Operational Ocean Modelling: a Critical Evaluation of Published Works

This thesis presents a subset of the author’s published works, and describes the impact his work has had on ocean forecasting systems. This impact can be broadly divided into two themes, the underpinning development of ocean forecasting models and the implementation, tuning and evaluation of those models to ensure they provide skilful products, with value to users. The systems described in this dissertation are recognised as amongst the best available, and are being used by commercial operators, military decisions makers and governmental organisations, as well as research users. They also form the basis on which future systems will be developed, meeting the challenges and addressing the priorities discussed in the thesis. The author expects to have a substantive impact on driving the research agenda in these areas over the coming years

Classifying and Identifying Negative Poisson's Ratio. An Examination of the Auxeticity in Zeolitic Materials

The aim of this thesis is to advance the understanding of auxeticity. This is achieved by developing a more accurate way to classify materials exhibiting the property, by carrying out high-throughput atomistic simulations of framework materials based on the SiO2 and GeO2 chemistries, and by exploring mechanistic models and possible correlations with directional density variations. At first this thesis outlines the development of a typographic system for negative Poisson's ratio. Materials are given classifications based on the degree to which auxetic behaviour is observed along specific axes of deformation and the frequency of occurrence of these axes. A systematic study is then performed on the elastic properties of zeolitic silicon dioxide and germanium dioxide structures. The typology is applied to these materials to better understand their auxetic behaviour. The JST framework is identified as isotropically auxetic, the first crystal to exhibit such general negative Poisson's ratios. An exploration into the effects of local density variations between parallel planes on Poisson's ratio is undertaken, but no clear correlation is found. Finally, software for systematically creating and evaluating two dimensional networks of triangles is produced. The geometrical analysis of these rotating structures predicts a high level of auxeticity and further work into three dimensional equivalents is recommended

A systematic typology for negative Poisson's ratio materials and the prediction of complete auxeticity in pure silica zeolite JST

© the Owner Societies 2015. Single crystals can commonly have negative Poisson's ratio in a few directions; however more generalised auxeticity is rarer. We propose a typology to distinguish auxetic materials. We characterise numerous single crystals and demonstrate that partial auxeticity occurs for around 37%. We find average auxeticity to be limited to α-cristobalite and no example of complete auxeticity. We simulate two hundreds pure silica zeolites with empirical potentials and quantum chemistry methods, and for the first time identify complete auxeticity in a zeolite network, JST

Passive remediation of mine waters from Parys Mountain (Wales): Laboratory column experiments

This study evaluates the effectiveness of dispersed alkaline substrate (DAS) technology to treat highly acidic and contaminated leachates from the oxidation of sulfide-rich mining wastes under wet temperate oceanic climate conditions. To address this issue, leachates from the abandoned mine at Parys Mountain (NW Wales) were passed through two sets of multistep columns filled with a mixture of a fine-grained alkaline reagent (i.e., limestone, MgO, or BaCO3) scattered in an inert matrix. The set of columns with the limestone-DAS plus MgO-DAS combination achieved a near total removal of Fe, Al, Zn, Cu, Mn, As, Co, Cd, and Ni. However, the elimination of SO4 was not significant (around 7%). The limestone-DAS plus BaCO3-DAS combination also achieved a high effectiveness for base metal/loids, allowing the removal of Fe, Al, Zn, Cu, As, and Cd with rates of nearly 100%. In addition, the system with the BaCO3-step had a higher effectiveness in eliminating SO4 (around 53%) than the combined treatment with the MgO-step. According to PHREEQC code calculations, the precipitation of oxyhydroxy-sulfates (i.e., schwertmannite and basaluminite) and carbonate (i.e., malachite, hydrozincite and calcite) phases may have controlled the solubility of pollutants during the passive treatment. The chemical compositions of the treated waters complied with the threshold values defined by irrigation standards, except for Mn in the BaCO3-DAS output.Funding for open access charge: Universidad de Huelva/CBUA

Evaluation of numerical models by FerryBox and fixed platform in situ data in the southern North Sea

For understanding and forecasting of hydrodynamics in coastal regions, numerical models have served as an important tool for many years. In order to assess the model performance, we compared simulations to observational data of water temperature and salinity. Observations were available from FerryBox transects in the southern North Sea and, additionally, from a fixed platform of the MARNET network. More detailed analyses have been made at three different stations, located off the English eastern coast, at the Oyster Ground and in the German Bight. FerryBoxes installed on ships of opportunity (SoO) provide high-frequency surface measurements along selected tracks on a regular basis. The results of two operational hydrodynamic models have been evaluated for two different time periods: BSHcmod v4 (January 2009 to April 2012) and FOAM AMM7 NEMO (April 2011 to April 2012). While they adequately simulate temperature, both models underestimate salinity, especially near the coast in the southern North Sea. Statistical errors differ between the two models and between the measured parameters. The root mean square error (RMSE) of water temperatures amounts to 0.72 °C (BSHcmod v4) and 0.44 °C (AMM7), while for salinity the performance of BSHcmod is slightly better (0.68 compared to 1.1). The study results reveal weaknesses in both models, in terms of variability, absolute levels and limited spatial resolution. Simulation of the transition zone between the coasts and the open sea is still a demanding task for operational modelling. Thus, FerryBox data, combined with other observations with differing temporal and spatial scales, can serve as an invaluable tool not only for model evaluation, but also for model optimization by assimilation of such high-frequency observations

The impact of a new high-resolution ocean model on the Met Office North-West European Shelf forecasting system

The North-West European Shelf ocean forecasting system has been providing oceanographic products for the European continental shelf seas for more than 15 years. In that time, several different configurations have been implemented, updating the model and the data assimilation components. The latest configuration to be put in operation, an eddy-resolving model at 1.5 km (AMM15), replaces the 7 km model (AMM7) that has been used for 8 years to deliver forecast products to the Copernicus Marine Environment Monitoring Service and its precursor projects. This has improved the ability to resolve the mesoscale variability in this area. An overview of this new system and its initial validation is provided in this paper, highlighting the differences with the previous version. Validation of the model with data assimilation is based on the results of 2 years (2016–2017) of trial experiments run with the low- and high-resolution systems in their operational configuration. The 1.5 km system has been validated against observations and the low-resolution system, trying to understand the impact of the high resolution on the quality of the products delivered to the users. Although the number of observations is a limiting factor, especially for the assessment of model variables like currents and salinity, the new system has been proven to be an improvement in resolving fine-scale structures and variability and provides more accurate information on the major physical variables, like temperature, salinity, and horizontal currents. AMM15 improvements are evident from the validation against high-resolution observations, available in some selected areas of the model domain. However, validation at the basin scale and using daily means penalized the high-resolution system and does not reflect its superior performance. This increment in resolution also improves the capabilities to provide marine information closer to the coast even if the coastal processes are not fully resolved by the model

The sensitivity of British weather to ocean tides

Tides in shelf seas greatly impact ocean mixing and temperature structure. Using a regional‐coupled ocean–atmosphere prediction system, at ocean coastal process and atmosphere convection permitting scales, we assess the influence of tides on British weather by comparing simulations with and without tides. In summer, when seasonal stratification is particularly sensitive to tides, the sea‐surface temperature is up to 6 K cooler in simulations with tidal mixing. Tides cool the air temperature over the sea by up to 3 K, and nearby land by up to 1.4 K. The mean air temperature across Great Britain land areas cools by 0.3 K with tides. Changes in near‐surface stability result in decreases in summer mean wind speeds over the ocean. A 6% reduction in summer precipitation is found with tides, consistent with cooler temperatures. This study has implications for climate projections since global‐coupled models typically do not include tides

Prospects for improving the representation of coastal and shelf seas in global ocean models

Accurately representing coastal and shelf seas in global ocean models represents one of the grand challenges of Earth system science. They are regions of immense societal importance through the goods and services they provide, hazards they pose and their role in global-scale processes and cycles, e.g. carbon fluxes and dense water formation. However, they are poorly represented in the current generation of global ocean models. In this contribution, we aim to briefly characterise the problem, and then to identify the important physical processes, and their scales, needed to address this issue in the context of the options available to resolve these scales globally and the evolving computational landscape. We find barotropic and topographic scales are well resolved by the current state-of-the-art model resolutions, e.g. nominal 1∕12°, and still reasonably well resolved at 1∕4°; here, the focus is on process representation. We identify tides, vertical coordinates, river inflows and mixing schemes as four areas where modelling approaches can readily be transferred from regional to global modelling with substantial benefit. In terms of finer-scale processes, we find that a 1∕12° global model resolves the first baroclinic Rossby radius for only  ∼ 8% of regions  < 500m deep, but this increases to  ∼ 70% for a 1∕72° model, so resolving scales globally requires substantially finer resolution than the current state of the art. We quantify the benefit of improved resolution and process representation using 1∕12° global- and basin-scale northern North Atlantic nucleus for a European model of the ocean (NEMO) simulations; the latter includes tides and a k-ε vertical mixing scheme. These are compared with global stratification observations and 19 models from CMIP5. In terms of correlation and basin-wide rms error, the high-resolution models outperform all these CMIP5 models. The model with tides shows improved seasonal cycles compared to the high-resolution model without tides. The benefits of resolution are particularly apparent in eastern boundary upwelling zones. To explore the balance between the size of a globally refined model and that of multiscale modelling options (e.g. finite element, finite volume or a two-way nesting approach), we consider a simple scale analysis and a conceptual grid refining approach. We put this analysis in the context of evolving computer systems, discussing model turnaround time, scalability and resource costs. Using a simple cost model compared to a reference configuration (taken to be a 1∕4° global model in 2011) and the increasing performance of the UK Research Councils' computer facility, we estimate an unstructured mesh multiscale approach, resolving process scales down to 1.5km, would use a comparable share of the computer resource by 2021, the two-way nested multiscale approach by 2022, and a 1∕72° global model by 2026. However, we also note that a 1∕12° global model would not have a comparable computational cost to a 1° global model in 2017 until 2027. Hence, we conclude that for computationally expensive models (e.g. for oceanographic research or operational oceanography), resolving scales to  ∼ 1.5km would be routinely practical in about a decade given substantial effort on numerical and computational development. For complex Earth system models, this extends to about 2 decades, suggesting the focus here needs to be on improved process parameterisation to meet these challenges

Evaluating the impact of atmospheric forcing and air–sea coupling on near-coastal regional ocean prediction

Atmospheric forcing applied as ocean model boundary conditions can have a critical impact on the quality of ocean forecasts. This paper assesses the sensitivity of an eddy-resolving (1.5 km resolution) regional ocean model of the north-west European Shelf (NWS) to the choice of atmospheric forcing and atmosphere–ocean coupling. The analysis is focused on a month-long simulation experiment for July 2014 and evaluation of simulated sea surface temperature (SST) in a shallow near-coastal region to the south-west of the UK (Celtic Sea and western English Channel). Observations of the ocean and atmosphere are used to evaluate model results, with a particular focus on the L4 ocean buoy from the Western Channel Observatory as a rare example of co-located data above and below the sea surface. The impacts of differences in the atmospheric forcing are illustrated by comparing results from an ocean model run in forcing mode using operational global-scale numerical weather prediction (NWP) data with an ocean model run forced by a convective-scale regional atmosphere model. The value of dynamically representing feedbacks between the atmosphere and ocean state is assessed via the use of these model components within a fully coupled ocean–wave–atmosphere system. Simulated SSTs show considerable sensitivity to atmospheric forcing and to the impact of model coupling in near-coastal areas. A warm ocean bias relative to in situ observations in the simulation forced by global-scale NWP (0.7 K in the model domain) is shown to be reduced (to 0.4 K) via the use of the 1.5 km resolution regional atmospheric forcing. When simulated in coupled mode, this bias is further reduced (by 0.2 K). Results demonstrate much greater variability of both the surface heat budget terms and the near-surface winds in the convective-scale atmosphere model data, as might be expected. Assessment of the surface heat budget and wind forcing over the ocean is challenging due to a scarcity of observations. However, it can be demonstrated that the wind speed over the ocean simulated by the convective-scale atmosphere did not agree as well with the limited number of observations as the global-scale NWP data did. Further partially coupled experiments are discussed to better understand why the degraded wind forcing does not detrimentally impact on SST results

Evaluating the impact of atmospheric forcing and air–sea coupling on near-coastal regional ocean prediction

Atmospheric forcing applied as ocean model boundary conditions can have a critical impact on the quality of ocean forecasts. This paper assesses the sensitivity of an eddy-resolving (1.5 km resolution) regional ocean model of the north-west European Shelf (NWS) to the choice of atmospheric forcing and atmosphere–ocean coupling. The analysis is focused on a month-long simulation experiment for July 2014 and evaluation of simulated sea surface temperature (SST) in a shallow near-coastal region to the south-west of the UK (Celtic Sea and western English Channel). Observations of the ocean and atmosphere are used to evaluate model results, with a particular focus on the L4 ocean buoy from the Western Channel Observatory as a rare example of co-located data above and below the sea surface. The impacts of differences in the atmospheric forcing are illustrated by comparing results from an ocean model run in forcing mode using operational global-scale numerical weather prediction (NWP) data with an ocean model run forced by a convective-scale regional atmosphere model. The value of dynamically representing feedbacks between the atmosphere and ocean state is assessed via the use of these model components within a fully coupled ocean–wave–atmosphere system. Simulated SSTs show considerable sensitivity to atmospheric forcing and to the impact of model coupling in near-coastal areas. A warm ocean bias relative to in situ observations in the simulation forced by global-scale NWP (0.7 K in the model domain) is shown to be reduced (to 0.4 K) via the use of the 1.5 km resolution regional atmospheric forcing. When simulated in coupled mode, this bias is further reduced (by 0.2 K). Results demonstrate much greater variability of both the surface heat budget terms and the near-surface winds in the convective-scale atmosphere model data, as might be expected. Assessment of the surface heat budget and wind forcing over the ocean is challenging due to a scarcity of observations. However, it can be demonstrated that the wind speed over the ocean simulated by the convective-scale atmosphere did not agree as well with the limited number of observations as the global-scale NWP data did. Further partially coupled experiments are discussed to better understand why the degraded wind forcing does not detrimentally impact on SST results