the correct aspect ratio, which makes it possible to automatically chose the numbers of grid points in each direction to yield locally the same grid spacing in both horizontal directions.  The iterative procedure itself turns out to be multilevel - i.e. an iterative loop built around another, internal iterative procedure.  Thereafter, knowing this distribution, the grid nodes inside the region are obtained solving a Dirichlet elliptic problem.  The latter is fairly standard, except that we use "mehrstellenverfahren" discretization, which yields fourth-order accuracy in the case of equal grid spacing in both directions.  The curvilinear contour is generated using splines (cubic or quintic) passing through the user-specified reference points, and, unlike all previous tools designed for the same purpose, it guarantees by the construction to yield the exact 90-degree angles at the corners of the curvilinear perimeter of grid.

Overall, with the combination of all the new features, it is shown that it is possible to achieve very small, previously unattainable level of orthogonality errors, as well as make it isotropic -- local distances between grid nodes in both directions are equal to each other.

How to cite: Shchepetkin, A.: IZOGRID - A new tool for setting up orthogonal curvilinear grids for oceanic modeling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15325, https://doi.org/10.5194/egusphere-egu21-15325, 2021.

A parallelized unstructured coupled model is developed to investigate wave-current interactions in coastal waters at regional scales. This model links the spectral wave model Simulating Waves Nearshore (SWAN; Booij et al., 1999) with the coastal hydrodynamics shallow-water equation model Thetis (Kärnä et al., 2018). SWAN is based on the action density equations encompassing the various source-terms accounting for deep- and shallow-water phenomena. Thetis solves the non-conservative form of the depth-averaged shallow water equations implemented within Firedrake, an abstract framework for the solution of Finite Element Method (FEM) problems. In resolving wave-current interactions in the proposed model, Thetis predicts water elevation and current velocities which are communicated in SWAN, while the latter provides radiation stresses information for the former. The numerical domain is prescribed by an unstructured mesh allowing higher resolution to areas of interest, while maintaining a reasonable computational cost. As the models share the same mesh, interpolation errors and certain computational overheads can be contained, whereas the choice to employ a sub-mesh for SWAN model is being considered to reduce the overall cost.

The model is initially validated and its performance assessed by a slowly varying-bathymetry. Predictions are compared against the analytical solutions for the wave setup and significant wave height (Longuet-Higgins and Stewart, 1964). Comparisons also extend to results from a coupled 3-D hydrodynamics model with a spectral wave model (Roland et al., 2012). The results of the proposed coupled model exhibit good correlations with the analytical solutions showcasing the same level of efficiency as the 3-D coupled model.

References

[1] Booij N, Ris RC, Holthuijsen LH. A third-generation wave model for coastal regions: 1. Model description and validation. Journal of geophysical research: Oceans 1999;104(C4):7649–7666.

[2] Kärnä T, Kramer SC, Mitchell L, Ham DA, Piggott MD, Baptista AM. Thetis coastal ocean model: discontinuous Galerkin discretization for the three-dimensional hydrostatic equations. Geoscientific Model Development 2018;11(11):4359–4382.

[3] Longuet-Higgins MS, Stewart R. Radiation stresses in water waves; a physical discussion, with applications. In: Deep sea research and oceanographic abstracts, vol. 11 Elsevier; 1964. p. 529–562.

[4] Roland A, Zhang YJ, Wang HV, Meng Y, Teng YC, Maderich V, et al. A fully coupled 3D wave-current interaction model on unstructured grids. Journal of Geophysical Research: Oceans 2012;117(C11).

How to cite: Fragkou, A., Old, C., and Angeloudis, A.: Wave-current interactions representation by coupling spectral wave and coastal hydrodynamics models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-286, https://doi.org/10.5194/egusphere-egu21-286, 2020.

This study evaluates the performance significant wave height hindcast from ECMWF’s latest atmospheric dataset ERA5 in the Mediterranean Sea. Towards this aim, in-situ products from Copernicus Marine Environment Monitoring Service are used. There are nearly 160 observation points along the Mediterranean Sea which are acquired by different institutions with fixed buoys, moorings, and fixed points. The time intervals dating back to 1980s to nowadays, with most of them belongs to the 2000s. To evaluate the verification of ERA5 wave climate with the actual observations, standard statistical metrics such as correlation coefficients (r) are used to compare two datasets in the selected points. The analysis of two time series is done for overlapping time intervals and also for values above a certain threshold, with the purpose of measuring ERA5’s predictive performance of storm conditions. Preliminary results showed that the observations and numerical results of ERA5 are relatively well-matched. The average correlation coefficient is r=0.8 for the selected points which are spatially disperse in the basin. In the Aegean Sea, the coefficient is calculated as r=0.83 between the observations and ERA5, from a moored surface buoy near the Mykonos island with the time coverage of between 2001 and 2019. Some other examples can be given from the Adriatic Sea (r=0.90, 2013-2014), Tyrrhenian Sea (r= 0.96, 2013-2015), Northwestern part of the basin (r=0.71, 2007-2019), and Balearic Sea (r=0.81, 2004-2019).

How to cite: Görmüş, T., Ayat, B., and Aydoğan, B.: Performance evaluation of ECMWF ERA5 Reanalysis waves in the Mediterranean Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1798, https://doi.org/10.5194/egusphere-egu21-1798, 2021.

The ocean is an essential part of the planet that plays a crucial role in the global life system and provides vital resources for humanity. Coastal areas are the most affected by direct pressure from human activity, and their management is very complex due to the multiple interconnected processes that occur there. To conserve and protect our coastal areas, we must observe and understand how they interact. Despite its paramount importance to society, there are fundamental gaps in coastal observing and modelling. Therefore, current forecasting systems limit our capacity to manage this narrow border between land and sea sustainably. Improved numerical models and sustained observations of our ocean are needed to make informed decisions and ensure that human-coastal interaction is sustainable and safe.

EuroSea initiative is an innovation action of the European Union entitled "Improvement and integration of the European oceans Observation and prediction systems for the sustainable use of the oceans'. EuroSea brings together the leading European players in the ocean observation and forecasting with users of oceanographic products and services and provides high-resolution coastal operational prediction systems in domains such as ports, beaches and nearby coastal waters.

In the EuroSea project framework, we present a 3D hydrodynamic tool to improve Barcelona's beaches' inner dynamics solution. We use the Coupled Ocean-Atmosphere - Wave - Sediment Transport (COAWST) Modeling System that utilizes the Model Coupling Toolkit to exchange prognostic variables between the ocean model ROMS, wave model SWAN, and the Community Sediment Transport Modeling System (CSTMS) sediment routines. As part of the system, the wave and ocean models run with nested, refined, spatial grids to provide increased resolution, scaling down to resolve nearshore wave-driven flows, all within selected regions of a larger, coarser-scale coastal modelling system.

Bathymetry was built using a combination of bathymetric data from EMODnet (European Marine Observation and Data Network), and specific high-resolution sources provided by local authorities. Copernicus products have driven these high-resolution simulations.

Results have been validated with field campaigns data, displaying preliminary agreements between model outputs and in-situ observations. The model provides results that will be used to study interactions between sea-level hazards, economic activity, and risk. These results will develop new forecast capabilities, such as erosion and flooding, rip currents, floating debris and flushing times.

Finally, we look ahead to the future of the operational prediction systems as useful tools to make informed decisions, minimize risks and improve environmental management.

How to cite: Liste Muñoz, M., Mestres Ridge, M., Espino Infantes, M., Sánchez-Arcilla, A., García León, M., García Sotillo, M., and Álvarez Fanjul, E.: High-resolution 3D Forecasting System for Barcelona's beaches and coastal waters, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15383, https://doi.org/10.5194/egusphere-egu21-15383, 2021.

The contribution of sea-state-induced processes to sea-level variability is investigated through ocean-wave coupled simulations. These experiments are performed with a high-resolution configuration of the Geestacht COAstal model SysTem (GCOAST), implemented in the Northeast Atlantic, the North Sea and the Baltic Sea which are considered as connected basins. The GCOAST system accounts for wave-ocean interactions and the ocean circulation relies on the NEMO (Nucleus for European Modelling of the Ocean) ocean model, while ocean-wave simulations are performed using the spectral wave model WAM. The objective is to demonstrate the contribution of wave-induced processes to sea level at different temporal and spatial scales of variability. When comparing the ocean-wave coupled experiment with in situ data, a significant reduction of the errors (up to 40% in the North Sea) is observed, compared with the reference. Spectral analysis shows that the reduction of the errors is mainly due to an improved representation of sea-level variability at temporal scales up to 12 h. Investigating the representation of sea-level extremes in the experiments, significant contributions (> 20%) due to wave-induced processes are observed both over continental shelf areas and in the Atlantic, associated with different patterns of variability. Sensitivity experiments to the impact of the different wave-induced processes show a major impact of wave-modified surface stress over the shelf areas in the North Sea and in the Baltic Sea. In the Atlantic, the signature of wave-induced processes is driven by the interaction of wave-modified momentum flux and turbulent mixing, and it shows its impact to the occurrence of mesoscale features of the ocean circulation. Wave-induced energy fluxes also have a role (10%) in the modulation of surge at the shelf break.

How to cite: Bonaduce, A., Staneva, J., Grayek, S., Bidlot, J.-R., and Breivik, Ø.: Sea-state contributions to sea-level variability in the European Seas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12252, https://doi.org/10.5194/egusphere-egu21-12252, 2021.

The quality of estuarine, coastal and marine environment in the Gulf of Tonkin, in the South China Sea, is an essential issue to the ecosystems’ health and to the living conditions and economy of the Viet Nam population. The stakes are particularly high since the demographic density in the Red River delta is one of the highest in the world. Understanding the physical processes that drive the ocean circulation and its response to anthropic pressure there is therefore of primarily importance for enlightened resource management, as well as for designing adequate monitoring and forecasting systems.

As a first step toward a better understanding of the physical coastal and marine environment, we present here a study on the Red river plume variability in the Gulf of Tonkin over the period 2011-2016. The study is based on a numerical simulation, under realistic conditions, using the SYMPHONIE coastal model developed at LEGOS (Marsaleix et al., 2008). Compared with various data sources, the model results show good performances. The river plume is then identified and examined at different time scales. In general, the surface coverage of the river plume is strongly correlated with the runoff but with a 1-month lag. However, in some years, a higher peak in runoff does not create a higher peak of the plume area, suggesting that other forcings need to be taken into account to explain the variability of the river plume.

Using K-mean clustering, the main patterns of the plume are identified. The result shows that the plume has a large variability at both seasonal and interannual scales. Each pattern shows the plume under different forcing conditions.  Most of the time, the plume is narrow and sticks along the coast due to the downcoast current and northeasterly wind. In the summer, due to monsoon, the wind direction changes to southwesterly and helps the plume to spread offshore. The plume reaches its highest coverage in September after the peak of runoff; then its coverage decreases again when the monsoon reverses.

We also analyze events of offshore export of freshwater at daily time scales and show that they can be associated with recurrent coastal eddies during the summer monsoon. We investigate the respective role of wind and runoff in the eddies formation. Comparison with a run without river allows to identify the main impacts of the plume on the ocean states, for example in the current and sea surface elevation.

How to cite: Nguyen, D. T., Ayoub, N., Marsaleix, P., Toublanc, F., De Mey-Fremaux, P., and Ngo Duc, T.: Variability of river plume in the Gulf of Tonkin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2595, https://doi.org/10.5194/egusphere-egu21-2595, 2021.

The final extent of coastal impacts during extreme events depends on a complex combination of factors (coastal morphology, infrastructures, population, economic activities), and meteorological and oceanographic variables interacting at different spatial and temporal scales (e.g.: precipitation, atmospheric pressure, wind, waves, currents and sea level). Coastal sea level is a key driver of most of these impacts, starting by the increased vulnerability of worldwide coastlines due to mean sea level rise. In January 2020, the storm Gloria hit the Western Mediterranean Sea causing severe coastal damages, destruction of infrastructures, flooding and several casualties. The dynamic evolution of sea level during this storm is presented, demonstrating its contribution to the mentioned impacts at different timescales: long-term sea level and seasonal changes, tides and storm surges, and higher frequency oscillations of the order of minutes, associated with different forcing agents like wind-waves, wind and atmospheric pressure variations or edge waves. Tide gauge data are used as the main source of information including the detection and characterization of record-breaking high-frequency oscillations, (infragravity waves, meteotsunamis, resonance effects), thanks to a new software that operationally characterizes these processes from 2Hz raw data. The storm surge component, that also beat the record along Valencia coastline, is analyzed with in-situ data and model outputs from different operational forecasting systems in the region. The exercise shows the difficulty of disentangling different wave, wind and atmospheric pressure contributions to sea level increase during a storm.  

How to cite: Pérez Gómez, B.: On the effect of sea level increases during the Storm Gloria, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13016, https://doi.org/10.5194/egusphere-egu21-13016, 2021.

In micro-tidal coastal systems, the hydrodynamics in fjords reduce to a competition between horizontal density gradient, friction and wind stress. Depending on the depth of the entrance sill, the importance of these factors for water exchange varies within the vertical layer structure of fjords. This study investigates these renewals of water bodies in an isohaline framework, using the example of the Gullmar Fjord on the west coast of Sweden, a transitional area between the brackish Baltic Sea and the northeastern region of the North Sea.

To estimate the influence of wind and baroclinic pumping on volume and salinity transport and their importance on the exchange time scales, a well-validated, realistic, and highly resolved 3D coastal ocean model (GETM) is used, calibrated with especially designed observations. Simulations were combined with passive numerical tracers and evaluated with the mathematical analysis framework of the Total Exhange Flow (TEF).

The results highlight the advantage of isohaline coordinates in the study of water mass transformations within the fjord, compared to geographic coordinates, and the high sensitivity of the exchange flow to sub-grid turbulence.

How to cite: Lange, X. and Jochum, M.: Water exchange and renewal times of a micro-tidal fjord in isohaline coordinates, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14403, https://doi.org/10.5194/egusphere-egu21-14403, 2021.

A comprehensive analysis of the results of remote measurements of the Baltic Sea ice cover has been performed. For this purpose, two modelling integrations were made. Two modelling simulations have been compared with two satellite data sets. As a modelling tool Community Ice Code (CICE) was implemented for Baltic Sea region. It was forced by two independent atmospheric data sets.  In the first simulation, the eBalticGrid system was the source of the atmospheric data, which has been operating in operational mode for almost five years. The second simulation used data from the SatBałtyk system. The satellite data differed in the method of evaluating the quality of the results - in some cases, the result was supervised by ice experts, and in the other, the quality was assessed automatically.  Comparisons with model we have performed using the daily ice concentration and ice thickness maps over the Baltic Sea. Datasets are produced by the Finnish Meteorological Institute (FMI) and disseminated through the central dissemination unit: Copernicus Marine Environment Monitoring Service (CMEMS, http://marine.copernicus.eu/services-portfolio/ access-to-products/). The analysis showed an unnatural increase in the average ice thickness obtained from satellite data at the end of the ice season, for selected regions. The possibility of water appearance on the surface of the analyzed cells was assumed as the source of the potential error, which has a significant impact on the optical properties of the surface. It was proposed to eliminate cells containing a specific surface wetting fraction. However, the results do not allow this approach to be considered correct and therefore the work needs to be continued.

How to cite: Jakacki, J., Muzyka, M., Konik, M., Przyborska, A., and Stramska, M.: Comparison sea ice data for Baltic Sea region based on modelling simulations and remote sensing measurements. , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9635, https://doi.org/10.5194/egusphere-egu21-9635, 2021.

As one of the most productive ecosystems in the world, the Southeastern Pacific Ocean (SPO) coastal zone is economically important to the countries of the region. Dynamically the SPO coastal zone is influenced by the Patagonian Icefields and the large-scale circulation of the open Pacific Ocean, both of which are sensitive to climate change and modes of climate variability, particularly El Niño–Southern Oscillation (ENSO). Due to a paucity of observations, however, the dynamics of this region are still poorly understood.  Here we use the coastal salinity budget as a means of investigating the dynamics of the SPO coastal zone and its relationship with the deeper ocean and Patagonian Icefields, through a combination of high-resolution ocean modelling, satellite observations, and reanalysis data. First, the long-term trends and interannual fluctuations, and their relationship to modes of climate variability are presented. Next, the salinity budget is examined, and the primary balances are quantified. We find that the salinity is primarily governed by the balance between freshwater input and horizontal advection. Finally, we assess the ability of satellite and in-situ observations and reanalysis products to diagnose SPO coastal salinity budget.

How to cite: Zheng, Q. and Bingham, R.: The coastal salinity budget of the Southeastern Pacific Ocean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3075, https://doi.org/10.5194/egusphere-egu21-3075, 2021.

Interactions between atmospheric forcing, topographic constraints to air and water flow, and resonant character of the basin make sea level modeling in Adriatic a challenging problem. In this study we present an ensemble deep-neural-network-based sea level forecasting method HIDRA, which outperforms our setup of the general ocean circulation model ensemble (NEMO v3.6) for all forecast lead times and at a minuscule fraction of the numerical cost (order of 2 × 10^-6). HIDRA exhibits larger bias but lower RMSE than our setup of NEMO over most of the residual sea level bins. It introduces a trainable atmospheric spatial encoder and employs fusion of atmospheric and sea level features into a self-contained network which enables discriminative feature learning. HIDRA architecture building blocks are experimentally analyzed in detail and compared to alternative approaches. Results show the importance of sea level input for forecast lead times below 24 h and the importance of atmospheric input for longer lead times. The best performance is achieved by considering the input as the total sea level, split into disjoint sets of tidal and residual signals. This enables HIDRA to optimize the prediction fidelity with respect to atmospheric forcing while compensating for the errors in the tidal model. HIDRA is trained and analysed on a ten-year (2006-2016) timeseries of atmospheric surface fields from a single member of ECMWF atmospheric ensemble. In the testing phase, both HIDRA and NEMO ensemble systems are forced by the ECMWF atmospheric ensemble. Their performance is evaluated on a one-year (2019) hourly time series from tide gauge in Koper (Slovenia). Spectral and continuous wavelet analysis of the forecasts at the semi-diurnal frequency (12 h)^-1 and at the ground-state basin seiche frequency (21.5 h)^-1 is performed. The energy at the basin seiche in the HIDRA forecast is close to the observed, while our setup of NEMO underestimates it. Analyses of the January 2015 and November 2019 storm surges indicate that HIDRA has learned to mimic the timing and amplitude of basin seiches.

How to cite: Žust, L., Ličer, M., Fettich, A., and Kristan, M.: HIDRA 1.0: Deep-Learning-Based Ensemble Sea Level Forecasting in the Northern Adriatic , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1161, https://doi.org/10.5194/egusphere-egu21-1161, 2021.

High Frequency Radars (HFR) are a mature remote sensing technology which is widely used in ocean observing systems to monitor surface currents in coastal areas.  HFR systems are composed of 2 or more antennas which measure water motion speed along certain bearings, providing radial observations, which are later on postprocessed and mapped to generate orthogonal currents observations (u, v), herein named Totals.

Both Radial and Total observations have been used to correct surface currents through data assimilation in numerous works in the past years, but, in our opinion, there is a lack of studies comparing the performance of both types of data. Here we present a series of experiments evaluating the capabilities of HFR to correct surface currents in the Ibiza Channel using data assimilation. We put special interest in assessing the potentialities of whether using radial or total observations and also their capabilities in a real operational context.

A Lagrangian assessment using a set of 14 surface drifters deployed in the area allows to evaluate the performance of both kinds of observations, showing how the separation distance between drifting buoys and virtual particles is reduced in both cases.

How to cite: Hernandez Lasheras, J., Mourre, B., Orfila, A., Santana, A., Reyes, E., and Tintoré, J.: Comparing High Frequency Radar radial and total derived observations capability to correct surface currents using Data Assimilation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15588, https://doi.org/10.5194/egusphere-egu21-15588, 2021.

Operational morphodynamic modelling is becoming an attractive tool for managers to forecast and reduce coastal risks. The development of highly sophisticated numerical models during the last decades has underpinned the simulation of beach morphological evolution due to wave impacts. However, there are still some fundamental aspects, such as the bathymetric uncertainty, that needs to be regularly updated in the modelling chain to avoid a worthless forecast. It is also very well known that the surf zone is the most highly dynamic area although the bathymetry changes between certain limits. In this work, we explore the influence of bathymetric changes in morphodynamic forecasts. XBEACH is used to model the morphological response of a dissipative urban low-lying sandy coastal stretch (Barcelona, Spain) for different forecasted storms to determine the uncertainty bands of predicted coastal erosion and flooding. We consider as benchmarks the results of XBEACH simulations fed with the bathymetric information taken from existing nautical charts. An analysis of the possible beach states of the studied area following the Wright and Short (1984) is later performed to determine a range of topo-bathymetric configurations that will be used to run the model again. These new simulations are used to determine the uncertainty of the erosion and flooding results. The energy content of the storm in terms of intensity and duration uncertainty is also considered in the analysis. The proposed ensemble approach will serve to determine the likelihood of the modelling forecast outputs. Such statistical characterization is aligned with ensemble forecasting in meteo-oceanographic fields and will provide robust information for coastal decision making, for instance when considering proactive rapid deployment measures against a forecasted storm.

How to cite: Sánchez-Artús, X., Gracia, V., Espino Infantes, M., and Sánchez-Arcilla Conejo, A.: Morphodynamic forecast uncertainty due to bathymetry unknowns, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8696, https://doi.org/10.5194/egusphere-egu21-8696, 2021.

Safe port operations require accurate information on vessel location, routine monitoring and maintenance of navigation channels, and accurate information on coastal hydrodynamics.  Accurate bathymetric data enables port operators to have a high level of confidence in assuring sufficient water depth for vessels, and to effectively direct surveying and dredging operations to maintain navigation routes. However, this is not readily facilitated for nearshore approaches where migrating sandbanks and shoals pose a hazard to shipping.

In this presentation, we present an innovative and novel data assimilation method of combining satellite data, hydrodynamic model (Delft3D) outputs and land-based radar data using machine learning and advanced statistical methods (Dynamic Mode Decomposition). To assimilate these data we use machine learning and statistical methods to detect "patterns" or "modes" in near- and far-field wave climate that are attributable to sub- and intertidal bathymetry and changes therein. We then combine the dominant modes into a low-order representation of the system, providing informed estimates of spatial resolutions and temporal scales where no measurements are physically performed. Satellite data and associated hydrodynamic model outputs are used to provide information on wave direction and height for the offshore-nearshore approaches while land-based marine radar located in the appropriate position provide wave data at higher temporal and more local spatial resolution. 

The data nexus we present in this presentation demonstrates significant improvements in capability above and beyond the use of a given technology in isolation.

How to cite: Phillips, B., Higham, J., Plater, A., Leonardi, N., Arribas-Bel, D., Bird, C., and Sinclair, A.: Assuring safe port navigation by assimilating from data sources with different spatial and temporal scales, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15491, https://doi.org/10.5194/egusphere-egu21-15491, 2021.

The representation of coupled physical processes in coastal models is often constrained and simplified by details of the underlying numerical approach. Ocean, land and river dynamics are generally represented using different computational grids and numerical methods, and are not typically resolved at the fine spatial and temporal scales needed to capture coupled dynamics. In this work, we describe a new 'unified' approach to coupled ocean, land and river modelling, in which all components are represented on a common, multi-scale unstructured mesh, and employ compatible numerical formulations and coupling strategies. In contrast to conventional approaches, this unified approach does not rely on a hierarchy of nested sub-models, but rather leverages the flexibility of unstructured grids to seamlessly embed high-resolution domains within global model configurations. This initiative is an extension of the US Department of Energy's E3SM framework, designed to enhance the representation of coastal dynamics in global-scale ESMs. Initial work on a 'unified' representation of coastal environments is reported, focusing on the development of an unstructured model for the US mid-Atlantic coastal zone as part of the Integrated Coastal Modelling (ICoM) effort.

How to cite: Engwirda, D., Liao, C., Zhou, T., Bisht, G., and Tan, Z.: 'Unified' unstructured ocean, land and river modelling in the coastal zone, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8968, https://doi.org/10.5194/egusphere-egu21-8968, 2021.

In the present work, an investigation on the hydrodynamics of waves and currents interacting at right angle over rough beds has been carried out. The work focuses on the effects of wave motion superposed on the current steady boundary layer, and on how the oscillatory flow affects the current velocity distribution, in the presence of gravel and sand beds.

A laboratory experimental campaign on wave-current orthogonal interaction has been carried out in a shallow water basin at DHI Water and Environment (Hørsholm, Denmark).

Mean flow has been investigated by computing time- and space-averaged velocity profiles. Friction velocity and equivalent roughness have been inferred from the velocity profiles by best fit technique, in order to measure the shear stress experienced by the current mean flow.

Tests in the presence of only current, only waves and combined flow have been performed.

Instantaneous velocities have been Reynolds-averaged to obtain turbulent fluctuations time series and compute turbulence related quantities, such as turbulence intensities and Reynolds stresses.

The analysis of the mean flow revealed a complex interaction of the waves and currents combined flow. Depending on the relative strength of the current with respect to the waves, the superposition of the oscillatory flow may determine an increase or a decrease of the bottom friction experienced by the current.

The superposition of waves always induces an increase of turbulence intensity, except over gravel bed in which a decrease is observed in the very proximity of the bottom. Over gravel bed, the presence of the oscillatory flow determines a decrease of the turbulent intensity gradient, which may be related to the decrease of bottom friction observed in the mean flow analysis.

A turbulence quadrant analysis has been performed and showed that, in the presence of a lone current over a flat gravel bed, the turbulent ejection-sweep mechanism reaches parts of the water column closer to the water surface, similar to what has been observed in the turbulence intensity profiles.

The superposition of the oscillatory flow appears to induce an increment of ejections and sweeps intensity, which is associated with the shear stress increase at the bottom observed in the mean flow analysis. Moreover, a decrease of the number of ejection and sweep events has been recorded, which suggests a suppression of the ejection-sweep events alongside an enhancement of their intensity.

How to cite: Marino, M., Faraci, C., and Musumeci, R. E.: Hydrodynamics of wave-current interaction at a right angle over rough beds, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15120, https://doi.org/10.5194/egusphere-egu21-15120, 2021.

Coastal zone research is becoming increasingly important because the impact of climate change is most significant here. The state of coastal regions is determined by the variability in three contact media (geological, water, and air). Evaluation of level changes on the coasts of various parts of the World Ocean (the Mediterranean, Black, Baltic and North Seas, and the Atlantic coasts in Brazil and France) over a long period of time shows various fluctuations with an upward trend in recent decades.

To highlight the factors that determine the seashores' level fluctuations, three contact media parameters were considered on the example of the western part of the Black Sea. Calculations, analysis, and comparison of trends in the variability of hydrometeorological characteristics (air and water temperatures, precipitation, and river discharge) and sea level over a period of more than 100 years have been carried out.

To assess the intensity of fluctuations of the coastal land along the western coast of the Black Sea, the series of level heights were considered at 6 Ukrainian stations: Vylkove, Chornomorsk (Ilyichevsk), Odesa-port, port Yuzhne, Ochakiv and Sevastopol (partially used as a benchmark), at 2 stations on the Romanian coast: Constanta and Sulina, and 2 stations on the Bulgarian coast: Burgas and Varna. Estimates of the dynamics of the land for the stations of this region's coastal zone for more than a 100-year period are calculated, and it is shown in which way changes in sea level are a consequence of the processes occurring in the coastal land and at the bottom.

Comparison of the years with extreme fluctuations in the sea level with the years of the global El Niño phenomenon showed that one of the causes of the observed disturbances in the water and air environments is the distant manifestations of this phenomenon.

Level fluctuations, both in the Black Sea and in the World Ocean, are synchronous at low-frequency scales (their period is more than 5 years) since global climatic processes on our planet influence them; short-term fluctuations are distinguished by regional features and are created under the influence of local factors (tectonic, geophysical, hydrostatic, etc.).

Modeling and predicting changes in the coastal zone of various parts of the World Ocean requires continuation of systematic observations of sea-level fluctuations, hydrometeorological characteristics, and seismic conditions in regions with the longest data series; it's crucial for the Black Sea as well for the Mediterranean, Baltic, North Seas, and Atlantic shores.

How to cite: Batyrev, O., Andrianova, O., Belevich, R., and Skipa, M.: Coastal zone dynamics - as a result of changes at the border of three environments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5194, https://doi.org/10.5194/egusphere-egu21-5194, 2021.

The objective of this work is to assess the tidal stream energy potential in the Scheldt estuary, through the application of technical specifications from the International Electrotechnical Commission (IEC). The IEC TS 62600-201:2015 establishes a system for analysing and reporting, through estimation or direct measurement, the theoretical tidal current energy resource in oceanic areas including estuaries.

Velocity distribution at the potential deployment site is examined using a high-resolution three-dimensional model of the ocean currents based on the TELEMAC system. The mesh size ranges from 400 m at the mouth of the estuary to 50 m near the potential pilot sites. The unstructured mesh size allows a realistic representation of the detailed bathymetric features, the narrow straits and channels where the most intense currents are. The model is forced at the lateral boundaries with sea surface elevation predicted by the global tidal model Finite Element Solution 2012 (FES 2012) and the river flow from the Scheldt River. The model is calibrated using public data obtained from water level measurements at the ports of Vlissingen, Breskens and Cadzand.

The velocity magnitude and direction calculated over one month at the pilot site are extrapolated over a year by means of a harmonic analysis. At the depth of the tidal current turbine (-2.5m below the sea level), the annual mean of the velocity magnitude is 0.7 m/s with a maximum of 1.6 m/s for the selected pilot site. Velocity magnitudes are in the range of 0.5 to 1 m/s for 54.9% of the time, and above 1 m/s for 17.7% of the time. There are two prevailing directions for the water flow: 47% of current velocity is eastward (direction 70°-90°N) and 46% is westward (direction 250°-260°N). The expected annual energy production is calculated using the modelled velocity distribution and the technical characteristics of the vertical axis water turbine developed by Water2Energy.

The results of this analysis shows that the site has limited potential in terms of energy production.  However, the site could still be relevant as a pilot demonstration site for shorter durations. The analysis based on IEC technical specifications will be useful for the identification and comparison of more energetic sites in the future. Also, this results provides feedback to the IEC on the usability of the technical specification for improvements.

This work is part of the ENCORE project (ENergizing COastal Regions with Offshore Renewable Energy), which aims is to advance four offshore renewable energy technologies through the application of IEC technical specifications in a structured and collaborative process. ENCORE is funded by the European Interreg 2 Seas programme and co-funded by the European Regional Development Fund (ERDF) under grant agreement No 2S08-004.

How to cite: Levasseur, A., Gousset, H., and Le Bris, D.: Estimation of the tidal energy potential in the Scheldt estuary using a three-dimensional unstructured hydrodynamic model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10626, https://doi.org/10.5194/egusphere-egu21-10626, 2021.

The effects of climate change are at the spotlight of scientific research. In coastal science the effects of sea-level rise (SLR) on coastal areas, mainly as a result of melting of ice sheets and thermal volume expansion consist an intensive area of research. As well the changing ocean wave field due to greenhouse effect and interactions of atmospheric processes is under investigation. Researchers have placed focus on significant wave height changes and their associated impacts on the coastal environment, with evidence suggesting that the number, intensity and location of storms will change. It is suggested that equal attention should be placed on the mean wave direction changes and the effects that these changes may have on the coastlines and surrounding coastal infrastructure. Following that, this study investigated the changes in wave direction data since 1979 to 2019 covering 40 years’ time period at 11 offshore UK coastal locations. The selected locations lie close to WaveNet, Cefas’ strategic wave monitoring network points for the UK. Stakeholders use the data to provide advice and guidance to all involved parties including responders and communities about coastal flood risk. On a longer timescale the data provide evidence to coastal engineers and scientists of the wave climate change patterns and the implications this may have on coastal structures and flood defences design. Based on this initiative, this study investigated UK offshore wave climate changes by performing a longer timescale analysis of changes of wave direction patterns. The wave direction data were taken from ECMWF ERA5 6-hour hind cast data catalogue which covers 40 years’ time period from 1797-2019 (Copernicus Climate Change Service (C3S), 2017). MATLAB software coding was primarily utilized for data processing and analyses. Following that, inferential statistics were applied to map inter-decadal statistical changes in wave direction patterns, suggesting that wave directionality patterns have presented changes at 11 offshore locations tested.  The connections of wave directions with North Atlantic Oscillation (NAO) Climatic Index are currently investigated through use of machine learning approaches. The results of this study can be confidently used in wave transformation computational models coupled with hydro-morphodynamic models to downscale offshore wave direction changes to UK coastal areas. This can help identify susceptible coasts to offshore wave climate change. Susceptibility is regarded in form of coastal erosion and accretion rates changes as a result of altered offshore wave conditions, which might affect coastal flood risk with potential impacts on critical infrastructure.  

How to cite: Chatzirodou, A.: Investigation of long-term changes of coastal wave directionality patterns and their connections with NAO climatic index: UK case study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16438, https://doi.org/10.5194/egusphere-egu21-16438, 2021.