Influence of bottom topography roughness on the jet and inertial recirculation of a mid-latitude gyre     

Bernard Barnier  Christian Le Provost 《Dynamics of Atmospheres and Oceans》1993,18(1-2)

Several numerical experiments are conducted to examine the influence of mesoscale, bottom topography roughness on the inertial circulation of a wind-driven, mid-latitude ocean gyre. The ocean model is based on the quasi-geostrophic formulation, and is eddy-resolving as it features high vertical and horizontal resolutions (six layers and a 10 km grid). An antisymmetrical double-gyre wind stress curl forces the baroclinic modes and generates a strong surface jet. In the case of a flat bottom, inertia and inverse energy cascade force the barotropic mode, and the resulting circulation features strong, barotropic, inertial gyres. The sea-floor roughness inhibits the inertial circulation in the deep layers; the barotropic component of the flow is then forced by eddy-topography interactions, and its energy concentrates at the scales of the topography. As a result, the baroclinicity of the flow is intesified: the barotropic mode is reduced with regard to the baroclinic modes, and the bottom flow (constrained by the mesoscale sea-floor roughness) is decoupled from the surface flow (forced by the gyre-scale wind). Rectified, mesoscale bottom circulation induces an interfacial form stress at the thermocline, which enhances horizontal shear instability and opposes the eastward penetration of the jet. The mean jet is consequently shortened, but the instantaneous jet remains very turbulent, with meanders of large meridional extent. The sea-floor roughness modifies the energy pathways, and the eddies have an even more important role in the establishment of the mean circulation: below the thermocline, rectification processes are dominant, and eddies transfer energy toward permanent mesoscale circulations strongly correlated with topography, whereas above the thermocline mean flow and eddy generation are influenced by the mean bottom circulation through interfacial stress. The topography modifies the vorticity of the barotropic and highest baroclinic modes. Vorticity accumulates at the small topographic scales, and the vorticity content of the highest modes, which is very weak in the flat-bottom case, increases significantly. Few changes occur in surface-intensified modes. In the deep layers of the model, the inverse correlation between relative vorticity and topography at small scales ensures the homogenization of the potential vorticity, which mainly retains the largest scales of the bottom flow and the scale of β.  相似文献   

Development of a High Magnification Enlarger     

R P Dubey  N D Christian  K D Mallick 《Journal of the Indian Society of Remote Sensing》1991,19(4):277-286

Visual interpretation forms the basis for many operational applications of remote sensing. Suitable enlargement of remotely sensed data by optical projection is a basic requirement for visual interpretation. High Magnification Enlarger (HME) is a versatile interpretation aid developed for achieving wide-ranging scale transfer and variable-magnification display from a standard 24 cm format transparency. It operates on the principle of optical projection and is configured as a vertical column mounted unit. Low-distortion, high-quality enlarging lenses coupled with accuracy of alignment ensure accurate reproduction of the scale and the finer details from the input image transparency. Maximum user convenience is achieved by motorization of various controls.  相似文献   

Heavy metal pollution in the Arcachon Basin (France) : Bonding states     

Christian Carruesco  Yvon Lapaquellerie 《Marine pollution bulletin》1985,16(12):493-497

Information available (since 1977) from a great many recent surveys on the Arcachon Basin has enabled us to determine three characteristic environments and study the behaviour of heavy metals (Ni, Cu, Zn, Pb, Cd, Hg). The relationship between heavy metals and grain-size fractions has been determined after having specified whether metals were preferentially organically or inorganically bound. This study has allowed us to establish the origin (natural or anthropogenic) of metallic enrichment and assess the extent of pollution.  相似文献   

Coesite and pure pyrope in high-grade blueschists of the Western Alps: a first record and some consequences   总被引：55，自引：0，他引：55  

Christian Chopin 《Contributions to Mineralogy and Petrology》1984,86(2):107-118

A pyrope-quartzite originally described by Vialon (1966) from the Dora Maira massif was resampled and reinvestigated. Garnet (up to 25 cm in size), phengite, kyanite, talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz. The garnet is a pyrope-almandine solid solution with 90 to 98 mol % Mg end-member. It contains inclusions of coesite which has partially inverted to quartz, resulting in a typical radial cracking of the host garnet around the inclusions. Several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite. The formidable pressures of formation implied (≧28 kbar) are independently indicated by i) the coexistence of nearly pure pyrope with free silica and talc, ii) the coexistence of jadeite with kyanite, iii) the high Si content of phengite. Water activity must have been low. The stability of talc-phengite and the presence of rare glaucophane inclusions in pyrope point to low formation temperatures (about 700 °C) and to a probable Alpine age for the assemblage. This is evidence that low temperature gradients, how essentially transient they are, may nevertheless persist to considerable depths. Moreover, the upper crustal (evaporite-related?) origin of the quartzite and its interbedding within a continental unit implies that continental crust may also be subducted to depths of 90 km or more. The return back to the surface is problematic; the retrograde assemblages observed show that it must be tectonic. If the rocks remain at depth, new perspectives open for the genesis of intermediate to acidic magmas. Eventually, the role of continental crust in geodynamics may have to be reconsidered.  相似文献   

Reply to ‘comments and further analysis on effective roughness lengths for use in numerical three-dimensional models’, by P. Taylor     

Jean-Claude André  Christian Blondin 《Boundary-Layer Meteorology》1987,39(4):419-419

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Sulfide and platinum mineralization in the Merensky Reef: evidence from hydrous silicates and fluid inclusions   总被引：5，自引：1，他引：5  

Christian G. Ballhaus  Eugen F. Stumpfl 《Contributions to Mineralogy and Petrology》1986,94(2):193-204

The base metal sulfides of the Merensky Reef are associated with hydrous silicates and intense deuteric hydrous alteration of cumulus and postcumulus silicates. Biotite and phlogopite crystallized in the vicinity of sulfides from a volatile-enriched highly fractionated intercumulus melt. Amphibole, chlorite, and talc are later alteration phases of cumulus pyroxene and intercumulus plagioclase. Biotite is often accompanied by zircon, rutile, and quartz. Accessory quartz hosts a complex suite of H₂O-NaCl-(CaCl₂)-CO₂-CH₄ fluid inclusions which have thus far not been described from the Merensky Reef. The earliest fluid inclusion compositions are NaCl-(H₂O) with less than 10 vol.% water; CO₂ coexisting with a halite daughter crystal and brine; and polyphase inclusions with up to six daughter and accidental phases and high contents of divalent cations. The maximum trapping temperature is around 730° C at 4 to 5 kb pressure. Later inclusion generations are H₂O-NaCl, CO₂-H₂O, and pure CO₂ and CH₄. The presence of Cl-rich fluids during the intercumulus stage of the crystallizing Merensky Reef is directly related to the mode of sulfide precipitation. Prior to sulfide unmixing in a hydrous magma sulfur is likely to be present as H₂S. Sulfur saturation causes reaction of H₂S with oxides of the silicate melt to form a sulfide melt plus water. During reaction the magma is enriched in water until a separate fluid unmixes. It carries all compounds with high fluid/melt partition coefficients, as well as metals capable of forming OH- and Cl-complexes. Precious metals are assumed to have fractionated into the Cl-rich fluid as Cl-complexes rather than being dissolved in the sulfide melt. During the cooling evolution of the fluid the precious elements precipitate around the periphery of sulfide melt droplets. The model proposed explains the distribution pattern of platinum-group minerals in the Merensky Reef better than any orthomagmatic mineralization concept offered so far.  相似文献   

Impact glasses from Zhamanshin crater (U.S.S.R.): chemical composition and discussion of origin     

Christian Koeber  Kurt Fredriksson 《Earth and Planetary Science Letters》1986,78(1)

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A comparison of two avalanche-models with exemplary avalanches of Tyrol and Switzerland and the effects to hazard zoning     

Christian Weiler 《Surveys in Geophysics》1995,16(5-6):671-679

For the purposes of a thesis at the Institute of avalanche and torrent control at the university of agriculture in Vienna a comparison of two avalanche-models, a hydraulic one from Voellmy/Salm/Gubler and a statistical one from Laatsch/Zenke/Dankerl with exemplary exactly known avalanches of Tyrol and Switzerland was started in 1993. The result of this work was that both models failed by the calculation of avalanches with high recurrence intervals (over 300 years). For the calculation of avalanches with recurrence intervals under 300 years the results of both models are regular. The conclusion is that a combination of two models i.e. a hydraulic one improved by statistical calculations will be the best.  相似文献   

Unconvincing evidence against the blocking temperature concept?     

Christian Chopin  Henri Maluski 《Contributions to Mineralogy and Petrology》1982,80(4):386-390

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Mössbauer studies of synthetic and natural micas on the polylithionite-siderophyllite join: reply     

Christian Levillain  Pierre Maurel  Francis Menil 《Physics and Chemistry of Minerals》1982,8(2):99-100

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