Proudman Oceanographic Laboratory Research Articles

Ecoregions in the Mediterranean Sea Through the Reanalysis of Phytoplankton Functional Types and Carbon Fluxes

AbstractIn this work we produced a long‐term reanalysis of the phytoplankton community structure in the Mediterranean Sea and used it to define ecoregions. These were based on the spatial variability of the phytoplankton type fractions and their influence on selected carbon fluxes. A regional ocean color product of four phytoplankton functional types (PFTs; diatoms, dinoflagellates, nanophytoplankton, and picophytoplankton) was assimilated into a coupled physical‐biogeochemical model of the Mediterranean Sea (Proudman Oceanographic Laboratory Coastal Ocean Modelling System‐European Regional Seas Ecosystem Model, POLCOMS–ERSEM) by using a 100‐member ensemble Kalman filter, in a reanalysis simulation for years 1998–2014. The reanalysis outperformed the reference simulation in representing the assimilated ocean color PFT fractions to total chlorophyll, although the skill for the ocean color PFT concentrations was not improved significantly. The reanalysis did not impact noticeably the reference simulation of not assimilated in situ observations, with the exception of a slight bias reduction for the situ PFT concentrations, and a deterioration of the phosphate simulation. We found that the Mediterranean Sea can be subdivided in three PFT‐based ecoregions, derived from the spatial variability of the PFT fraction dominance or relevance. Picophytoplankton dominates the largest part of open ocean waters; microphytoplankton dominates in a few, highly productive coastal spots near large‐river mouths; nanophytoplankton is relevant in intermediate‐productive coastal and Atlantic‐influenced waters. The trophic and carbon sedimentation efficiencies are highest in the microphytoplankton ecoregion and lowest in the picophytoplankton and nanophytoplankton ecoregions. The reanalysis and regionalization offer new perspectives on the variability of the structure and functioning of the phytoplankton community and related biogeochemical fluxes, with foreseeable applications in Blue Growth of the Mediterranean Sea.

The CO5 configuration of the 7 km Atlantic Margin Model: large-scale biases and sensitivity to forcing, physics options and vertical resolution

Abstract. We describe the physical model component of the standard Coastal Ocean version 5 configuration (CO5) of the European north-west shelf (NWS). CO5 was developed jointly between the Met Office and the National Oceanography Centre. CO5 is designed with the seamless approach in mind, which allows for modelling of multiple timescales for a variety of applications from short-range ocean forecasting to climate projections. The configuration constitutes the basis of the latest update to the ocean and data assimilation components of the Met Office's operational Forecast Ocean Assimilation Model (FOAM) for the NWS. A 30.5-year non-assimilating control hindcast of CO5 was integrated from January 1981 to June 2012. Sensitivity simulations were conducted with reference to the control run. The control run is compared against a previous non-assimilating Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS) hindcast of the NWS. The CO5 control hindcast is shown to have much reduced biases compared to POLCOMS. Emphasis in the system description is weighted to updates in CO5 over previous versions. Updates include an increase in vertical resolution, a new vertical coordinate stretching function, the replacement of climatological riverine sources with the pan-European hydrological model E-HYPE, a new Baltic boundary condition and switching from directly imposed atmospheric model boundary fluxes to calculating the fluxes within the model using a bulk formula. Sensitivity tests of the updates are detailed with a view toward attributing observed changes in the new system from the previous system and suggesting future directions of research to further improve the system.

Modeling flocculation in a hypertidal estuary

When fine particles are involved, cohesive properties of sediment can result in flocculation and significantly complicate sediment process studies. We combine data from field observations and state-of-the-art modeling to investigate and predict flocculation processes within a hypertidal estuary. The study site is the Welsh Channel located at the entrance of the Dee Estuary in Liverpool Bay. Field data consist of measurements from a fixed site deployment during 12–22 February 2008. Grain size, suspended sediment volume concentration, and current velocity were obtained hourly from moored instruments at 1.5 m above bed. Near-bottom water samples taken every hour from a research vessel are used to convert volume concentrations to mass concentrations for the moored measurements. We use the hydrodynamic model Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS) coupled with the turbulence model General Ocean Turbulence Model (GOTM) and a sediment module to obtain three-dimensional distributions of suspended particulate matter (SPM). Flocculation is identified by changes in grain size. Small flocs were found during flood and ebb periods—and correlate with strong currents—due to breakup, while coarse flocs were present during slack waters because of aggregation. A fractal number of 2.4 is found for the study site. Turbulent stresses and particle settling velocities are estimated and are found to be related via an exponential function. The result is a simple semiempirical formulation for the fall velocity of the particles solely depending on turbulent stresses. The formula is implemented in the full three-dimensional model to represent changes in particle size due to flocculation processes. Predictions from the model are in agreement with observations for both settling velocity and SPM. The SPM fortnight variability was reproduced by the model and the concentration peaks are almost in phase with those from field data.

Effect of High-Resolution Meteorological Forcing on Nearshore Wave and Current Model Performance

Abstract Accurate representation of wind forcing and mean sea level pressure is important for modeling waves and surges. This is especially important for complex coastal zone areas. The Weather Research and Forecasting (WRF) model has been run at 12-, 4-, and 1.33-km resolution for a storm event over the Irish Sea. The outputs were used to force the coupled hydrodynamic and the Proudman Oceanographic Laboratory Coastal Ocean Modeling System (POLCOMS)–Wave Model (WAM) and the effect on storm surge and waves has been assessed. An improvement was observed in the WRF model pressure and wind speed when moving from 12- to 4-km resolution with errors in wind speed decreasing more than 10% on average. When moving from 4 to 1.33 km no further significant improvement was observed. The atmospheric model results at 12 and 4 km were then applied to the ocean model. Wave direction was seen to improve with increased ocean model resolution, and higher-resolution forcing was found to generally increase the wave height over the Irish Sea by up to 40 cm in places. Improved clustering of wave direction was observed when 4-km meteorological forcing was used. Large differences were seen in the coastal zone because of the improved representation of the coastline and, in turn, the atmospheric boundary layer. The combination of high-resolution atmospheric forcing and a coupled wave–surge model gave the best result.

Modelling temperature and salinity in Liverpool Bay and the Irish Sea: sensitivity to model type and surface forcing

Abstract. Three shelf sea models are compared against observed surface temperature and salinity in Liverpool Bay and the Irish Sea: a 7 km NEMO (Nucleus for European Modelling of the Ocean) model, and 12 km and 1.8 km POLCOMS (Proudman Oceanographic Laboratory Coastal Ocean Modelling System) models. Each model is run with two different surface forcing datasets of different resolutions. Comparisons with a variety of observations from the Liverpool Bay Coastal Observatory show that increasing the surface forcing resolution improves the modelled surface temperature in all the models, in particular reducing the summer warm bias and winter cool bias. The response of surface salinity is more varied with improvements in some areas and deterioration in others. The 7 km NEMO model performs as well as the 1.8 km POLCOMS model when measured by overall skill scores, although the sources of error in the models are different. NEMO is too weakly stratified in Liverpool Bay, whereas POLCOMS is too strongly stratified. The horizontal salinity gradient, which is too strong in POLCOMS, is better reproduced by NEMO which uses a more diffusive horizontal advection scheme. This leads to improved semi-diurnal variability in salinity in NEMO at a mooring site located in the Liverpool Bay ROFI (region of freshwater influence) area.

Obtaining instantaneous water levels relative to a geoid with a 2D storm surge model

Current and new applications of 2D storm surge models such as the Dutch Continental Shelf Model (DCSM) require that the models provide proper estimates of the instantaneous water levels expressed relative to a particular geoid, rather than only the tide and surge components expressed relative to the ill-defined model's zero height surface. For DCSM, this is realized by adding the depth-averaged horizontal baroclinic pressure gradients to the model equations, which are derived from 4D salinity and temperature fields provided by the Proudman Oceanographic Laboratory hydrodynamic model (POL's hindcast). The vertical datum of the extended model is fixed to that of the European Gravimetric Geoid model 2008 (EGG08). This is done by an adjustment of the model parameters that depend on the choice of the reference surface (e.g., bathymetry) and by referring the water levels along the open boundaries to this reference surface. Using different numerical experiments we investigate the effects on the water levels of several approximations we have made during the implementation. The ability of the model to reproduce both the mean sea level (MSL) and instantaneous water levels is assessed by a comparison with the MSL derived from POL's hindcast as well as with instantaneous water levels acquired by various radar altimeter satellites. From this comparison we conclude that our modeled MSL is in good agreement with the MSL derived from POL's hindcast; the standard deviation of the differences is below 2cm. However, larger differences in MSL are observed when comparing the model output with the MSL derived from radar altimeter data. They are attributed to either geoid errors or errors in the used salinity and temperature fields. The root mean squared (rms) differences between observed and modeled instantaneous water levels over the entire model domain varies from 9cm for data acquired by the TOPEX satellite to 11cm for data acquired by the GFO-1 satellite. These numbers improve to 8–10cm on the North Sea, for data acquired by the TOPEX and ERS-2 satellites, respectively. These numbers are a factor two to three larger than the expected accuracy of water levels derived from radar altimeter data (which is ∼4cm). About 25% of these differences can be explained by a bias between the modeled and observed water levels of a single satellite pass. These biases are attributed to errors in the applied correction for the net steric expansion/contraction of the global oceans as this is not captured by DCSM that makes use of the Boussinesq approximation, as well as other errors in model and data.

Remote sensing of seasonal stratification dynamics in the southern Irish Sea

In early summer, a well-defined front forms at the southern boundary of Irish Sea between thermally stratified and tidally mixed waters. The Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS) was used to predict the location of this front, and data from the MODIS Aqua sensor was used to derive a five-year time series of red-waveband remote sensing reflectance (Rrs667) and sea surface temperature (SST) for two representative areas on either side of the frontal region. Pronounced annual cycles in Rrs667 and SST were observed at both locations, with summer minima in Rrs667 being roughly coincident with SST maxima. Previous studies have shown that Rrs667 in the Irish Sea is mainly determined by near-surface concentrations of suspended mineral particles. The annual cycles in reflectance therefore indicate that vertical mixing of the water column in winter supplies fine particles to the surface layer which settle out in calmer summer conditions. While the temporal resolution achievable by remote sensing in a single year was limited by the high incidence of cloud cover, monthly averaged data for the whole five-year period revealed differences of the order of one month in the timing of the reflectance cycle on the mixed and stratified sides of the front. This difference produced transient patterns of reflectance in early summer (and occasionally in autumn) in which sharp contrasts coincided with the location of the tidal front predicted by the POLCOMS model. We conclude that optical remote sensing in shelf seas can provide information not only on changing concentrations of optically significant materials, but also on the location and timing of dynamical processes such as seasonal front formation, and note that such information is of potential value for tuning and validating numerical models of shelf sea ecosystems.

Detecting storm surge loading deformations around the southern North Sea using subdaily GPS

SUMMARY A large storm surge event occurred on 2007 November 2009 in the southern North Sea where strong winds caused the sea level to rise drastically by up to 3 m within several hours. Based on the Proudman Oceanographic Laboratory storm surge model, the predicted loading displacements at coastal stations can reach a few centimetres in the vertical and several millimetres in the horizontal directions. In this study, we used two-hourly global positioning system (GPS) positions at 26 stations around the southern North Sea to identify the loading displacements caused by this storm surge event. We find that the mean rms of the differences between the estimated and predicted displacements are 4.9, 1.3 and 1.4 mm, which are insignificant compared to the one-sigma GPS positioning errors of 5.1, 2.0 and 2.4 mm for the Up, East and North components, respectively. More interestingly, in both vertical and horizontal directions, the estimated displacements successfully tracked the temporal evolution ofthestormsurgeloadingeffects.Inaddition,withinthewholeof2007November,weusedthe predicted displacements to correct the two-hourly GPS positions, and consequently reduced the rms of the estimated displacements on average from 9.3, 3.0 and 2.9 mm to 7.8, 2.8 and 2.8 mm for Up, East and North components, respectively. Therefore, subdaily loading effects due to storm surges should be paid attention to in the GPS positioning that contributes to crustal-motion studies around shallow seas such as the North Sea, the Baltic Sea and the Gulf of Mexico.

Multi-decadal variability and trends in the temperature of the northwest European continental shelf: A model-data synthesis

We examine the trends and variability in temperature of the northwest European shelf seas over the period 1960–2004 using four approaches: a regional model simulation (using the Proudman Oceanographic Laboratory Coastal Ocean Modelling System; POLCOMS), in situ multi-annual timeseries observations, satellite remote sensed (AVHRR) sea surface temperature (SST), and an analysis of data held in an international database at the International Council for the Exploration of the Sea (ICES). We focus on variability for the full period and trends from 1985 to 2004, being limited by the length of model simulation and the availability of satellite data. We find that all data sources give a consistent picture, with both trends and variability being intensified on-shelf and north of ∼48°N. The model and AVHRR SST show statistically significant warming trends in large areas of this region that are clearly distinguishable from both model/observation error and natural variability on these timescales. This ‘signal to noise ratio’ is substantially reduced when near bottom temperatures are considered in the model. The long timeseries at Port Erin (Isle of Man) shows that the variation in trend is well represented by the model and that the warming trend in the period 1985–2004 is substantially larger and of longer duration than previous peaks in 20-year trends since 1914.We find that the SST trends are greater in the model and satellite observations than the air temperature trends in the ERA40 re-analysis used for forcing; the net sea to air heat flux is ∼20% less in 1985–2004 than 1960–1984 (including shortwave, longwave, sensible and latent components). This is partly compensated by a ∼9% reduction in advective warming. The model shows the trends in seasonally stratified regions are greater at the surface than at depth, indicating an increase in this stratification. While this pattern is also seen in the annual trends from the ICES data analysis, the lack of seasonal resolution hampers a quantitative corroboration.The model is seen to have good skill in reproducing both the trends and variability, but tends to underestimate the trends. The modelled variability is overestimated in some coastal and open ocean regions and underestimated elsewhere, while the phase of this variability is generally well represented. Generally the model performance is better on-shelf than in the open ocean.

The tide predictions for D-Day

Based on the physics of Newton and Laplace, the big brass tide-predicting machine designed by Lord Kelvin was crucial for the success of the Normandy invasion in World War II.

Impact of sediment-induced stratification and turbulence closures on sediment transport and morphological modelling

Appropriate descriptions of turbulence are important in predicting sediment transport and seabed evolution. We use here a three-dimensional model to investigate the impacts of sediment-induced stratification, erosion parameterization, and turbulence closures on sediment transport and morphological simulations. The model is implemented in the Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS), which couples a hydrodynamic model to the General Ocean Turbulence Model (GOTM) and to a sediment transport model. This sediment transport model calculates both suspended sediment concentrations and bed evolution. A large number of turbulence closures can be tested and we focus on the methods used to calculate the turbulent length scale and the stability functions. Different modelling scenarios are assessed against experimental data of velocity profiles, suspended sediment concentrations, and trench migration in a laboratory flume. Numerical results show that the processes investigated have little impact on the flow velocity profiles, in spite of some differences on the bed shear stress. The only exception is the one-equation turbulence closure, which cannot reproduce velocity profiles appropriately. Sediment-induced stratification, erosion parameterization, and turbulence closures can all have significant impacts on the suspended sediment concentration and the bed evolution. Model-data comparisons are found to be particularly sensitive to the method used to calculate the turbulent length scale.

Impact assessment of advanced coupling features in a tide–surge–wave model, POLCOMS-WAM, in a shallow water application

Tide–surge–wave interaction is important in determining the nearshore 3D-current profile and the total water elevation. Liverpool Bay, northwest England, is used to assess the impact of coupling the 3rd generation spectral WAve Model (WAM), modified for shallow water, to the Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS), a tide–surge model, through 2-way interactions. Data are readily available from the Irish Sea Observatory to quantify the importance of each coupled term with the aim of producing the most accurate model setup for coastal forecasting. A storm event, 18th January 2007, has been hindcast to investigate extreme tide–surge–wave condition both offshore and inshore. The coupled terms investigated include standard processes already included (bottom friction, surface stress and the Doppler shift of the waves by the depth-averaged current), as well as advanced coupling procedures: use of the 3D current in the wave physics and calculation of radiation stress and Stokes' drift. During storm conditions it is found that the radiation stress is the most important term in this shallow water application as wave-setup increases coastal flood risk. However, WAM runs in near real time, making this model only practical for research purposes. Further work is therefore required to simplify this model setup.

INFLUENCE OF TURBULENCE CLOSURE ON ESTUARINE SEDIMENT DYNAMICS AND MORPHODYNAMICS

Turbulence significantly impacts hydrodynamics, mixing and sediment dynamics in coastal environments. We employ a three-dimensional model, the Proudman Oceanographic Laboratory Coastal Ocean Modeling System (POLCOMS), to investigate the effects of implementing various turbulence closure schemes on sediment dynamics and morphodynamics. This model is applied to an idealized estuary, which is represented by a straight rectangular basin. A simple tidal flow is forced at one end and a constant river flow is imposed at the other. Most of the turbulence closure schemes employed are implemented via coupling to the General Ocean Turbulence Model (GOTM). Their effects are also compared to the impact of different erosion parameterizations on the numerical results and observed for different sediment properties.

The potential impacts of climate change on the hydrography of the northwest European continental shelf

Changes in global atmospheric conditions have the potential to substantially influence shelf sea environments with far reaching consequences for their ecosystems. Here we focus on the northwest European continental shelf, and review the mechanisms by which climate change might affect the temperature, salinity and stratification of this shelf sea. We explore results from a single pair of Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS) simulations forced by the Hadley Centre regional climate model, for conditions typical of 1961–1990 and 2070–2098, under a ‘business as usual’ emissions scenario (SRES A1B). This provides a single, physically plausible, representation of the future and a consistent representation of the recent past. Comparing these simulations, the shelf sea regions of this model are shown to warm substantially more than the open-ocean, by between 1.5 and 4 °C depending on location. Across the whole domain the surface waters are projected to be ∼0.2 p.s.u. fresher by the end of the 21st century. The strength of seasonal stratification is shown to increase by ∼20% on the shelf, compared with 20–50% in the open-ocean. The former being controlled by temperature and the latter by salinity. In shelf seas away from the direct influence of river discharge, stratification is projected to start ∼5 days earlier and breakdown ∼5–10 days later each year, hence extending the stratified period. An ERA-40 re-analysis forced simulation provides a reference, along with validation from gridded monthly mean data from the ICES data base.

An investigation of recent decadal‐scale storm events in the eastern Irish Sea

The Proudman Oceanographic Laboratory Coastal Modelling System coupled to the WAve Model (POLCOMS‐WAM) modeling system has been used to model combined tides, surges, waves, and wave‐current interaction in the Irish Sea on a 1.85 km grid. A method for data analysis is presented to determine what factors and interactions contribute to extreme conditions in a region of interest. An 11 year hindcast (1996–2006) has been performed to investigate the meteorological conditions that cause extreme surge and/or wave conditions in Liverpool Bay. A one‐way nested model approach was used. For waves, a 1° North Atlantic WAM model forces the boundary of the Irish Sea model, driven by ERA‐40 wind (∼1° resolution every 6 h). To capture the external surge generated outside of the Irish Sea, the (1/9° × 1/6°) Proudman Operational surge model extending to the continental shelf edge was run for tide and surge and was forced by Met Office mesoscale winds (∼12 km resolution every hour). The data implied that the largest surges at Liverpool are generally driven by winds from the south to the west while the largest waves are forced by winds from the west to the northwest. The worst storm conditions in Liverpool Bay result under southwesterly wind conditions that veer to the west. The large tidal range in the region acts to enhance the impact of the surge through tide‐surge interaction. Moreover, the highest water levels in Liverpool Bay are in response to southwesterly winds combined with high‐water spring tide. Even though no significant surge occurs at this time, the flood threat is at its greatest.

A case study of combined wave and water levels under storm conditions using WAM and SWAN in a shallow water application

Extreme storm events in Liverpool Bay, UK, are under investigation. A recent storm, 18th January 2007, has been used to investigate different modelling approaches to accurately simulate wave–surge conditions in shallow water. In Liverpool Bay wave and surge influence and their interaction are often considered in many studies. The tide–surge–wave interaction has been modelled in the Irish Sea using the Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS) coupled to the state-of-the-art 3rd generation spectral WAve Model (WAM). Waves are locally generated in Liverpool Bay, while the surge is locally and externally generated. To include the external surge the 1.8 km Irish Sea model has been nested, using a 1-way approach, into the 1/9° by 1/6° operational Continental Shelf surge model. To investigate the performance of POLCOMS–WAM in shallow water a 180 m Liverpool Bay model has been nested within the Irish Sea model. For this high resolution model the state-of-the-art 3rd generation Simulating WAves Nearshore (SWAN) spectral model is used to further develop WAM, modified for shallow water. A POLCOMS–WAM and POLCOMS–SWAN (1-way) coupled model has been implemented to assess the effects of tide–surge–wave interaction at the coast. Investigation of the significant wave height and surge elevation reveals that when modified for shallow water WAM performs as well as SWAN. Two-way coupling between POLCOMS–WAM allows wave-setup to be included in the surge prediction greatly improving the hydrodynamic result. A drawback to using WAM is the computational expense, making SWAN more suitable for simulations exceeding a few days in duration.

An 11-year validation of wave-surge modelling in the Irish Sea, using a nested POLCOMS–WAM modelling system

In the future it is believed that extreme coastal flooding events will increase (in frequency and intensity) as a result of climate change. We are investigating the flood risks in the eastern Irish Sea posed by extreme storm events. Here, an 11-year simulation (01/01/1996–01/01/2007) including wave–current interaction has been validated. These data can then be used to investigate the potential for coastal flooding in the study area. To accurately model a storm event in the eastern Irish Sea both wave effects and the influence of the external surge need to be considered. To simulate the waves, we have set up a one-way nested approach from a 1° North Atlantic model, to a 1.85 km Irish Sea model, using the state-of-the-art 3rd-generation spectral WAve Model (WAM). This allows the influence of swell to be correctly represented. The Proudman Oceanographic Laboratory Coastal-Ocean Modelling System (POLCOMS) has been used to model the tide–surge interaction. To include the external surge we have set up a one-way nested approach from the 1/9° by 1/6° operational Continental Shelf surge model, to a 1.85 km Irish Sea model. For the high resolution Irish Sea model we use a POLCOMS–WAM coupled model, to allow for the effects of wave–current interaction on the prediction of surges at the coast. Using two classification schemes the coupled model is shown to be good and often very good at predicting the surge, total water elevation and wave conditions. We also find the number of low level surge events has increased in the study area over the past decade. However, this time period is too short to determine any long-term trends in the wave and surge levels.

Surge modelling in the eastern Irish Sea: present and future storm impact

It is believed that, in the future, the intensity and frequency of extreme coastal flooding events may increase as a result of climate change. The Natural Environment Research Council (NERC) Flood Risk from Extreme Events (FREE) project, Coastal Flooding by Extreme Events and EU FP7 Morphological Impacts and Coastal Risks Induced by Extreme Storm Events project are investigating the flood risks in the eastern Irish Sea, an area that includes most of England’s coastal types. Using a previously modelled and validated historical extreme surge event, in November 1977, we now investigate the changes in peak surge as a result of possible future climate conditions. In order to simulate the surge, we have set up a one-way nested approach, using the Proudman Oceanographic Laboratory Coastal Ocean Modelling System 3D baroclinic model, from a domain covering the whole NW European continental shelf, through to a 1.85 km Irish Sea model; both areas are forced by tides, atmospheric pressure and winds. We use this modelling system to investigate the impact of enhanced wind velocities and increased sea levels on the peak surge elevation and residual current pattern. The results show that sea level rise has greater potential to increase surge levels than increased wind speeds.

Coupled wave and surge modelling for the eastern Irish Sea and implications for model wind-stress

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-tide-wave model, to investigate whether a wave-dependent surface drag is necessary for accurate surge prediction, and also if this can be represented by an optimised Charnock parameter. The Proudman Oceanographic Laboratory Coastal Modelling System-Wave Model (POLCOMS-WAM) has been used to model combined tides, surges, waves and wave-current interaction in the Irish Sea on a 1.85 km grid. This period has been previously thoroughly studied, e.g. Jones and Davies [Jones, J.E., Davies, A.M., 1998. Storm surge computations for the Irish Sea using a three-dimensional numerical model including wave-current interaction. Continental Shelf Research 18(2), 201–251] and we build upon this previous work 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 from larger scale models to the Irish Sea model. 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 (1/9° by 1/6°) model extending beyond the continental shelf edge was run using the POLCOMS model for tide and surge. The model results were compared with tide gauge observations around the eastern Irish Sea. The model was tested with different wind-stress formulations including Smith and Banke [Smith, S.D., Banke, E.G., 1975. Variation of the surface drag coefficient with wind speed. Quarterly Journal of the Royal Meteorology Society, 101(429), 665–673] and Charnock [Charnock, H., 1955. Wind-stress on a water surface. Quarterly Journal of the Royal Meteorological Society, 81(350), 639–640]. In order to get a single parameterisation that works with wave-coupling, the wave-derived surface roughness length has been imposed in the surge model. One of the largest surge events that occurred at Liverpool in the last 10 years, in January 2007, has also been simulated for comparison to demonstrate the robust application of the coupled model.

Modelling the global coastal ocean

Shelf and coastal seas are regions of exceptionally high biological productivity, high rates of biogeochemical cycling and immense socio-economic importance. They are, however, poorly represented by the present generation of Earth system models, both in terms of resolution and process representation. Hence, these models cannot be used to elucidate the role of the coastal ocean in global biogeochemical cycles and the effects global change (both direct anthropogenic and climatic) are having on them. Here, we present a system for simulating all the coastal regions around the world (the Global Coastal Ocean Modelling System) in a systematic and practical fashion. It is based on automatically generating multiple nested model domains, using the Proudman Oceanographic Laboratory Coastal Ocean Modelling System coupled to the European Regional Seas Ecosystem Model. Preliminary results from the system are presented. These demonstrate the viability of the concept, and we discuss the prospects for using the system to explore key areas of global change in shelf seas, such as their role in the carbon cycle and climate change effects on fisheries.