Relationship between eddy viscosity of seawater and eddy diffusivity of suspended particles

A method is described to calculate the relationship (β) between the eddy diffusivity of suspended particles and the eddy viscosity of the fluid. The data were obtained while making suspended sediment concentration measurements near the seabed on the British continental shelf. β was calculated for 0.50 size fractions and varies inversely with the suspended sediment concentration. The values were used successfully to calculate suspended sediment transport rates for separate sand fractions through a spring tidal cycle. Finally, specific values of β are suggested for varying concentrations of sand at a reference height of 100 cm above the seabed.     

Possible influence of salinity and temperature on modern shelf carbonate sedimentation

In modern, marine, carbonate sands from shelf areas between the equator and latitudes 60°S and 60°N several major grain associations can be distinguished.On open shelves (< 100 m water depth) there are two skeletal grain associations. One (chlorozoan) is virtually restricted to warm, tropical waters; the other (foramol) characterizes temperate waters but also extends into the tropics. The distribution of these two associations cannot be explained in terms of water temperature alone: salinity is suspected as being a further controlling factor. Indeed, a third skeletal association (chloralgal) appears to be characteristic of areas where salinity is higher than on open shelves.Non-skeletal grains, where present, can be grouped into two associations. In one, pellets are the only non-skeletal grains represented; in the other, ooliths and/or aggregate grains are also present. These non-skeletal associations are restricted to relatively warm waters, but temperature does not determine which one of the associations develops. Again, salinity seems important.As both salinity and temperature apparently influence the grain associations, an attempt is made to present the relationships diagrammatically. By using graph pairs of “maximum temperature/minimum salinity” and “minimum temperature/maximum salinity” (named S.T.A.R. diagrams after Salinity Temperature Annual Ranges), the various grain associations can be classed into separate salinity/temperature fields.Salinity and temperature often seem to have a mutual “compensating” effect. For example, even at high temperatures the chlorozoan association does not develop if the salinity falls below a certain value, but it develops at relatively low temperatures when salinity is sufficiently high.This “compensation” effect also appears on the S.T.A.R. diagram for non-skeletal associations. More striking here, however, is a relationship suggesting that development of the oolith/aggregate association is strongly dependent on salinity.Carbonate muds are not shown on the S.T.A.R. diagrams, but an attempt is made to assimilate them into the model.The S.T.A.R. diagrams have a predictive value. In principle, given salinity and temperature values for an area, the grain associations can be predicted. In fact, the prediction is one of “potential”, i.e. that which is to be expected provided any other necessary environmental conditions are satisfied. Predictions are presented for the shelves of an ideal ocean and of present-day oceans and seas. The S.T.A.R. diagrams thus provide the basis for a tentative global model of present-day shelf carbonate sedimentation.The special problems of land-locked seas are discussed with reference to the Mediterranean Sea and the Persian Gulf. Predictions are presented.To illustrate the possibilities of the S.T.A.R. diagram technique, an attempt at detailed prediction is given for an area — the Gulf of Batabano, Cuba — where the sediments are known and predictions can be checked.In conclusion, the problems inherent in applying the model to ancient sedimentary systems are briefly discussed.     

A controlling factor approach to estuary classification

A new approach to the classification of estuaries is described. The estuary environment classification (EEC) is based on a hierarchical view of the abiotic components that comprise the environments of estuaries. The EEC postulates that climate, oceanic, riverine and catchment factors ‘control’ a hierarchy of processes and broadly determine the physical and biological characteristics of estuaries. The classification differentiates estuaries at four levels of detail. Level 1 differentiates global scale variation based on differences in climatic and oceanic processes, which are discriminated by the factors: latitude, oceanic basins and large landmasses. Level 2 differentiates variation in estuary hydrodynamic processes, which are discriminated by estuary basin morphometry, river and oceanic forcing. Level 3 differentiates variation among estuaries that are due to catchment processes, which are discriminated by catchment geology and catchment land cover. The approach has been applied to all the estuaries in New Zealand using existing data sources. Estuaries were assigned class membership at each level of the classification by applying criteria in the form of decision rules to the database of assignment characteristics. GIS was then used to map the estuaries with classes being defined by colour at any level of the classification. The resulting map provides a multi-scale spatial framework that is suitable for many environmental or conservation management applications.     

Methods to identify and reduce potential surface stream water losses into abandoned underground mines

Methods to identify and subsequently seal surface water loss zones in stream channels were tested by the United States Bureau of Mines at Staub Run, a first-order stream near Frostburg, Maryland, that partially overlies abandoned coal mine workings. Conventional stream gauging was conducted to establish discharge patterns before and after stream sealing. Electromagnetic terrain conductivity surveys were performed within the stream channel to identify zones of increased relative water saturation to depths less than 15 m. Zones of increased conductivity were generally found to be associated with areas exhibiting statistically significant (P 0.05) gauged flow losses. Conversely, zones that exhibited declining conductivity delineated areas where between-station flows were not significantly different. Using this information on potential loss zones, an experimental grouting procedure was applied by injecting an expandable polyurethane grout to a depth less than one meter into the alluvial streambed over a 180-m section of the stream channel. Before grouting, the study section exhibited a 24 I/sec flow loss; first-phase grouting reduced this to a 14 I/sec flow loss; with a second-phase grouting the losses were only 3 I/sec.     

Assessment of annual high‐water events for the Mackenzie River basin,Canada

River ice break‐up is known to have important morphological, ecological and socio‐economic effects on cold‐regions river environments. One of the most persistent effects of the spring break‐up period is the occurrence of high‐water events. A return‐period assessment of maximum annual nominal water depths occurring during the spring break‐up and open‐water season at 28 Water Survey of Canada hydrometric sites over the 1913–2002 time period in the Mackenzie River basin is presented. For the return periods assessed, 13 (14) stations are dominated by peak events occurring during the spring break‐up (open‐water) season. One location is determined to have a mixed signal. A regime classification is proposed to separate ice‐ and open‐water dominated systems. As part of the regime classification procedure, specific characteristics of return‐period patterns including alignment, and difference between the 2 and 10‐year events are used to identify regime types. A dimensionless stage‐discharge plot allows for a contrast of the relative magnitudes of flows required to generate maximum nominal water‐depth events in the different regimes. At sites where discharge during the spring break‐up is approximately one‐quarter or greater than the magnitude of the peak annual discharge, nominal water depths can be expected to exceed those occurring during the peak annual discharge event. Several physical factors (location, basin area, stream order, gradient, river orientation, and climate) are considered to explain the differing regimes and discussed relative to the major sub‐regions of the MRB. Copyright © 2008 John Wiley & Sons, Ltd and Her Majesty the Queen in right of Canada.     

Three-dimensional simulations and wind-tunnel experiments on airflow over isolated forest stands

Prediction of windthrow risk to individual or groups of retained trees in harvested stands requires an improved understanding of canopy airflow dynamics. Large-eddy simulations were used to simulate wind-tunnel experiments in two and three dimensions to compare with observations for model validation and to address parameter space considerations for the design of subsequent retention pattern experiments. The three-dimensional simulations were similar to the observed wind-tunnel data for the statistical profiles for but there were greater differences in skewness and kurtosis. These results were obtained using a common leaf-area drag formulation without either skin friction or speed dependent drag that enables scaling with U ₀ (ambient wind speed) and h (height of the canopy). This scaling results in a single non-dimensional parameter h/h _c where h _c (x, y, z) is the momentum range resulting from the canopy drag. The validity of the model scaling was tested using two-dimensional simulations. The irrotational component of the flow (potential flow) was found to be important when defining vertical domain limitations and has significant implications for time dependent flow (i.e. turbulent conditions) when considering retention pattern design. The sudden onset of drag associated with the isolated stand presents some unexpected challenges. The horizontal scales of the shearing instabilities were simulated in two dimensions and found to range between 2h for early times to 7h for later times. The early-time horizontal scales are in the range of logical retention pattern scales and as such need to be taken into account as part of the parameter space, i.e. a range of retention pattern lengths need consideration.     

Monument-antenna effects on GPS coordinate time series with application to vertical rates in Antarctica

We examine the electromagnetic coupling of a GPS antenna–monument pair in terms of its simulated affect on long GPS coordinate time series. We focus on the Earth and Polar Observing System (POLENET) monument design widely deployed in Antarctica and Greenland in projects interested particularly in vertical velocities. We base our tests on an absolute robot calibration that included the top ~0.15 m of the monument and use simulations to assess its effect on site coordinate time series at eight representative POLENET sites in Antarctica over the period 2000.0–2011.0. We show that the neglect of this calibration would introduce mean coordinate bias, and most importantly for velocity estimation, coordinate noise which is highly sensitive to observation geometry and hence site location and observation period. Considering only sub-periods longer than 2.5 years, we show vertical site velocities may be biased by up to ±0.4 mm/year, and biases up to 0.2 mm/year may persist for observation spans of 8 years. Changing between uniform and elevation-dependent observation weighting alters the time series but does not remove the velocity biases, nor does ambiguity fixing. The effect on the horizontal coordinates is negligible. The ambiguities fixed series spectra show noise between flicker and random walk with near-white noise at the highest frequencies, with mean spectral indices (frequencies <20 cycles per year) of approximately −1.3 (uniform weighting) and −1.4 (elevation-dependent weighting). While the results are likely highly monument specific, they highlight the importance of accounting for monument effects when analysing vertical coordinate time series and velocities for the highest precision and accuracy geophysical studies.     

The economics of avoiding dangerous climate change. An editorial essay on The Stern Review

The problem of avoiding dangerous climate change requires analysis from many disciplines. Mainstream economic thinking about the problem has shifted with the Stern Review from a single-discipline focus on cost-benefit analysis to a new inter-disciplinary and multi-disciplinary risk analysis, already evident in the IPCC Third Assessment Report. This shift is more evidence of the failure of the traditional, equilibrium approach in general to provide an adequate understanding of observed behaviour, either at the micro or macro scale. The economics of the Stern Review has been accepted by governments and the public as mainstream economic thinking on climate change, when in some critical respects it represents a radical departure from the traditional treatment. The conclusions regarding economic policy for climate change have shifted from “do little, later” to “take strong action urgently, before it is too late”. This editorial sets out four issues of critical importance to the new conclusions about avoiding dangerous climate change, each of which have been either ignored by the traditional literature or treated in a misleading way that discounts the insights from other disciplines: the complexity of the global energy-economy system (including the poverty and sustainability aspects of development), the ethics of intergenerational equity, the understanding from engineering and history about path dependence and induced technological change, and finally the politics of climate policy.     

A review of global stratospheric aerosol: Measurements, importance, life cycle, and local stratospheric aerosol

Stratospheric aerosol, noted after large volcanic eruptions since at least the late 1800s, were first measured in the late 1950s, with the modern continuous record beginning in the 1970s. Stratospheric aerosol, both volcanic and non-volcanic are sulfuric acid droplets with radii (concentrations) on the order of 0.1–0.5 µm (0.5–0.005 cm^− 3), increasing by factors of 2–4 (10–10³) after large volcanic eruptions. The source of the sulfur for the aerosol is either through direct injection from sulfur-rich volcanic eruptions, or from tropical injection of tropospheric air containing OCS, SO₂, and sulfate particles. The life cycle of non-volcanic stratospheric aerosol, consisting of photo-dissociation and oxidation of sulfur source gases, nucleation/condensation in the tropics, transport pole-ward and downward in the global planetary wave driven tropical pump, leads to a quasi steady state relative maximum in particle number concentration at around 20 km in the mid latitudes. Stratospheric aerosol have significant impacts on the Earth's radiation balance for several years following volcanic eruptions. Away from large eruptions, the direct radiation impact is small and well characterized; however, these particles also may play a role in the nucleation of near tropopause cirrus, and thus indirectly affect radiation. Stratospheric aerosol play a larger role in the chemical, particularly ozone, balance of the stratosphere. In the mid latitudes they interact with both nitrous oxides and chlorine reservoirs, thus indirectly affecting ozone. In the polar regions they provide condensation sites for polar stratospheric clouds which then provide the surfaces necessary to convert inactive to active chlorine leading to polar ozone loss. Until the mid 1990s the modern record has been dominated by three large sulfur-rich eruptions: Fuego (1974), El Chichón (1982) and Pinatubo (1991), thus definitive conclusions concerning the trend of non-volcanic stratospheric aerosol could only recently be made. Although anthropogenic emissions of SO₂ have changed somewhat over the past 30 years, the measurements during volcanically quiescent periods indicate no long term trend in non-volcanic stratospheric aerosol.