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Journal articleNissan H, Toumi R, 2016,
Regional modelling of rainfall erosivity: Sensitivity of soil erosion to aerosol emissions
, Quarterly Journal of the Royal Meteorological Society, Vol: 143, Pages: 265-277, ISSN: 1477-870XA rainfall erosivity scheme is implemented into the widely-used regional atmosphere-landmodel, WRF. Rainfall erosivity is parameterised from hourly precipitation and surface runoff in a high resolution (4 km) convection-permitting model. The scheme is used to examine thepotential effects of changes in atmospheric aerosol concentrations on soil erosion in a case study of northern India and the surrounding countries for the 2010 monsoon season, using a model which isolates the indirect effect on cloud microphysics only. This study offers a preliminary investigation into this emerging topic, but longer simulations would be needed to establish a robust signal.Summer precipitation is reduced in most areas and the monsoon circulation weakens for increases in cloud condensation nuclei concentrations. This can be attributed to localised cloud microphysical changes in the northeast of India, which induce a dynamic response opposing the monsoon circulation. The two regions of greatest decrease in erosion with increasing aerosolare in the Western Ghats and the Ganges Delta, both significant cropland areas. However, the effect is not uniform, with isolated local increases in soil erosion. These results suggest that, while efforts to reduce anthropogenic aerosol emissions may improve water availability for crops through enhanced rainfall, these benefits are likely to be tempered by an increase in soil erosion, though robust local changes were difficult to predict.
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Journal articleTrivedi A, Toumi R, 2016,
Mechanisms of bottom boundary fluxes in a numerical model of the Shetland shelf
, Ocean Dynamics, Vol: 67, Pages: 1-21, ISSN: 1616-7341Across-slope bottom boundary layer (BBL) fluxes on the shelf-edge connectthis region to deeper waters. Two proposed ways in which across-slope BBLfluxes can occur, in regions that have a slope current aligned to the bathymetry, are:the frictional veering of bottom currents termed the ‘Ekman drain’; and through localwind-forced downwelling (wind-driven surface Ekman flow with an associated bottomflow). We investigate the variability, magnitude and spatial scale of BBL fluxeson the Shetland shelf, which has a prominent slope current, using a high-resolution(∼ 2 km) configuration of the MITgcm model. Fluxes are analysed in the BBL atthe shelf break near the 200 m isobath and are found to have a seasonal variabilitywith high/low volume transport in winter/summer respectively. By using a multivariateregression approach, we find that the locally wind-driven Ekman transport playsno explicit role in explaining daily bottom fluxes. We can better explain the variabilityof the across-slope BBL flux as a linear function of the speed and across-slopecomponent of the interior flow, corresponding to an Ekman plus mean-flow flux. Weestimate that the mean-flow is a greater contributor than the Ekman flux to the BBLflux. The spatial heterogeneity of the BBL fluxes can be attributed to the mean-flow,which has a much shorter decorrelation length compared to the Ekman flux. We concludethat both the speed and direction of the interior current determines the dailyBBL flux. The wind does not explicitly contribute through local downwelling, butmay influence the interior current and therefore implicitly the BBL fluxes on longertimescales.
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Journal articleBruneau N, Toumi R, 2016,
A fully-coupled atmosphere-ocean-wave model of the Caspian Sea
, Ocean Modelling, Vol: 107, Pages: 97-111, ISSN: 1463-5011Located in the mid-latitudes, the Caspian Sea is the largest enclosed basin in the world. A fully-coupled atmosphere-ocean-wave model of the Caspian Sea at high resolution (8 km) for a period of three years is presented. After validating each component of the modelling platform, the wave state of the Caspian Sea is studied. Results show very different wave regimes between the three different basins, a strong seasonality and an almost swell-free state. It is shown here that waves modify the horizontal eddy viscosity and vertical heat diffusion. However, due to a reasonably weak annual wave state, these effects are restricted to the upper-ocean layer (< 30 m) except during the most severe events (100 m).Three main experiments are conducted: 1) the ROMS ocean model forced by atmospheric reanalysis (CFSR), 2) ROMS coupled with the atmospheric model WRF and 3) the impact of wave-induced processes. The seasonality of the Caspian Sea is accurately captured in each experiment which highlights a rapid warming of the sea surface temperature (SST) in spring while the mixed layer depths (MLD) become very rapidly shallow (shifting from over 100 m to 15 m in two months). Contrarily, a gentle cooling of the SST accompanied with a deepening of the MLD is modelled during autumn and winter. The results also show a significant improvement of the model skill in the representation of the dynamics when ROMS is coupled to WRF.Finally, as ocean surface waves imply feedback at the interface atmosphere-ocean through the transfer of momentum, mass and heat, we investigate their potential effects on the Caspian Sea dynamics. Results are mixed and show a reasonably weak impact of wave-induced processes. While waves have a negligible effect during the winter as wave-induced mixing is confined to the MLD, the summer global SST are less accurately modelled due to the enhancement of mixing in shallow MLDs. However the SST bias, temperature at a subsurface location are improved.
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Journal articleWang S, Toumi R, 2016,
On the relationship between hurricane cost and the integrated wind profile
, Environmental Research Letters, Vol: 11, ISSN: 1748-9326It is challenging to identify metrics that best capture hurricane destructive potential and costs. Although it has been found that the sea surface temperature and vertical wind shear can both make considerable changes to the hurricane destructive potential metrics, it is still unknown which plays a more important role. Here we present a new method to reconstruct the historical wind structure of hurricanes that allows us, for the first time, to calculate the correlation of damage with integrated power dissipation and integrated kinetic energy of all hurricanes at landfall since 1988. We find that those metrics, which include the horizontal wind structure, rather than just maximum intensity, are much better correlated with the hurricane cost. The vertical wind shear over the main development region of hurricanes plays a more dominant role than the sea surface temperature in controlling these metrics and therefore also ultimately the cost of hurricanes.
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Journal articleWang S, Toumi R, 2016,
On the relationship between hurricane cost and the integrated wind profile
, Environmental Research Letters, Vol: 11, ISSN: 1748-9326It is challenging to identify metrics that best capture hurricane destructive potential and costs. Although it has been found that the sea surface temperature and vertical wind shear can both make considerable changes to the hurricane destructive potential metrics, it is still unknown which plays a more important role. Here we present a new method to reconstruct the historical wind structure of hurricanes that allows us, for the first time, to calculate the correlation of damage with integrated power dissipation and integrated kinetic energy of all hurricanes at landfall since 1988. We find that those metrics, which include the horizontal wind structure, rather than just maximum intensity, are much better correlated with the hurricane cost. The vertical wind shear over the main development region of hurricanes plays a more dominant role than the sea surface temperature in controlling these metrics and therefore also ultimately the cost of hurricanes.
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Journal articleChang S, Cao X, Zou Z, et al., 2016,
Microbubble Swarms in a Full-Scale Water Model Tundish
, Metallurgical and Materials Transactions B Process Metallurgy and Materials Processing Science, Vol: 47, Pages: 2732-2743, ISSN: 1073-5615Water modeling, using microbubble swarms, was performed in a full-scale, four-strand, delta-shaped tundish, located at the McGill Metals Processing Centre (MMPC). The objective of the study was to investigate the effectiveness of microbubbles in removing inclusions smaller than 50 μm, applying the principles and conditions previously researched using a smaller scale arrangement. Air was injected into a full-scale model of a ladle shroud (the connecting tube through which liquid steel flows into the tundish below). The model ladle shroud was fitted with twelve, laser-drilled orifices, so as to create microbubbles. The bubbles generated using different gas injection protocols were recorded using a high-speed camera, and the bubble images were postprocessed using the commercial software, ImageJ. With this newly designed ladle shroud, bubble sizes could be reduced dramatically, to as small as a 675 µm average diameter. A three-dimensional, CFD model simulation was developed, using parameters obtained from the corresponding water model experiments, in order to predict the behavior of these microbubbles within the tundish and their potential influence on flow patterns and inclusion float-out capability.
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Journal articleOluleye G, Smith R, 2016,
A mixed integer linear programming model for integrating thermodynamic cycles for waste heat exploitation in process sites
, Applied Energy, Vol: 178, Pages: 434-453, ISSN: 0306-2619© 2016 Elsevier Ltd Thermodynamic cycles such as organic Rankine cycles, absorption chillers, absorption heat pumps, absorption heat transformers, and mechanical heat pumps are able to utilize wasted thermal energy in process sites for the generation of electrical power, chilling and heat at a higher temperature. In this work, a novel systematic framework is presented for optimal integration of these technologies in process sites. The framework is also used to assess the best design approach for integrating waste heat recovery technologies in process sites, i.e. stand-alone integration or a systems-oriented integration. The developed framework allows for: (1) selection of one or more waste heat sources (taking into account the temperatures and thermal energy content), (2) selection of one or more technology options and working fluids, (3) selection of end-uses of recovered energy, (4) exploitation of interactions with the existing site utility system and (5) the potential for heat recovery via heat exchange is also explored. The methodology is applied to an industrial case study. Results indicate a systems-oriented design approach reduces waste heat by 24%; fuel consumption by 54% and CO2 emissions by 53% with a 2 year payback, and stand-alone design approach reduces waste heat by 12%; fuel consumption by 29% and CO2 emissions by 20.5% with a 4 year payback. Therefore, benefits from waste heat utilization increase when interactions between the existing site utility system and the waste heat recovery technologies are explored simultaneously. The case study also shows that the novel methodology can select and design optimal solutions for waste heat exploitation which are technically, economically and environmentally feasible from a range of technology options, heat sources and end-uses of recovered energy.
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Journal articleOluleye G, Johnson M, Smith R, 2016,
Process integration of waste heat upgrading technologies
, Process Safety and Environmental Protection, Vol: 103, Pages: 315-333, ISSN: 0957-5820© 2016 The Institution of Chemical Engineers Technologies such as mechanical heat pumps, absorption heat pumps and absorption heat transformers allow low-temperature waste heat to be upgraded to higher temperatures. This work develops a comprehensive Mixed Integer Linear Program (MILP) to integrate such technologies into existing process sites. The framework considers interactions with the associated cogeneration system (in order to exploit end-uses of upgraded heat within the system and determine their true value), temperature and quantity of waste heat sources and of sinks for the heat upgraded as well as process economics and the potential to reduce carbon dioxide (CO2) emissions. The methodology is applied to an industrially relevant case study. Integration of heat upgrading technologies has potential to reduce total costs by 23%. Sensitivity analysis is also performed to illustrate the effect of changing capital costs and energy prices on the results, and demonstrate the model functionality.
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Journal articleToumi R, wong B, 2016,
Effect of extreme ocean precipitation on sea surface elevation and storm surges
, Quarterly Journal of the Royal Meteorological Society, Vol: 142, Pages: 2541-2550, ISSN: 1477-870XOcean models that neglect mass and momentum contributions from precipitation can have asystematic bias in sea surface height (SSH). Here, a new rainfall scheme is introduced intothe Regional Ocean Modelling System (ROMS) to incorporate the effects of precipitationmass. When precipitation is added to the sea surface, it spreads out via surface gravity wavesthat increase in propagation speed with increasing water depth. Over several days, the SSHincrease due to the precipitation mass added created a geostrophic adjustment, generatinganti-cyclonic geostrophic currents around the SSH increase. The transfer of momentum fromprecipitation to the sea surface, or rain stress, can also be important. In the case study of areal tropical cyclone, Monica passing North Australia, the effect of incorporatingprecipitation mass is compared with other processes affecting the storm surge: surface wind,inverse barometer effect and rain stress. The maximum SSH response is 170.6 cm for thewind effect, 61.5 cm for the inverse barometer effect, 7.5 cm for the effect of rain stress and6.4 cm for the effect of rain mass. Each process has been shown to have different spatialinfluences. The effect of rain mass has a strong remote influence compared to the inversebarometer effect and the effect of rain stress. This is particularly seen in semi-enclosed bays.
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Journal articlePhibbs S, Toumi R, 2016,
The dependence of precipitation and its footprint on atmospheric temperature in idealized extratropical cyclones
, Journal of Geophysical Research: Atmospheres, Vol: 121, Pages: 8743-8754, ISSN: 2169-8996Flood hazard is a function of the magnitude and spatial pattern of precipitation accumulation.The sensitivity of precipitation to atmospheric temperature is investigated for idealized extratropicalcyclones, enabling us to examine the footprint of extreme precipitation (surface area where accumulatedprecipitation exceeds high thresholds) and the accumulation in different-sized catchment areas. Themean precipitation increases with temperature, with the mean increase at 5.40%/∘C. The 99.9th percentileof accumulated precipitation increases at 12.7%/∘C for 1 h and 9.38%/∘C for 24 h, both greater thanClausius-Clapeyron scaling. The footprint of extreme precipitation grows considerably with temperature,with the relative increase generally greater for longer durations. The sensitivity of the footprint of extremeprecipitation is generally super Clausius-Clapeyron. The surface area of all precipitation shrinks withincreasing temperature. Greater relative changes in the number of catchment areas exceeding extremetotal precipitation are found when the domain is divided into larger rather than smaller catchment areas.This indicates that fluvial flooding may increase faster than pluvial flooding from extratropical cyclones in awarming world. When the catchment areas are ranked in order of total precipitation, the 99.9th percentile isfound to increase slightly above Clausius-Clapeyron expectations for all of the catchment sizes, from 9 km2to 22,500 km2. This is surprising for larger catchment areas given the change in mean precipitation. Wepropose that this is due to spatially concentrated changes in extreme precipitation in the occluded front
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Conference paperRhodes A, van Diemen R, 2016,
Has the Low Carbon Network Fund been successful at stimulating innovation in the electricity networks?
, British Instutite of Energy Economics 2016: Innovation and Disruption: The Energy Sector in TransitionThe physical basis of today’s electricity networks are based on engineering design principles whichhave not changed substantially since World War 2. This has led to a stable, secure but intrinsicallyconservative electricity network system, characterised by small, incremental changes andtechnological advances. However, two major drivers are currently pushing a period of substantialinnovation and change in the networks. The first of these is the need to incorporate increasingquantities of variable renewable generation at distribution level, as well as to prepare for increasinglevels of electrification in heating and transport. The second comprises the new opportunities arisingfrom the incorporation of ICT technology into the networks, including smart metering, smartappliances, demand-side participation and the development of new business models and serviceswhich facilitate active consumer engagement.These drivers challenge the notion of an electricity grid being a simple unidirectional series of wiresand transformers and make the case for a ‘smart grid’, in which information and communicationtechnologies (ICT) are integrated directly into the electricity networks. These advances have thepotential to transform the way customers and supply companies interact with electricity, and providesignificant new commercial opportunities for communications, monitoring, control and dataaggregation technologies throughout the electricity system from generation through to the consumer.New network and smart grid technologies are a major focus in the UK’s low carbon innovationstrategy, with substantial public funding (£81 million p.a) provided through the Ofgem-administeredLow Carbon Network Fund (LCNF) and its successor the Network Innovation Competition (NIC).These are novel programmes, both in the UK and elsewhere due to their structure, which involvesconsortia led by network operating companies bidding for public funds. The LCNF has recentlycompleted i
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Journal articleToumi R, Wong B, 2016,
Model study of the asymmetry in tropical cyclone-induced positive and negative surges
, Atmospheric Science Letters, Vol: 17, Pages: 334-338, ISSN: 1530-261XStorm surges pose significant threats to coastal communities, yet negative surges are not aswell understood as positive surges. In this study, idealized experiments of a tropical cycloneforcing a 3D ocean model are conducted to investigate the asymmetry of positive andnegative surges. Negative surges are larger in magnitude and extend further across thecoastline than positive surges. While positive surges are driven by wind blowing onshore,negative surges are largely dominated by alongshore winds, with horizontal divergence as themain mechanism. This asymmetry also increases with decreasing depth and increasinglatitude.
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Journal articleOluleye G, Smith R, Jobson M, 2016,
Modelling and screening heat pump options for the exploitation of low grade waste heat in process sites
, Applied Energy, Vol: 169, Pages: 267-286, ISSN: 0306-2619© 2016 Elsevier Ltd. The need for high efficiency energy systems is of vital importance, due to depleting reserves of fossil fuels and increasing environmental problems. Industrial operations commonly feature the problem of rejecting large quantities of low-grade waste heat to the environment. The aim of this work is to develop methods for the conceptual screening and incorporation of low-temperature heat upgrading technologies in process sites.The screening process involves determination of the best technology to upgrade waste heat in process sites, and the combination of waste heat source and sink temperatures for a technology. Novel simplified models of mechanical heat pumps, absorption heat pumps and absorption heat transformers are proposed to support this analysis. These models predict the ratio of the real performance to the ideal performance in a more accurate way, than previous simplified models, taking into account the effect of changing operating temperatures, working fluids non-ideal behaviour and the system component inefficiencies.A novel systems-oriented criterion is also proposed for conceptual screening and selection of heat pumps in process sites. The criterion (i.e. the primary fuel recovery ratio) measures the savings in primary fuel from heat upgraded, taking into account power required to drive mechanical heat pumps and missed opportunities for steam generation when absorption systems are used.A graphical based methodology is also developed for applying the PRR in process sites and applied to a medium scale petroleum refinery. Results show that applying the PRR yields 9.2% additional savings in primary fuel compared to using the coefficient of performance to screen and incorporate heat pumps.
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Journal articlePoulain V, Bekki S, Marchand M, et al., 2016,
Evaluation of the inter-annual variability of stratospheric chemical composition in chemistry-climate models using ground-based multi species time series
, Journal of Atmospheric and Solar-Terrestrial Physics, Vol: 145, Pages: 61-84, ISSN: 1364-6826The variability of stratospheric chemical composition occurs on a broad spectrum of timescales, ranging from day to decades. A large part of the variability appears to be driven by external forcings such as volcanic aerosols, solar activity, halogen loading, levels of greenhouse gases (GHG), and modes of climate variability (quasi-biennial oscillation (QBO), El Niño-Southern Oscillation (ENSO)). We estimate the contributions of different external forcings to the interannual variability of stratospheric chemical composition and evaluate how well 3-D chemistry-climate models (CCMs) can reproduce the observed response-forcing relationships. We carry out multivariate regression analyses on long time series of observed and simulated time series of several traces gases in order to estimate the contributions of individual forcings and unforced variability to their internannual variability. The observations are typically decadal time series of ground-based data from the international Network for the Detection of Atmospheric Composition Change (NDACC) and the CCM simulations are taken from the CCMVal-2 REF-B1 simulations database. The chemical species considered are column O3, HCl, NO2, and N2O. We check the consistency between observations and model simulations in terms of the forced and internal components of the total interannual variability (externally forced variability and internal variability) and identify the driving factors in the interannual variations of stratospheric chemical composition over NDACC measurement sites. Overall, there is a reasonably good agreement between regression results from models and observations regarding the externally forced interannual variability. A much larger fraction of the observed and modelled interannual variability is explained by external forcings in the tropics than in the extratropics, notably in polar regions. CCMs are able to reproduce the amplitudes of responses in chemical composition to specific external forcings. H
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Journal articleGiordano L, Han B, Risch M, et al., 2016,
pH dependence of OER activity of oxides: Current and future perspectives
, CATALYSIS TODAY, Vol: 262, Pages: 2-10, ISSN: 0920-5861- Cite
- Citations: 412
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Conference paperRhodes A, 2016,
What lessons for innovation can be learnt from the Low Carbon Networks Fund?
, EI Energy Systems Conference 2016 -
Journal articleOluleye G, Jobson M, Smith R, et al., 2016,
Evaluating the potential of process sites for waste heat recovery
, Applied Energy, Vol: 161, Pages: 627-646, ISSN: 0306-2619As a result of depleting reserves of fossil fuels, conventional energy sources are becoming less available. In spite of this, energy is still being wasted, especially in the form of heat. The energy efficiency of process sites (defined as useful energy output per unit of energy input) may be increased through waste heat utilisation, thereby resulting in primary energy savings.In this work, waste heat is defined and a methodology developed to identify the potential for waste heat recovery in process sites; considering the temperature and quantity of waste heat sources from the site processes and the site utility system (including fired heaters and, the cogeneration, cooling and refrigeration systems). The concept of the energy efficiency of a site is introduced – the fraction of the energy inputs that is converted into useful energy (heat or power or cooling) to support the methodology. Furthermore, simplified mathematical models of waste heat recovery technologies using heat as primary energy source, including organic Rankine cycles (using both pure and mixed organics as working fluids), absorption chillers and absorption heat pumps are developed to support the methodology. These models are applied to assess the potential for recovery of useful energy from waste heat.The methodology is illustrated for an existing process site using a case study of a petroleum refinery. The energy efficiency of the site increases by 10% as a result of waste heat recovery. If there is an infinite demand for recovered energy (i.e. all the recoverable waste heat sources are exploited), the site energy efficiency could increase by 33%. The methodology also shows that combining technologies into a system creates greater potential to exploit the available waste heat in process sites.
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Journal articleChang S, Cao X, Hsin CH, et al., 2016,
Removal of inclusions using micro-bubble swarms in a four-strand, full-scale, water model tundish
, ISIJ International, Vol: 56, Pages: 1188-1197, ISSN: 0915-1559Water model experiments were performed in a full-scale, delta-shaped water model tundish, in order to study the removal of inclusions by micro-bubbles. Micro-bubbles were generated using a specially designed ladle shroud with twelve laser-drilled orifices. Gas flow rates, injection positions and multi-port injection were all taken into consideration to create different bubble conditions. Bubbles were recorded using a high speed camera and post-processed with commercial software, Image J. Hollow glass borosilicate microspheres, smaller than 100 μm, were used to simulate inclusions, and detected, in-situ, using a new generation of the Aqueous Particle Sensor, APS III. The results revealed that the effect of microbubbles on inclusion removal depends greatly on the gas injection protocols used. The optimum gas flow rate was an intermediate value, which indicates a minimum particle number density, n<inf>p</inf>, of about 7.85/ml. This results from the counter-balancing effects of bubble sizes against the total number of bubbles. The highest inclusion removal rate was 80%, when gas was injected through the four ports located closest to the slide gate, at a gas flow rate of 0.2 L/min.
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Conference paperCao XK, Chang S, Hsin CH, et al., 2016,
An aqueous particle sensor (APS) for micro-bubble detection in a four-strand, full-scale, water model tundish
Due to the increasingly stringent cleanliness requirements for final steel products, there has been a growing interest in the possible use of micro-bubbles for the removal of inclusions with diameters smaller than ~50µm, present within the steel passing through a steelmaking tundish. However, several technological barriers have prevented the adoption of this technique in industry. These are related to a) the generation of micro-bubbles in liquid steel, b) the measurement of bubble size distributions, and c) the optimization of bubble injection conditions to create micro-bubbles. In the present study, a novel Aqueous Particle Sensor (APS) system was developed for the in-situ, on-line, detection of micro-bubbles in water, generated by a newly designed full-scale ladle shroud, located at McGill Metal Processing Centre (MMPC). Measurement results from the sensor were validated against bubble size data collected through a high speed camera and post-processed through the commercial software, Image J. Control variables and orthogonal experiments were designed to assess the dependence of average micro-bubble sizes and bubble size distributions on key experimental parameters. Those chosen were the air inlet flowrate, the distance of the gas injection port from the slide gate, and the number of injection ports used. The investigation demonstrated that the APS system can be successfully adapted to detect micro-bubbles up to ~800 micron diameters. Using this novel sensor, it was shown that multi-port injection using low air inlet flowrates, closer to the slide gate, were useful in forming small micro-bubbles within the flow through the ladle shroud. The results from the APS system were compared and validated against data resulting from an optical technique.
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Journal articleOluleye G, Vasquez L, Smith R, et al., 2016,
A multi-period Mixed Integer Linear Program for design of residential distributed energy centres with thermal demand data discretisation
, Sustainable Production and Consumption, Vol: 5, Pages: 16-28, ISSN: 2352-5509Distributed Energy (DE) has gained significant interest in recent years as a way to maximise the efficient use of fuel for the production of electricity and heat. The concept of DE is to produce energy close to the end users. The increased fuel efficiency allows a significant reduction in carbon dioxide (CO2) emissions. In this paper, the sizes and the number of heat and power supply units are determined by an optimisation procedure that minimises the total annual cost. A Mixed Integer Linear Programming (MILP) model is developed to design new DE centres from a portfolio of possible technologies to service the thermal and power demand profiles of a geographic region. In this model, the partial load required for the combined heat and power (CHP) units and the equipment operating schedule in time intervals are selected to meet the demand data. The approach requires that energy demand be represented by discrete time bands to model the variations according to the time of day, day of the week and season of the year. Selection of inappropriate time bands can lead to misleading results. In this paper a systematic procedure for selecting time bands is proposed. The optimisation model is demonstrated in a case study. Results indicate that 70%–86% reduction in CO2 emissions is possible relative to individual building heating systems. Including thermal storage in the design of distributed energy centres achieves 54% reduction in CO2 emissions compared to design without thermal storage, since fossil fuelled units are not operated continuously.
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ReportMacLean K, Gross R, Hannon M, et al., 2015,
Energy system crossroads - time for decisions:UK 2030 low carbon scenarios and pathways - key decision points for a decarbonised energy system
, ICEPT/WP/2015/019 -
Journal articleOluleye G, Jobson M, Smith R, 2015,
A hierarchical approach for evaluating and selecting waste heat utilization opportunities
, Energy, Vol: 90, Pages: 5-23, ISSN: 0360-5442This paper presents a ranking criterion for evaluating opportunities that utilize recovered energy from the available waste heat in process sites. The ranking criterion takes into account the energy performance of waste heat recovery technologies associated with each opportunity, their potential to reduce greenhouse gas emissions (namely CO<inf>2</inf>) and the economics (costs and benefits). Mathematical modelling of the opportunities using the ranking criterion is developed to allow for systematic evaluation of opportunities, for example within an optimization framework. A methodology using the ranking criterion to design site waste heat recovery systems is also proposed. The methodology is applied to a case study of a petroleum refinery. Hierarchy and performance of waste heat utilization opportunities depends on the temperature of the heat available, amongst other factors. The site operating cost and CO<inf>2</inf> emissions reduce by 26% and 18% respectively when opportunities to use the recovered energy from waste heat within and outside the process site boundaries are explored. Sensitivity of the ranking to energy prices is studied, to explore the outlook for waste heat utilization in the future. The methodology can be applied to the process industries and other facilities producing waste heat.
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Journal articleBroadbridge MB, Toumi R, 2015,
The deep circulation of the Faroe-Shetland Channel:Opposing flows and topographic eddies
, Journal of Geophysical Research: Oceans, Vol: 120, Pages: 5983-5996, ISSN: 2169-9291New insights into the deep circulation of the Faroe-Shetland channel are gained from a highresolutionregional ocean model. The simulation shows a more complex structure of the deep flow fieldthan previously thought: a flow reversal of the deep and intermediate waters to the northeast on the Faroeseflank of the channel and persistent topographic eddies that force the deep currents into a gyre-likestructure. This flow reversal opposes the previously accepted understanding of a purely southwestwarddeep flow but is in agreement with velocity measurements. The southwestward transport of the overflowwaters is found to be facilitated almost exclusively by a strong and narrow current on the Shetland side ofthe channel. Float release experiments show that up to 38% of the overflow water takes longer than apurely southwestward flow regime suggests and up to 13% takes twice as long. From the release of tracers,a substantial amount of lateral mixing is evident within the channel, predominantly facilitated by the topographiceddies.
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Journal articleTamura-Wicks H, Toumi R, Budgell WP, 2015,
Sensitivity of Caspian sea-ice to air temperature
, Quarterly Journal of the Royal Meteorological Society, Vol: 141, Pages: 3088-3096, ISSN: 1477-870XCaspian sea ice concentration from satellite passive microwave data and surface daily air temperatures are analysed from 1978 to 2009. Relationships between mean winter air temperatures, cumulative freezing degree days (CFDD) and the sum of daily ice area (cumulative ice area) are found. These show that mean monthly air temperature of less than 5.5–9.5 °C, and a minimum CFDD of 3.6 ± 11.2 °C, are required for ice formation in the northern Caspian. Examination of climate projections from multi-model ensembles of monthly mean air temperatures suggest that the northern Caspian may be largely ice-free by 2100 for the highest emission scenario. An ocean–ice–atmosphere model of the Caspian shows weak sensitivities of the minimum CFDD to varied sea ice albedo and ice compressive strength. Sea level decline is found to reduce the minimum CFDD as well as promote the formation of higher concentration or ‘closed ice’.
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Journal articleWang S, Toumi R, Czaja A, et al., 2015,
An analytic model of tropical cyclone wind profiles
, Quarterly Journal of the Royal Meteorological Society, Vol: 141, Pages: 3018-3029, ISSN: 1477-870XA physically based analytic model (λ model) is presented to describe the wind profile of tropical cyclones in terms of the pressure deficit and a single shape parameter (λ). To test the λ model, an idealized full-physics numerical model is employed to provide wind-profile samples and also to show the influence of environmental temperature and the properties of initial vortices on tropical cyclone size. It is found that the λ model provides an accurate fit of the azimuthal wind profile at the top of the boundary layer. In the simulations, tropical cyclone size is sensitive to sea-surface temperature, upper tropospheric temperature and initial vortex structure. The numerical model confirms the assumed Gaussian distribution with width λ of the moist entropy in the boundary layer. A linear relationship between model cyclone size and inline image is found, in agreement with the λ model. The λ model predicts a weak relationship between tropical cyclone size and intensity, as is observed. In addition, the λ model suggests that change in tropical cyclone size should be closely related to angular momentum transport near the boundary layer, as has been found in observations. The good agreement of the λ model with the numerical model shows that the λ model could be a reasonable alternative for characterizing the wind structure of tropical cyclones with only one scaling parameter.
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Journal articleLefauve A, Muller C, Melet A, 2015,
A three-dimensional map of tidal dissipation over abyssal hills
, JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, Vol: 120, Pages: 4760-4777, ISSN: 2169-9275- Cite
- Citations: 26
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Journal articleBossay S, Bekki S, Marchand M, et al., 2015,
Sensitivity of tropical stratospheric ozone to rotational UV variations estimated from UARS and Aura MLS observations during the declining phases of solar cycles 22 and 23
, Journal of Atmospheric and Solar-Terrestrial Physics, Vol: 130-131, Pages: 96-111, ISSN: 1364-6826The correlation between tropical stratospheric ozone and UV radiation on solar rotational time scales is investigated using daily satellite ozone observations and reconstructed solar spectra. We consider two 3-year periods falling within the descending phases of two 11-year solar cycles 22 (1991-1994) and 23 (2004-2007). The UV rotational cycle is highly irregular and even disappears for half a year during cycle 23. For the 1991-1994 period, ozone and 205 nm UV flux are found to be correlated between about 10 and 1 hPa with a maximum of 0.29 at ~5 hPa; ozone sensitivity (percentage change in ozone for 1 percent change in UV) peaks at ~0.4. Correlation during cycle 23 is weaker with a peak ozone sensitivity of 0.2. The correlation is found to vary widely, not only with altitude, but also from one year to the next with a rotational signal in ozone appearing almost intermittent. Unexpectedly, the correlation is not found to bear any relation with the solar rotational forcing. For instance, solar rotational fluctuations are by far the strongest during 1991-1992 whereas the correlation peaks at the end of 1993, a rotationally quiescent period. When calculated over sliding intervals of 1-year, the sensitivity is found to vary very strongly within both 3-year periods; it is almost negligible over the entire vertical profile during some 1-year intervals or reaches close to 1 around 2-5 mb for other intervals. Other sources of variability, presumably of dynamical origin, operate on the rotational spectral range and determine to a large extent the estimated solar rotational signal. Even considering 3 years of observations (corresponding to about 40 solar cycles), the extraction of the rotational solar signal does not appear to be robust during declining phases of 11-year solar cycles. As observational studies cover at best three 11-year solar cycles, it must be challenging to produce a reliable estimation of the 11-year solar cycle signal in stratospheric ozone, especially in
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Conference paperOluleye OO, Jobson M, Smith R, 2015,
Optimisation-based design of site waste heat recovery systems
, ECOS 2015 - 28th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems -
Journal articleNewinger C, Toumi R, 2015,
Potential impact of the colored Amazon and Orinoco plume on tropical cyclone intensity
, Journal of Geophysical Research: Oceans, Vol: 120, Pages: 1296-1317, ISSN: 2169-9275 -
Journal articleHardwick SR, Toumi R, Pfeifer M, et al., 2015,
The relationship between leaf area index and microclimate in tropical forest and oil palm plantation: Forest disturbance drives changes in microclimate
, Agricultural and Forest Meteorology, Vol: 201, Pages: 187-195, ISSN: 0168-1923Land use change is a major threat to biodiversity. One mechanism by which land use change influences biodiversity and ecological processes is through changes in the local climate. Here, the relationships between leaf area index and five climate variables – air temperature, relative humidity, vapour pressure deficit, specific humidity and soil temperature – are investigated across a range of land use types in Borneo, including primary tropical forest, logged forest and oil palm plantation. Strong correlations with the leaf area index are found for the mean daily maximum air and soil temperatures, the mean daily maximum vapour pressure deficit and the mean daily minimum relative humidity. Air beneath canopies with high leaf area index is cooler and has higher relative humidity during the day. Forest microclimate is also found to be less variable for sites with higher leaf area indices. Primary forest is found to be up to 2.5 °C cooler than logged forest and up to 6.5 °C cooler than oil palm plantations. Our results indicate that leaf area index is a useful parameter for predicting the effects of vegetation upon microclimate, which could be used to make small scale climate predictions based on remotely sensed data.
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