Modelling tidal energy converters in TELEMAC-3D

HydrodynamicsAbstrac

Space-based retrievals of air-sea gas transfer velocities using altimeters: Calibration for dimethyl sulfide

This study is the first to directly correlate gas transfer velocity, measured at sea using the eddy-correlation (EC) technique, and satellite altimeter backscattering. During eight research cruises in different parts of the world, gas transfer velocity of dimethyl sulfide (DMS) was measured. The sample times and locations were compared with overpass times and locations of remote sensing satellites carrying Ku-band altimeters: ERS-1, ERS-2, TOPEX, POSEIDON, GEOSAT Follow-On, JASON-1, JASON-2 and ENVISAT. The result was 179 pairs of gas transfer velocity measurements and backscattering coefficients. An inter-calibration of the different altimeters significantly reduced data scatter. The inter-calibrated data was best fitted to a quadratic relation between the inverse of the backscattering coefficients and the gas transfer velocity measurements. A gas transfer parameterization based on backscattering, corresponding with sea surface roughness, might be expected to perform better than wind speed-based parameterizations. Our results, however, did not show improvement compared to direct correlation of shipboard wind speeds. The relationship of gas transfer velocity to satellite-derived backscatter, or wind speed, is useful to provide retrieval algorithms. Gas transfer velocity (cm/hr), corrected to a Schmidt number of 660, is proportional to wind speed (m/s). The measured gas transfer velocity is controlled by both the individual water-side and air-side gas transfer velocities. We calculated the latter using a numerical scheme, to derive water-side gas transfer velocity. DMS is sufficiently soluble to neglect bubble-mediated gas transfer, thus, the DMS transfer velocities could be applied to estimate water-side gas transfer velocities through the unbroken surface of any other gas Key Points: - Show relations between altimeter data and field values of air-sea gas transfer - DMS gas transfer velocity can be used to estimate direct gas transfer of any gas - Direct gas transfer velocity (for Sc = 660) is roughly double 10 m wind spee

Sensitivity of ferry services to the Western Isles of Scotland to changes in wave and wind climate

PublishedJournal ArticleThis is the final version of the article. Available from AMS via the DOI in this record.The roughness of the seas is rarely mentioned as a major factor in the economic or social welfare of a region. In this study, the relationship between the ocean wave climate and the economy of the Western Isles of Scotland is examined. This sparsely populated region has a high dependency on marine activities, and ferry services provide vital links between communities. The seas in the region are among the roughest in the world during autumn and winter, however, making maintenance of a reliable ferry service both difficult and expensive. A deterioration in wave and wind climate either in response to natural variability or as a regional response to anthropogenic climate change is possible. Satellite altimetry and gale-frequency data are used to analyze the contemporary response of wave and wind climate to the North Atlantic Oscillation (NAO). The sensitivity of wave climate to the NAO extends to ferry routes that are only partially sheltered and are exposed to ocean waves; thus, the reliability of ferry services is sensitive to NAO. Any deterioration of the wave climate will result in a disproportionately large increase in ferry-service disruption. The impacts associated with an unusually large storm event that affected the region in January 2005 are briefly explored to provide an insight into vulnerability to future storm events. © 2013 American Meteorological Society.This research was largely supported by the Tyndall Centre for Climate Change Research project “Toward a vulnerability assessment for the UK coastline” (IT 1.15)

Asymmetric transfer of CO2 across a broken sea surface

Most estimates of the climatically-important transfer of atmospheric gases into, and out of, the ocean assume that the ocean surface is unbroken by breaking waves. However the trapping of bubbles of atmospheric gases in the ocean by breaking waves introduces an asymmetry in this flux. This asymmetry occurs as a bias towards injecting gas into the ocean where it dissolves, and against the evasion/exsolution of previously-dissolved gas coming out of solution from the oceans and eventually reaching the atmosphere. Here we use at-sea measurements and modelling of the bubble clouds beneath the ocean surface to show that the numbers of large bubbles found metres below the sea surface in high winds are sufficient to drive a large and asymmetric flux of carbon dioxide. Our results imply a much larger asymmetry for carbon dioxide than previously proposed. This asymmetry contradicts an assumption inherent in most existing estimates of ocean-atmosphere gas transfer. The geochemical and climate implications include an enhanced invasion of carbon dioxide into the stormy temperate and polar seas

Three very young HgMn stars in the Orion OB1 Association

We report the detection of three mercury-manganese stars in the Orion OB1 association. HD 37886 and BD-0 984 are in the approximately 1.7 million year old Orion OB1b. HD 37492 is in the approximately 4.6 million year old Orion OB1c. Orion OB1b is now the youngest cluster with known HgMn star members. This places an observational upper limit on the time scale needed to produce the chemical peculiarities seen in mercury-manganese stars, which should help in the search for the cause or causes of the peculiar abundances in HgMn and other chemically peculiar upper main sequence stars.Comment: 8 pages including 1 figure. To appear in Astrophysical Journal Letter

The wave and tidal resource of Scotland

As the marine renewable energy industry evolves, in parallel with an increase in the quantity of available data and improvements in validated numerical simulations, it is occasionally appropriate to re-assess the wave and tidal resource of a region. This is particularly true for Scotland - a leading nation that the international community monitors for developments in the marine renewable energy industry, and which has witnessed much progress in the sector over the last decade. With 7 leased wave and 17 leased tidal sites, Scotland is well poised to generate significant levels of electricity from its abundant natural marine resources. In this state-of-the-art review of Scotland's wave and tidal resource, we examine the theoretical and technical resource, and provide an overview of commercial progress. We also discuss issues that affect future development of the marine energy seascape in Scotland, applicable to other regions of the world, including the potential for developing lower energy sites, and grid connectivity

The links between marine plastic litter and the air-sea flux of greenhouse gases

Climate change and plastic pollution are two of the most pressing environmental challenges caused by human activity, and they are directly and indirectly linked. We focus on the relationship between marine plastic litter and the air-sea flux of greenhouse gases (GHGs). Marine plastic litter has the potential to both enhance and reduce oceanic GHG fluxes, but this depends on many factors that are not well understood. Different kinds of plastic behave quite differently in the sea, affecting air-sea gas exchange in different, largely unknown, ways. The mechanisms of air-sea exchange of GHGs have been extensively studied and if air-sea gas transfer coefficients and concentrations of the gas in water and air are known, calculating the resulting GHG fluxes is reasonably straightforward. However, relatively little is known about the consequences of marine plastic litter for gas transfer coefficients, concentrations, and fluxes. Here we evaluate the most important aspects controlling the exchange of GHGs between the sea and the atmosphere and how marine plastic litter could change these. The aim is to move towards improving air-sea GHG flux calculations in the presence of plastic litter and we have largely limited ourselves to identifying processes, rather than estimating relative importance

Activity-dependent silencing reveals functionally distinct itch-generating sensory neurons

The peripheral terminals of primary sensory neurons detect histamine and non-histamine itch-provoking ligands through molecularly distinct transduction mechanisms. It remains unclear, however, whether these distinct pruritogens activate the same or different afferent fibers. We utilized a strategy of reversibly silencing specific subsets of murine pruritogen-sensitive sensory axons by targeted delivery of a charged sodium-channel blocker and found that functional blockade of histamine itch did not affect the itch evoked by chloroquine or SLIGRL-NH2, and vice versa. Notably, blocking itch-generating fibers did not reduce pain-associated behavior. However, silencing TRPV1+ or TRPA1+ neurons allowed AITC or capsaicin respectively to evoke itch, implying that certain peripheral afferents may normally indirectly inhibit algogens from eliciting itch. These findings support the presence of functionally distinct sets of itch-generating neurons and suggest that targeted silencing of activated sensory fibers may represent a clinically useful anti-pruritic therapeutic approach for histaminergic and non-histaminergic pruritus

Satellites will address critical science priorities for quantifying ocean carbon

The ability to routinely quantify global carbon dioxide (CO2) absorption by the oceans has become crucial: it provides a powerful constraint for establishing global and regional carbon (C) budgets, and enables identification of the ecological impacts and risks of this uptake on the marine environment. Advances in understanding, technology, and international coordination have made it possible to measure CO2 absorption by the oceans to a greater degree of accuracy than is possible in terrestrial landscapes. These advances, combined with new satellite‐based Earth observation capabilities, increasing public availability of data, and cloud computing, provide important opportunities for addressing critical knowledge gaps. Furthermore, Earth observation in synergy with in‐situ monitoring can provide the large‐scale ocean monitoring that is necessary to support policies to protect ocean ecosystems at risk, and motivate societal shifts toward meeting C emissions targets; however, sustained effort will be needed