Extreme wave height events in NW Spain: a combined multi-sensor and model approach

The Galician coast (NW Spain) is a region that is strongly influenced by the presence of low pressure systems in the mid-Atlantic Ocean and the periodic passage of storms that give rise to severe sea states. Since its wave climate is one of the most energetic in Europe, the objectives of this paper were twofold. The first objective was to characterize the most extreme wave height events in Galicia over the wintertime of a two-year period (2015–2016) by using reliable high-frequency radar wave parameters in concert with predictions from a regional wave (WAV) forecasting system running operationally in the Iberia-Biscay-Ireland (IBI) area, denominated IBI-WAV. The second objective was to showcase the application of satellite wave altimetry (in particular, remote-sensed three-hourly wave height estimations) for the daily skill assessment of the IBI-WAV model product. Special attention was focused on monitoring Ophelia—one of the major hurricanes on record in the easternmost Atlantic—during its 3-day track over Ireland and the UK (15–17 October 2017). Overall, the results reveal the significant accuracy of IBI-WAV forecasts and prove that a combined observational and modeling approach can provide a comprehensive characterization of severe wave conditions in coastal areas and shows the benefits from the complementary nature of both systems.The authors also would like to thank the support by Interreg Atlantic Area project MyCOAST (EAPA 285/2016) co-funded by the ERDF (EU)S

Extreme wave height events in NW Spain: a combined multi-sensor and model approach

The Galician coast (NW Spain) is a region that is strongly influenced by the presence of low pressure systems in the mid-Atlantic Ocean and the periodic passage of storms that give rise to severe sea states. Since its wave climate is one of the most energetic in Europe, the objectives of this paper were twofold. The first objective was to characterize the most extreme wave height events in Galicia over the wintertime of a two-year period (2015–2016) by using reliable high-frequency radar wave parameters in concert with predictions from a regional wave (WAV) forecasting system running operationally in the Iberia-Biscay-Ireland (IBI) area, denominatedIBI-WAV. The second objective was to showcase the application of satellite wave altimetry (in particular, remote-sensed three-hourly wave height estimations) for the daily skill assessment of the IBI-WAV model product. Special attention was focused on monitoring Ophelia—one of the major hurricanes on record in the easternmost Atlantic—during its 3-day track over Ireland and the UK (15–17 October 2017). Overall, the results reveal the significant accuracy of IBI-WAV forecasts and prove that a combined observational and modeling approach can provide a comprehensive characterization of severe wave conditions in coastal areas and shows the benefits from the complementary nature of both systems

Identification of snow and rain at the surface using polarimetric radar

The transition from rain to snow at the surface is one of the challenging facts in aviation and road traffic during winter weather condition. Even though numerical weather forecast is able to provide reasonable forecasts, nowcasting applications still suffer from the precise observation of the transition from rain to snow at the surface. The application of dual-polarization radar has shown that fuzzy logic allows classifying hydrometeors in distinct classes. However, some uncertainty exists in the distinction between light rainfall and light snowfall. The knowledge of temperature can help in this situation, but is often not available with the desired quality and for three-dimensional the region of interest. Further uncertainty is caused by the fact that radar does not measure at the surface but at several hundred meters above the surface. For an improved classification of surface precipitation we identify the height of the melting layer first. The height of the melting layer is then included in the fuzzy classification process. This allows a more reliable distinction between rain (below) and snow (above). In the presentation we will show results from this algorithm using the DLR multi-polarization C-band weather radar POLDIRAD including a verification using ground based observations at Munich airport (disdrometer and human METAR observations) as well as measurements with a vertical pointing Doppler micro rain radar

Projected future changes in tropical cyclone-related wave climate in the North Atlantic

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Impacts of an Altimetric Wave Data Assimilation Scheme and Currents-Wave Coupling in an Operational Wave System: The New Copernicus Marine IBI Wave Forecast Service

The Copernicus Marine IBI-MFC (Iberia–Biscay–Ireland Monitoring and Forecasting Centre) has delivered operational wave forecasts since 2017. The operational application is based on a MFWAM model (Meteo-France WAve Model) set-up, running at a 1/20º grid (5-km). The research presented here was conducted to improve the accuracy of the IBI-MFC wave model products, by means of (i) including a new wave data assimilation scheme and (ii) developing a new coupled ocean-wave modelling framework. Evaluation of these set-up upgrades, in terms of improvements in IBI wave model system capabilities, is here presented. All the model sensitivity test runs, performed for the year 2018, are assessed over the whole IBI domain, using the available in-situ (from 49 mooring buoys) and independent satellite wave observation. The results show that the most relevant improvement is due to the data assimilation, while the impact of surface ocean currents, although less significant, also improves the wave model qualification over the IBI area. The demonstrated benefit, related to the herein proposed upgrades, supported the IBI-MFC decision to evolve its operational wave system, using (since the March 2020 Copernicus Marine Release) the resulting wave model set-up, with data assimilation and currents-wave coupling for operational purposes

New directional wave observations from CFOSAT : impact on ocean/wave coupling in the Southern Ocean

International audienceThe Southern ocean is a complex ocean region with uncertainties related to surface wind forcing and fluxes exchanges at the air/sea interface. The improvement of wind wave generation in this ocean region is crucial for climate studies. With CFOSAT satellite mission, the SWIM instrument provides directional wave spectra for wavelengths from 70 to 500 m, which shed light on the role of correcting the wave direction and peak wave number of dominant wave trains in the wind-waves growth phase. This consequently induced a better energy transfer between waves and a significant bias reduction of wave height in the Southern Ocean (Aouf et al. 2020). The objective of this work is to extend the analysis of the impact of the assimilation of wave number components from SWIM wave partitions on the ocean/wave coupling. To this end, coupled simulations of the wave model MFWAM and the ocean model NEMO are performed during the southern winter period of 2019 (May-July). We have examined the MFWAM/NEMO coupling with and without the assimilation of the SWIM mean wave number components. Several coupling processes related to Stokes drift, momentum flux stress and wave breaking inducing turbulence in the ocean mixing layer have been analyzed. We also compared the coupled runs with a control run without wave forcing in order to evaluate the impact of the assimilation. The results of coupled simulations have been validated with satellite Sea Surface Temperature and available surface currents data over the southern ocean. We also investigated the impact of the assimilation during severe storms with unlimited fetch conditions.Further discussions and conclusions will be commented in the final paper.Aouf L., New directional wave satellite observations : Towards improved wave forecasting and climate description in Southern Ocean, Geophysical Research Letters, DOI: 10.1029/2020GL091187 (in production). What do you want to do ? New mai

Impacts of an Altimetric Wave Data Assimilation Scheme and Currents-Wave Coupling in an Operational Wave System: The New Copernicus Marine IBI Wave Forecast Service

The Copernicus Marine IBI-MFC (Iberia–Biscay–Ireland Monitoring and Forecasting Centre) has delivered operational wave forecasts since 2017. The operational application is based on a MFWAM model (Meteo-France WAve Model) set-up, running at a 1/20º grid (5-km). The research presented here was conducted to improve the accuracy of the IBI-MFC wave model products, by means of (i) including a new wave data assimilation scheme and (ii) developing a new coupled ocean-wave modelling framework. Evaluation of these set-up upgrades, in terms of improvements in IBI wave model system capabilities, is here presented. All the model sensitivity test runs, performed for the year 2018, are assessed over the whole IBI domain, using the available in-situ (from 49 mooring buoys) and independent satellite wave observation. The results show that the most relevant improvement is due to the data assimilation, while the impact of surface ocean currents, although less significant, also improves the wave model qualification over the IBI area. The demonstrated benefit, related to the herein proposed upgrades, supported the IBI-MFC decision to evolve its operational wave system, using (since the March 2020 Copernicus Marine Release) the resulting wave model set-up, with data assimilation and currents-wave coupling for operational purposes

Mud and sand effects on wave propagation over the French Guiana coasts

International audienceThe dampening effect of waves by soft mud layers is observed throughout the spectrum, in laboratory (WELLS & KEMP, 1986) as on the Louisiana or Guyana coasts (WINTERWERP et al., 2007; GENSAC, 2012). Since the bi-layer theoretical approach of GADE (1958), multi parameterizations have been proposed and implemented in wave numerical models (e.g. ROGERS & HOLLAND, 2009) but many efforts of calibrations and additional works are still required to obtain realistic representations of in situ processes. The Guyanese's coast are impacted by the Amazon sediments discharge whose 20 to 30 % migrate longshore either in turbid or in mud banks forms due to the waves and current combined actions (BISCARA, 2016). These mud banks cause rapid coastline variations, leading to accretion, erosion and submersion risks. The French operational wave forecasting system at coastal scale is based on WAVEWATCH III ® (WW3, TOLMAN, 2016), using an unstructured grid that covers Guiana with a resolution of 200 m nearshore. An implementation has been realized in 2017 in the framework of the HOMONIM project (History, Observation, Modeling sea levels, joint SHOM and Météo-France project) for the French Guiana coasts however this version didn't include the effects of the mud and sand banks on waves. In this paper, we evaluate the mud effect on the wave propagation in order to improve the future version of the operational French Guiana configuration. Numerical tests on different parameterizations are performed on a laboratory case, to assess the behaviour of WW3. A more specific application on Guiana is carried out via the creation of a seabed map (grain size) as well as a fine description of the characteristics and location of the mud banks, thanks to high resolution satellite imagery and in-situ data. 1. Introduction Guyana shoreline is characterised by muddy sedimentation fed continuously by deposits brought to the ocean by the Amazon, 800 km further south. At the mouth of the river, this intense sediment load is set in motion by the North Brazilian current and swell, and spread along the coast of Guyana during its ascent to the north. The sediments that are deposited form huge mud banks (up to 5 m thick, 10 to 60 km long, 20 to 30 km wide and 15 to 25 km apart) that migrate rapidly (1 to 5 km.y-1) in low water depth (< 20 m) causing rapid coastline morphological changes which are difficult to predict. The mud banks present on the entire coast of Guyana quickly absorb and dissipate wave energy across the full spectrum (about 70% and more, (WELLS & KEMP, 1986)) and in particular short waves to long waves as long as they pass through the sedimentary body. In the HOMONIM project, the objective is to develop a wave forecasting model in order to better anticipate flooding from the sea and to improve warning systems on French metropolitan and overseas coasts. Initial configurations have been delivered since 2014. For Guiana, a first version was produced in 2016 (V1), based on the WAVEWATCH III ® model using an unstructured grid with a resolution of 200 m nearshore and 8 km offshore. However, this version does not include the effects of sandy and mud banks or current and water level variations on the waves. The objective of this paper is therefore to evaluate the effects of seabed sedimentary characteristics on wave propagation in order to improve the future version of the operational configuration for the French Guiana coastal area. Numerical tests on different parameterizations are performed on the laboratory case of DE WIT (1995), to assess the behaviour of WW3. A more specific application on Guiana during winter storm 2016 is then carried out via the creation of a seabed map as well as a fine description of the characteristics and location of the mud banks, thanks to high resolution satellite imagery and in-situ data