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A two-dimensional numerical model is applied to a coastal ocean wherein alongshore elevation and density gradients, normally calculated by a three-dimensional model, are instead supplied by climatologically averaged data for the California Current System between 25 and 40°N. Surface wind stress is also obtained from climatological data. Both surface and bottom boundary layers are resolved in the model calculations; a second moment turbulence closure submodel supplies vertical diffusivities. Near steady state solutions are possible when surface buoyancy flux is imposed at the surface.Model results are as follows: Southward wind stress produces a broad equatorward current with an embedded coastal jet in accordance with previous studies. Positive wind stress curl reduces the jet current and produces a poleward undercurrent which then surfaces as the curl is increased. The jet currents are reduced and poleward flow increases as bottom steepness increases; to a lesser extent, inclusion of the beta effect has a similar effect. The existence of near bottom, poleward or equatorward flow is explained rather simply in terms of the bottom stress resulting from the alongshore balance of surface wind stress and vertically integrated pressure gradient, the latter involving the alongshore surface elevation and density gradient. A further finding is that the upwelling circulation associated with wind stress is confined to the top 200 to 300 m of the ocean along the California coast. 相似文献
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This paper extends the evidence that volcanic rocks may contain initial argon, and investigates some of the implications of the results.The incorporation of initial argon with a composition different to that of air at the time of crystallisation may be an important cause of scatter of K-Ar dates in areas such as the British Tertiary igneous province, but in favourable circumstances the correct age may be recovered.An age of about 60 Ma is indicated for the lavas of Northern Ireland. 相似文献
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Christopher J. Mellor Stephen J. Dugdale Grace Garner Alexander M. Milner 《水文科学杂志》2017,62(4):499-514
The impact of climate change on Arctic rivers is expected to be severe. There is therefore a need for greater understanding of Arctic river temperature processes. This study quantifies the spatio-temporal variability of water temperatures in the Kårsa River, Sweden. Water temperature was monitored over two summers within the main proglacial channel and within braids fed by different sources. Longitudinal and lateral temperature patterns were assessed in relation to prevailing hydro-meteorology. Temperature metrics in the main channel increased with distance downstream but were moderated by a large lake, while temperatures in the braids were dependent upon channel source. The high temperature standard deviation and inter-site differences within the braids highlight the importance of braided channels for creating thermal habitat heterogeneity. Temperatures were dependent on hydro-meteorological conditions, with sensitivity to air temperature maximized during cooler, rainy conditions. These results shed new light on Arctic river temperature patterns and their controlling processes. 相似文献
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Concentrations of polycyclic aromatic hydrocarbons were determined in species of commercial fish and lobsters following an oil-spill just off the protected Madagascan coastline. Samples were collected along the coastline within and outside the affected area. Summed PAH concentrations ranged from 1.9 μg kg−1 to 63 μg kg−1 wet weight, but with no higher molecular weight PAHs (>202 Da) being detected. All concentrations of benzo[a]pyrene, benz[a]anthracene and dibenz[a,h]anthracene were <0.1 μg kg−1 wet weight, well within the EU and UK set limits for the protection of human health. Additionally, samples were calculated as the benzo[a]pyrene toxic equivalency quotient (TEQ) and found to be well below the level of concern in relation to health of human consumers. Evaluation of the biota PAH data indicated the origin of PAH was predominantly petrogenic with >80% arising from oil sources. Profile studies indicate a low-level multisource petrogenic contamination probably representing a pre-spill background for the area. 相似文献
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Sensitivity studies with a new generalized coordinate ocean model are performed in order to compare the behavior of bottom boundary layers (BBLs) when terrain-following (sigma or combined sigma and z-level) or z-level vertical grids are used, but most other numerical aspects remain unchanged. The model uses a second-order turbulence closure scheme that provides surface and BBL mixing and results in a quite realistic climatology and deep water masses after 100 year simulations with a coarse resolution (1° × 1°) basin-scale terrain-following grid. However, with the same turbulence scheme but using a z-level grid, the model was unable to produce dense water masses in the deep ocean. The latter is a known problem for coarse resolution z-level models, unless they include highly empirical BBL schemes.A set of dense water overflow experiments with high-resolution grids (10 and 2.5 km) are used to investigate the influence of model parameters such as horizontal diffusivity, vertical mixing, horizontal resolution, and vertical resolution on the simulation of bottom layers for the different coordinate systems. Increasing horizontal diffusivity causes a thinner BBL and a bottom plume that extends further downslope in a sigma grid, but causes a thicker BBL and limited downslope plume extension in a z-level grid. A major difference in the behavior of the BBL in the two grids is due to the larger vertical mixing generated by the turbulence scheme over the step-like topography in the z-level grid, compared to a smaller vertical mixing and a more stably stratified BBL in the sigma grid. Therefore, the dense plume is able to maintain its water mass better and penetrates farther downslope in the sigma grid than in the z-level grid. Increasing horizontal and vertical resolution in the z-level grid converges the results toward those obtained by a much coarser resolution sigma coordinate grid, but some differences remain due to the basic differences in the mixing process in the BBL. 相似文献
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The Gulf Stream system has been numerically simulated with relatively high resolution and realistic forcing. The surface fluxes
of the simulation were obtained from archives of calculations from the Eta-29 km model which is an National Center for Environment
Prediction (NCEP) operational atmospheric prediction model; synoptic fields are available every 3 hour. A comparison between
experiments with and without surface fluxes shows that the effect of the surface wind stress and heat fluxes on the Gulf Stream
path and separation is closely related to the intensification of deep circulations in the northern region. Additionally, the
separation of the Gulf Stream and the downslope movement of the Deep Western Boundary Current (DWBC) are reproduced in the
model results. The model DWBC crosses under the Gulf Stream southeast of Cape Hatteras and then feeds the deep cyclonic recirculation
east of the Bahamas. The model successfully reproduces the cross-sectional vertical structures of the Gulf Stream, such as
the asymmetry of the velocity profile, and this structure is sustained along the downstream axis. The distribution of Root
Mean Square (RMS) elevation anomaly of the model shows that the eddy activity of the Gulf Stream is realistically reproduced
by the model physics. The entrainment of the upper layer slope current into the Gulf Stream occurs near cross-over; the converging
cross-stream flow is nearly barotropic.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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The isotopic composition and concentration of Pb was measured in suspended particulate matter of the Irish Sea. Aerosol, surficial and pre-industrial sediment was also analysed to provide information on sources terms. Concentrations of Pb in suspended sediments were lower than previously reported which presumably reflects the international effort to reduce Pb inputs to the environment. Lead concentrations were highest in Liverpool Bay and lowest in the western Irish Sea. A significant negative relationship between Pb and salinity suggests that present inputs and the resuspension of relict lead associated with particles in areas significantly affected by freshwater discharges are the predominant sources of Pb to the Irish Sea. The isotopic composition of Pb in the stratified region of the western Irish Sea demonstrates that atmospheric sources are also significant to this region, which is consistent with current knowledge on the hydrography. Pb isotopic ratios show that water entering the Irish Sea through St George's Channel is significantly influenced by anthropogenic inputs prior to additional contamination by direct inputs to the Irish Sea. 相似文献
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Tidal flow characteristics in the Hudson-Raritan Estuary are studied with a two-dimensional, depth-averaged finite difference model. Rivers are modeled as one-dimensional channels with variable width and depth and are calculated as part of the two-dimensional calculations at no extra computational cost. An extensive comparison of numerical, tidal calculations with observational data than has previously appeared in the literature is presented. Computed velocity and tidal elevation fields compare well with observations. Comparison with observations at the Sandy Hook-Rockaway Point transect indicates that the barotropic tidal residual current contributes significantly to the overall steady circulation in the harbor. The residual current is mainly induced by the coastal geometry and bottom topography through the nonlinear inertia effects. 相似文献