Ocean Dynamics - In this study, we diagnose the time variability and vertical structure of the high- and low-frequency motions on the Mississippi-Alabama Shelf as observed with a bottom-mounted... 相似文献
This paper provides a summary of a number of indoor air quality studies reporting concentrations of volatile organic compounds (VOCs) in indoor air samples collected from residential properties in North America and provides average values for certain statistics (percentiles, detection frequency, maximum). This compilation includes several VOCs that are commonly assessed in studies of subsurface vapor intrusion to indoor air, but may also be attributable to consumer products, building materials, or even outdoor air (ambient) sources, specifically benzene, carbon tetrachloride, chloroform, 1,1-dichloroethane, 1,1-dichloroethene, 1,2-dichloroethane, cis and trans-1,2-dichloroethene, ethylbenzene, methyl tert-butyl ether, methylene chloride, tetrachloroethene, trichloroethene, toluene, trichloro-1,2,2-trifluoroethane, 1,1,1-trichloroethane, vinyl chloride, and meta, para, and ortho-xylene. In studies spanning 1990 through 2005, eleven of these compounds were detected in more than 50% of samples collected, and for several compounds (benzene, carbon tetrachloride, chloroform, ethylbenzene, and tetrachloroethene) the lower and upper quintiles of the indoor air concentrations are within the range of typical risk-based target levels. These summary statistics may help interpret data collected during a vapor intrusion investigation and communicate the findings of indoor air quality studies to building occupants and other stakeholders. Similar studies have been published in the past, but there has been a gradual change in indoor air quality over time and a large amount of new data has been collected, so this paper provides more relevant information for current use than previous compilations. 相似文献
This paper describes the use of three geophysical techniques to detect potential seepage that could jeopardise the integrity of reservoir embankments, could induce partial or total collapse and pose a risk to the population nearby. A fast-scanning geophysical technique using two dipole electromagnetic (EM) profile apparatus GEM2 provided the first step to detect the weakest points on the selected dams in order to proceed to a more detailed analysis and visualisation of the soil erosion (fissuring or piping) using electrical resistivity tomography (ERT). Finally, self-potential surveys were carried out to relate to the EM and ERT anomalies that could be pathways for seepage and changes of the water displacement inside the embankment. The three geophysical techniques used were evaluated in one case study of reservoir in a location relevant to flooding issues in Czech Republic. A risk approach based on the geophysical results was undertaken for the reservoir embankment. The three techniques together were compared for the same problematic section and confirmed seepage by showing similar results. Conclusions were also drawn on the efficiency of using these three techniques as a package to give a comprehensive non-invasive assessment to be used as common practice by local authorities and environment agencies whereby remedial action could be recommended to protect assets and civilians. 相似文献
Fist-sized fragments of Porites cylindrica, Porites rus and Pavona frondifera were deployed in single-species (P. cylindrica) and mixed-species (all three) plots in a shallow reef area in the northwestern Philippines. After 6 months, the corals in half of the plots were broken into smaller pieces to simulate an episodic physical disturbance. The survival of all corals was monitored from March 2000 to July 2001 during which the corals experienced 2 typhoons and episodes of algal overgrowth. For both intact and broken treatments, there was significantly higher survival in the mixed-species plots than in the single-species treatments. Fragment mortality varied between disturbances of varying frequencies and magnitudes, namely: one-time fragmentation stress, seasonal overgrowth by cyanobacteria and macroalgae, short-term (1 day) and long-term (more than 1 week) burial. The mixed-species assemblages had higher fragment survivorship than the monospecific assemblages during small-scale perturbations (e.g., algal overgrowth), but not in the face of subsequent, larger scale disturbances. This study emphasizes that coral responses to disturbance are both species- and context-specific. 相似文献
This paper evaluates convective boundary layer (CBL) budget methods as a tool for estimating regionally averaged sensible and latent heat fluxes for the study region used in OASIS (Observations at Several Interacting Scales). This is an agricultural region of mixed cropping and grazing extending about 100 km west of the town of Wagga Wagga, NSW, Australia.The analysis proceeds in three stages: first, a simpleone-dimensional model of the well-mixed layer (the CBL slab model), forced with measurements of the surface heat and evaporation fluxes, is evaluated by comparing measured and modelled CBL temperature, humidity and depths. A comparison of several entrainment schemes shows that a simple model, where the entrainment kinetic energy is parameterised as a fraction (3) of the surface sensible heat flux, works well if is set to 0.5. Second, the slab model is coupled to a Penman–Monteith model of surface evaporation to predict regional scale evaporation and thence heat fluxes. Finally, the integral CBL budget approach, which is an inverse method using theone-dimensional slab model, is used to infer regional heat and evaporation fluxes from measured time series of CBL temperature and humidity.We find that the simple CBL slab model works reasonably well for predicting CBL depth and very well for CBL temperature, especially if approximate estimates of subsidence velocity and warming due to advection are included. Regional sensible heat fluxes estimated from the integral CBL method match those measured, although the method is very sensitive to measurement errors. Measurement-model differences were larger for short integration times, because the well-mixed assumptions are violated at particular times of the day. The corollary is that `whole-day' (0530–1530 h) estimates are in reasonable agreement with measured values. Integral methods could not be used to infer the regional evaporation flux directly because CBL humidity profiles were complex and often not well mixed until mid-afternoon. We recommend that regional evaporation fluxes be predicted either from a coupled Penman–Monteith – CBL slab model, or inferred as a residual term from estimates of the regionally averaged available energy and sensible heat flux. Furthermore, we show that inferring fluxes via integral methods will always be difficult when the scalar concentrations have either a large surface source and free atmosphere sink (in the case of water vapour and methane), or a large surface sink and upper level source (in the case of CO2). 相似文献
Many actions to reduce GHG emissions have wider impacts on health, the economy, and the environment, beyond their role in mitigating climate change. These ancillary impacts can be positive (co-benefits) or negative (conflicts). This article presents the first quantitative review of the wider impacts on health and the environment likely to arise from action to meet the UK's legally-binding carbon budgets. Impacts were assessed for climate measures directed at power generation, energy use in buildings, and industry, transport, and agriculture. The study considered a wide range of health and environmental impacts including air pollution, noise, the upstream impacts of fuel extraction, and the lifestyle benefits of active travel. It was not possible to quantify all impacts, but for those that were monetized the co-benefits of climate action (i.e. excluding climate benefits) significantly outweigh the negative impacts, with a net present value of more than £85 billion from 2008 to 2030. Substantial benefits arise from reduced congestion, pollution, noise, and road accidents as a result of avoided journeys. There is also a large health benefit as a result of increased exercise from walking and cycling instead of driving. Awareness of these benefits could strengthen the case for more ambitious climate mitigation action.
Policy relevance
This article demonstrates that actions to mitigate GHG emissions have significant wider benefits for health and the environment. Including these impacts in cost–benefit analysis would strengthen the case for the UK (and similar countries) to set ambitious emissions reduction targets. Understanding co-benefits and trade-offs will also improve coordination across policy areas and cut costs. In addition, co-benefits such as air quality improvements are often immediate and local, whereas climate benefits may occur on a longer timescale and mainly in a distant region, as well as being harder to demonstrate. Dissemination of the benefits, along with better anticipation of trade-offs, could therefore boost public support for climate action. 相似文献
It has recently been suggested that the structure and strength of the meridional overturning circulation in the global ocean is governed by the input of mechanical energy to the system by winds and tides. However, it is not clear how this suggestion relates to the existence of multiple equilibria of the meridional overturning circulation, which depends on thermohaline feedbacks and is more consistent with a buoyancy-driven view of the circulation. Both theories have been illustrated by box models in the past (Stommel in Tellus 13:224–230, 1961; Gnanadesikan in Science 283:2077–2079, 1999). Here we incorporate these two theories into a single box model in an attempt to reconcile the roles of mechanical and buoyancy forcing in driving the meridional overturning circulation. The box model has two equilibrium solutions, one with sinking at high northern latitudes as in the present-day Atlantic, and one without. The circulation is mechanically driven, but the northern sinking can be thought of as a release valve which acts as a sink of potential energy when the surface water at high northern latitudes is dense enough to convect. While the source of energy comes from mechanical forcing, the presence or otherwise of multiple equilibria is therefore determined by thermohaline feedbacks. In some areas of parameter space an oscillation between the model’s two circulation regimes occurs, reminiscent of a bipolar seesaw. 相似文献
Canadian contributions to International Polar Year (IPY) 2007?C2008 were designed to improve the understanding of climate change impacts and adaptation and to gain insight into issues surrounding community health and well-being in Canada??s arctic. Fifty-two research projects, involving scientists, northern partners and communities, focused on the arctic atmosphere and climate, cryosphere, oceans, sea ice, marine ecosystems, terrestrial ecosystems, wildlife as well as human health and community well-being. Key research findings on these topics are presented in this special issue of Climatic Change. This introductory paper presents an overview of the international and Canadian IPY programs and a summary of Canadian IPY results, including progress made in data management and capacity building. The legacy of IPY in Canada includes expanded international scientific cooperation, meaningful partnerships with northern communities, and more northern residents with research training. 相似文献
Version management is a prerequisite for digital information flow between phases in the planning and building processes. Information evolves over time and many parties retrieve information from the various phases. The aim of this article is to evaluate versioning methods, focusing on geodata buildings in the 3D cadastre process. The main attention in the evaluation is on the comprehensive ISO standard Product Lifecycle Support (PLCS). PLCS is evaluated against two simpler versioning methods, the versioning in CityGML 3.0 and a modified Git versioning method implemented in CityJSON. CityGML 3.0 fulfils all but one requirement and PLCS meets all. The methods vary in complexity; the Git proposal is a simple solution, easy to implement and maintain, while PLCS includes all functionalities and is complex to implement. There is a trade‐off between number of functionalities and complexity, it is therefore important that the intended purpose determines the choice of versioning method. 相似文献