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331.
Abstract A model with two active layers, a mixed layer and a pycnocline layer, over a semipassive deep ocean is described. The model is used to simulate a climatological seasonal cycle in the upper North Pacific. The formulation is similar to that in Cherniawsky et al. (1990). The model resolution is 1° latitude by 1.5° longitude, extending from 62°N to the equator. It is driven with monthly wind stress (Hellerman and Rosenstein, 1983) and with Newtonian heat and freshwater fluxes, which were inferred from climatological (Levitus, 1982) sea‐surface monthly temperatures and annual mean salinities. The monthly temperature anomalies (without the annual mean) are multiplied by a prescribed gain factor and advanced in time, compensating for time delay in the response of the mixed layer. No‐slip and no‐flux constraints are applied on north, east, west and land boundaries, while the following open boundary conditions are used at the equator: (a) free‐slip on zonal velocities in the two layers; (b) a prescribed meridional transport, due to local curl of the wind stress, in the mixed layer; (c) an antisymmetric meridional velocity plus a small flux‐balancing term in the second layer; and (d) across‐equator symmetry for layer depths, temperatures and salinities. Sensitivity to two aspects of parametrization is investigated: (1) the change to horizontal diffusion/viscosity coefficients that depend on the velocity deformation field (as in Smagorinsky, 1963), and (2) the use of idealized piecewise‐linear profiles for second‐layer temperatures and salinities for calculating mixed layer entrainment fluxes. 相似文献
332.
The use of rural areas by the urban population is an important organizing principle in the study of the rural hinterland of urban centers. One of the important land uses identified within the urban field is recreation. This paper focuses on cottage property ownership in one part of the urban field, the rural-recreational countryside. Using three case studies from Canada, it was found that cottage properties account for a large proportion of local residential property. Although most cottage properties are owned by urban residents, up to one-quarter are owned by local residents. Using a questionnaire survey, it was also found that cottage owners are more likely to be older, better educated, and have higher incomes than rural residents. 相似文献
333.
Greg Van den Bleeken Othmar Müntener Peter Ulmer 《Contributions to Mineralogy and Petrology》2011,161(6):921-945
Melt-rock reaction in the upper mantle is recorded in a variety of ultramafic rocks and is an important process in modifying
melt composition on its way from the source region towards the surface. This experimental study evaluates the compositional
variability of tholeiitic basalts upon reaction with depleted peridotite at uppermost-mantle conditions. Infiltration-reaction
processes are simulated by employing a three-layered set-up: primitive basaltic powder (‘melt layer’) is overlain by a ‘peridotite
layer’ and a layer of vitreous carbon spheres (‘melt trap’). Melt from the melt layer is forced to move through the peridotite
layer into the melt trap. Experiments were conducted at 0.65 and 0.8 GPa in the temperature range 1,170–1,290°C. In this P-T
range, representing conditions encountered in the transition zone (thermal boundary layer) between the asthenosphere and the
lithosphere underneath oceanic spreading centres, the melt is subjected to fractionation, and the peridotite is partially
melting (T
s ~ 1,260°C). The effect of reaction between melt and peridotite on the melt composition was investigated across each experimental
charge. Quenched melts in the peridotite layers display larger compositional variations than melt layer glasses. A difference
between glasses in the melt and peridotite layer becomes more important at decreasing temperature through a combination of
enrichment in incompatible elements in the melt layer and less efficient diffusive equilibration in the melt phase. At 1,290°C,
preferential dissolution of pyroxenes enriches the melt in silica and dilutes it in incompatible elements. Moreover, liquids
become increasingly enriched in Cr2O3 at higher temperatures due to the dissolution of spinel. Silica contents of liquids decrease at 1,260°C, whereas incompatible
elements start to concentrate in the melt due to increasing levels of crystallization. At the lowest temperatures investigated,
increasing alkali contents cause silica to increase as a consequence of reactive fractionation. Pervasive percolation of tholeiitic
basalt through an upper-mantle thermal boundary layer can thus impose a high-Si ‘low-pressure’ signature on MORB. This could
explain opx + plag enrichment in shallow plagioclase peridotites and prolonged formation of olivine gabbros. 相似文献