Modelling framework for coastal-scale oceanographic predictions

Ocean Science, 2016

This study addresses the impact of coupling between wave and circulation models on the quality of coastal ocean predicting systems. This is exemplified for the German Bight and its coastal area known as the Wadden Sea. The latter is the area between the barrier islands and the coast. This topic reflects the increased interest in operational oceanography to reduce prediction errors of state estimates at coastal scales, which in many cases are due to unresolved non-linear feedback between strong currents and wind waves. In this study we present analysis of wave and hydrographic observations, as well as results of numerical simulations. A nested-grid modelling system is used to produce reliable nowcasts and short-term forecasts of ocean state variables, including waves and hydrodynamics. The database includes ADCP observations and continuous measurements from data stations. The individual and combined effects of wind, waves and tidal forcing are quantified. The performance of the forec...

Continental Shelf Research, 2014

The high-resolution and coupled forecasting of wind, waves and currents, in restricted coastal domains, offer a number of important challenges; these limit the quality of predictions, in the present state-of-theart. This paper presents the main results obtained for such coastal domains, with reference to a variety of modelling suites and observing networks for: a) Liverpool Bay; b) German Bight; c) Gulf of Venice; and d) the Catalan coast. All of these areas are restricted domains, where boundary effects play a significant role in the resulting inner dynamics. This contribution addresses also the themes of the other papers in this Special Issue, ranging from observations to simulations. Emphasis is placed upon the physics controlling such restricted areas. The text deals also with the transfer to end-users and other interested parties, since the requirements on resolution, accuracy and robustness must be linked to their applications. Finally, some remarks are included on the way forward for coastal oceanography and the synergetic combination of in-situ and remote measurements, with high-resolution 3D simulations.

Advances in Science and Research, 2011

This work compares meteorological results from different regional climate model (RCM) implementations in the Mediterranean area, with a focus on the northern Adriatic Sea. The need to use these datasets as atmospheric forcings (wind and atmospheric pressure fields) for coastal hydrodynamic models to assess future changes in the coastal hydrodynamics, is the basis of the presented analysis. It would allow the assessment of uncertainties due to atmospheric forcings in providing coastal current, surge and wave climate changes from future implementations of hydrodynamic models. Two regional climate models, with different spatial resolutions, downscaled from two different global climate models (whose atmospheric components are, respectively, ECHAM4 and ECHAM5), were considered. In particular, the RCM delivered wind and atmospheric pressure fields were compared with measurements at four stations along the Italian Adriatic coast. The analyses were conducted using a past control period, 1960-1990, and the A1B IPCC future scenario (2070-2100). The chosen scenario corresponds to a world of very rapid economic and demographic growth that peaks in mid-century, with a rapid introduction of new efficient technologies, which balance fossil and non-fossil resources (IPCC, 2007). Consideration is given to the accuracy of each model at reproducing the basic statistics and the trends. The role of models' spatial resolution in reproducing global and local scale meteorological processes is also discussed. The Adriatic Sea climate is affected by the orography that produces a strengthening of north-eastern katabatic winds like bora. Therefore, spatial model resolution, both for orography and for a better resolution of coastline (Cavaleri et al., 2010), is one of the important factors in providing more realistic wind forcings for future hydrodynamic models implementations. However, also the characteristics in RCM setup and parameterization can explain differences between the datasets. The analysis from an ensemble of model implementation would provide more robust indications on climatic wind and atmospheric pressure variations. The scenario-control comparison shows a general increase in the mean atmospheric pressure values while a decrease in mean wind speed and in extreme wind events is seen, particularly for the datasets with higher spatial resolution.

HAL (Le Centre pour la Communication Scientifique Directe), 2021

Submersion risks assessment requires different tools and methods from regional to coastal scales. The SHOM's strategy relies on numerical modelling and observational systems applied in a challenging multi-scale context. At regional scales, storm surge and wave models Hycom and Wavewatch III, bathymetric digital terrain models (DTMs) and observational tide/buoy networks used within the operational national storm surge service (Homonim project with Météo-France) are presented, as well as their applications in climatological 40-year hindasts. At coastal scales, coupling between models at decametric resolutions is required for better forecasting of coastal processes (currents/levels and wave interactions). The aim is to improve knowledge of marine hazards locally, and to develop infra-departmental warning systems based on real time flooding forecasts or statistical risk management tools. The development of such tools requires fine scale topo-bathymetric DTMs and dedicated oceanographic campaigns for model validation. To combine regional to coastal scales and improve numerical performance, the modelling strategy will soon be based on a new numerical model from the TOLOSA library (TOols Library for unstructured Ocean models and Surge Applications). This state-of-the-art numerical code, that handles many types of numerical schemes, physical formalisms and meshes, should lead to ultra-high resolution forecasting capacities, allowing for finer processes studies and forecasts (wave setup, port oscillations, infragravity waves, estuarine dynamics, overflows).

Journal of Marine Science and Technology

The objective of the present work is to illustrate the performances of the numerical wave models in ocean and coastal environment. Third generation wave models are considered nowadays the most appropriate for such task. These are full spectral models based on the integration on the wave energy (or alternatively wave action) balance equation. In order to cover more aspects related with the modelling process hindcast, nowcast and forecast schemes are discussed and illustrated along six case studies. The major model used was SWAN (acronym for Simulating Waves Nearshore) which is a very flexible model that can be applied in a wide range of coastal applications being effective from high resolution coastal areas up to quasi oceanic scales. In both hindcasts and forecasts the wave forcing was provided by generation models (WAM and WW3), while in nowcast schemes buoy data were used. Various coastal environments that are rather different from the point of view of the bathymetric features and of the characteristics of the environmental matrix were considered. These are the Portuguese continental nearshore with higher resolution sub domains, Madeira Archipelago, the nearshore of Sardinia Island in the Mediterranean Sea and the Black Sea. A general conclusion of this work would be that, despite some limitations, the wave models provide an effective framework in predicting wave conditions in ocean and coastal environment.

Natural Hazards and Earth System Sciences Discussions, 2016

SANIFS (Southern Adriatic Northern Ionian coastal Forecasting System) is a coastal-ocean operational system based on the unstructured-grid finite-element three-dimensional hydrodynamic SHYFEM model and providing short-term forecasts. The operational chain is based on a downscaling approach starting from the large-scale system for the entire Mediterranean basin (MFS, Mediterranean Forecasting system), which provides initial and boundary condition fields to the nested system. The model is configured to provide hydrodynamics and active tracer forecasts both in open ocean and coastal waters of Southeastern Italy using a variable horizontal resolution from 3-4 km in the open sea to 500-50 m in the coastal areas. Given that the coastal fields are driven by a combination of both local/coastal and deep ocean forcings propagating along the shelf, the performance of SANIFS was verified both in forecast and simulation mode, first (i) at the large and shelf-coastal scales by comparing with a large scale survey CTD in the Gulf of Taranto and then (ii) at the coastal-harbour scale (Mar Grande of Taranto) by comparison with CTD, ADCP and tide gauge data. Sensitivity tests were performed on initialization conditions (mainly focused on spin-up procedures) and on surface boundary conditions by assessing the reliability of two alternative datasets at different horizontal resolution (12.5 and 6.5 km). The SANIFS forecasts at a lead-time of one day were compared with the MFS forecasts highlighting that SANIFS is able to retain the large scale dynamics of MFS. Those get correctly propagated to the shelf-coastal scale improving the forecast accuracy (+17% for temperature and +6% for salinity compared to MFS). Moreover the added value of SANIFS was assessed at coastal-harbour scale, which is not covered by the coarse resolution of MFS, where the SANIFS forecasted fields well reproduced the observations (temperature RMSE equal to 0.11°C). Furthermore SANIFS simulations were compared with hourly time-series of temperature, sea level and velocity measured at the coastal-harbour scale showing a good agreement. Simulations in the Gulf of Taranto described a circulation mainly characterized by an anticyclonic gyre with the presence of cyclonic vortexes in shelf-coastal areas. A surface water inflow from open sea to Mar Grande characterizes the coastal-harbour scale.

Ocean Modelling, 2016

A region of freshwater influence (ROFI) under hypertidal conditions is used to demonstrate inherent problems for nested operational modelling systems. Such problems can impact the accurate simulation of freshwater export within shelf seas, so must be considered in coastal ocean modelling studies. In Liverpool Bay (our UK study site), freshwater inflow from 3 large estuaries forms a coastal front that moves in response to tides and winds. The cyclic occurrence of stratification and remixing is important for the biogeochemical cycles, as nutrient and pollutant loaded freshwater is introduced into the coastal system. Validation methods, using coastal observations from fixed moorings and cruise transects, are used to assess the simulation of the ROFI, through improved spatial structure and temporal variability of the front, as guidance for best practise model setup. A structured modelling system using a 180 m grid nested within a 1.8 km grid demonstrates how compensation for error at the coarser resolution can have an adverse impact on the nested, high resolution application. Using 2008, a year of typical calm and stormy periods with variable river influence, the sensitivities of the ROFI dynamics to initial and boundary conditions are investigated. It is shown that accurate representation of the initial water column structure is important at the regional scale and that the boundary conditions are most important at the coastal scale. Although increased grid resolution captures the frontal structure, the accuracy in frontal position is determined by the offshore boundary conditions and therefore the accuracy of the coarser regional model.

Natural Hazards and Earth System Sciences, 2008

This paper reviews the characterization of wave storms along the Spanish/Catalan Mediterranean coast. It considers the "physical" and "statistical" description of wave parameters and how they are affected by the prevailing meteo patterns and the sharp gradients in orography and bathymetry. The available field data and numerically simulated wave fields are discussed from this perspective. The resulting limits in accuracy and predictability are illustrated with specific examples. This allows deriving some conclusions for both short-term operational predictions and a longterm climatic assessment.

Operational Oceanography in the 21st Century, 2011

In coastal oceanography, simulation models are used to a variety of ends. Idealized studies may address particular dynamical processes or features of coastline and bathymetry; reproducing the circulation in a geographical region can compliment studies of ecosystems and geomorphology; and models may be employed to simulate observing systems and to forecast oceanic conditions for practical operational needs. Frequently, the interplay between multiple forcing mechanisms, geographic detail, stratification, and nonlinear dynamics, is significant, and this demands that ocean models for coastal applications are capable of representing a comprehensive suite of dynamical processes. Drawing on a series of recent modelbased studies of the inner to mid-shelf region of the Middle Atlantic Bight (MAB) we illustrate, by example, these methodologies and the breadth of dynamical processes that influence coastal ocean circulation. We demonstrate that the recent introduction of variational methods into coastal ocean simulation is a development that greatly enhances our ability to integrate models with data from the evolving coastal ocean observatories for the purposes of improved ocean prediction, adaptive sampling and observing system design.

Continental Shelf Research, 2009

We revisit the surge of November 1977, a storm event which caused damage on the Sefton coast in NW England. A hindcast has been made with a coupled surge-tidewave model, to investigate the effects of waves on the surge generation by modifying the surface drag. The POLCOMS-WAM modelling system has been used to model combined tides, surges, waves and wave-current interaction in the Irish Sea on a 1.85km grid. This period has been previously thoroughly studied e.g. Jones and Davies (1998) and has been chosen here to validate the POLCOMS-WAM model to test the accuracy of surge elevation predictions in the study area. A one-way nested approach has been set up. It was demonstrated that (as expected) swell from the North Atlantic does not have a significant impact in the eastern Irish Sea. To capture the external surge generated outside of the Irish Sea a (1/9º by 1/6º) model extending beyond the continental shelf edge was run using the POLCOMS model for tide and surge.