Turbulent heat fluxes by profile and inertial dissipation methods: analysis of the atmospheric surface layer from shipboard measurements during the SOFIA/ASTEX and SEMAPHORE experiments     

Hélène Dupuis  Alain Weill  Kristina Katsaros  Peter K. Taylor 《Annales Geophysicae》1995,13(10):1065-1074

Heat flux estimates obtained using the inertial dissipation method, and the profile method applied to radiosonde soundings, are assessed with emphasis on the parameterization of the roughness lengths for temperature and specific humidity. Results from the inertial dissipation method show a decrease of the temperature and humidity roughness lengths for increasing neutral wind speed, in agreement with previous studies. The sensible heat flux estimates were obtained using the temperature estimated from the speed of sound determined by a sonic anemometer. This method seems very attractive for estimating heat fluxes over the ocean. However allowance must be made in the inertial dissipation method for non-neutral stratification. The SOFIA/ASTEX and SEMAPHORE results show that, in unstable stratification, a term due to the transport terms in the turbulent kinetic energy budget, has to be included in order to determine the friction velocity with better accuracy. Using the profile method with radiosonde data, the roughness length values showed large scatter. A reliable estimate of the temperature roughness length could not be obtained. The humidity roughness length values were compatible with those found using the inertial dissipation method.  相似文献   

The study of molybdenites through the¹⁸⁷Re-¹⁸⁷Os chronometer     

Jean Marc Luck  Claude J. Allègre 《Earth and Planetary Science Letters》1982,61(2):291-296

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The isotopic composition of zirconium in terrestrial and extraterrestrial samples: implications for extinct ⁹²Nb     

J.-F Minster  C.J Allègre 《Geochimica et cosmochimica acta》1982,46(4):565-573

Since Nb and Zr are only little fractionated during magmatic processes, the ⁹²Nb-⁹²Zr relative chronometer has the potential of dating the formation of the planetary bodies through their differentiation. Thus, we have analyzed the isotopic composition of zirconium in lunar, meteoritic and old and recent terrestrial samples.No isotopic variation has been found. However, the ${}^{92}\text{Zr}{}^{90}\text{Zr}$ ratio of 3.8 Ga. old zircons from the Isua acid conglomerate is on the lower limit of the range of the standard measurements. If considered an anomaly, it would correspond to a +1.5 × 10^?492Zr relative deficiency or to a 3.0 × 10^?494Zr relative excess.Our data constrain the ${}^{92}\text{Nb}{}^{93}\text{Nb}$ isotopic ratio at the time of formation of the solar system to be less than 0.007, so that the maximum sensitivity of the ⁹²Nb-⁹²Zr relative chronometer for the formation of planetary bodies is around 10⁷ a. A discussion of some possible nuclear reactions indicates that zirconium isotopic variations in zircons are not easily produced, and that the ⁹²Nb and ⁹⁴Nb natural activities (Apt et al., 1974) cannot be explained by any single one of the processes proposed so far.  相似文献   

Chemical structure and evolution of the mantle and continents determined by inversion of Nd and Sr isotopic data,I. Theoretical methods     

C.J. Allègre  S.R. Hart  J.-F. Minster 《Earth and Planetary Science Letters》1983

While the chemical structure of the earth's mantle is probably rather complex, multi-box models have been used as a first approximation to evaluate this structure. Most commonly, a three-box model is used, involving the continental crust, the upper mantle and the lower mantle. The depleted upper mantle and the continental crust are assumed to represe1nt complementary reservoirs, related by crust formation processes occurring during geologic history.Here we investigate the Rb/Sr and Sm/Nd isotopic systematics of several three-box models, using mass balance equations and the definition of the mean age of the reservoirs. The geochemical uniqueness of the models, chosen from a large family of possible models, is evaluated from elementary graph theory, and these models are then solved using a total inversion approach. This paper (Part I) describes the methodology of the procedure; the companion paper (Part II) discusses the application of this approach to multi-box mantle models.  相似文献   

Velocity constraints for the inner core inferred from long-period PKP amplitudes     

Heinz Häge 《Physics of the Earth and Planetary Interiors》1983,31(2):171-185

Long-period PKP amplitudes from 16 earthquakes in the distance range 110– 170° are compared with theoretical amplitudes which are derived from synthetic seismograms calculated for 56 systematic modifications of Earth model 1066B in the inner core. A suitable normalization procedure allows for the common representation of all observed amplitudes as a function of epicentral distance. Using the theoretical amplitude distributions it can be shown that the parameters of a regression line through the logarithmic and normalized amplitudes between 110 and 134° are related to the velocity and density jump at the inner-core boundary (ICB). The analysis shows that the dominant influence on the PKP amplitudes is the P-velocity jump which can be restricted to 0.64 ± 0.05 km s^?1. There exists a trade-off between the S-velocity jump and the density jump. Restricting the latter to the reasonable range 0–1.2 g cm^?3 the S-velocity jump at the ICB can be inferred to be 2.5–3.0 km s^?1. A rather strong S-velocity gradient below the ICB follows from the condition that the S-wave travel-time through the inner core agrees with that implied by free oscillation observations. This leads to central S-velocities between 3.81 and 4.15 km s^?1, assuming a parabolic velocity law.  相似文献   

Response of littoral chironomid communities and organic matter to late glacial lake—level,vegetation and climate changes at Lago dell’Accesa (Tuscany,Italy)     

Laurent Millet  Boris Vannière  Valérie Verneaux  Michel Magny  Jean Robert Disnar  Fatima Laggoun-Défarge  Anne Véronique Walter-Simonnet  Gilles Bossuet  Elena Ortu  Jacques-Louis de Beaulieu 《Journal of Paleolimnology》2007,38(4):525-539

This study focuses on the response of lacustrine littoral chironomid communities to late glacial changes in limnological, environmental and climate conditions in the Mediterranean context. Late glacial chironomid (Diptera: Chironomidae) assemblages, organic petrography and geochemistry were analysed in a sediment core from the littoral zone of Lago dell’Accesa (Tuscany, Italy), where the lake-level fluctuations and the vegetation history have been previously reconstructed. Comparison of the chironomid stratigraphy to other proxies (pollen assemblages, organic petrography and geochemistry, lake-level) and regional climate reconstruction suggested the predominant influence of lake-level changes on the littoral chironomid fauna. The main lowering events that occurred during the Oldest and the Younger Dryas were followed by higher proportions of taxa typical of littoral habitats. A complementary study of organic matter suggested the indirect impact of lake-level on the chironomids through changes in humic status and habitat characteristics, such as the type of substrate and aquatic macrophyte development. Several chironomid taxa, such as Glyptotendipes, Microtendipes and Cricotopus type patens, were identified as possible indicators of low lake-level in the late glacial records. Nevertheless, this study suggested that parallel analyses of organic matter and chironomid assemblages may be needed to circumvent misinterpretation of littoral chironomid assemblage stratigraphy. There was a weak response of the chironomid assemblages to small lake-level lowerings that corresponded to the Older Dryas and Preboreal oscillations. A higher level of determination, e.g. to the species group level, may be necessary to increase the sensibility of the indicators to lake-level changes.  相似文献   

Distribution of demersal fish in the south-western Barents Sea     

Ingvar Byrkjedal  & Åge Høines 《Polar research》2007,26(2):135-151

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热水沉积岩及矿物岩石标志   总被引：32，自引：2，他引：32  

肖荣阁  张汉城  陈卉泉  张宗恒 《地学前缘》2001,8(4):379-385

热水沉积物不同于普通沉积物 ,主要与热水流体类型有关。文中把热水流体划分为中高温热水流体与中低温热水流体。中高温热水沉积岩包括钾长石岩、硅质岩、电气石岩、钠长石岩、萤石岩 ;中低温热水沉积岩包括碳酸盐、硫酸盐等岩石。钾长石岩是文中确定的一种标准高温热水沉积岩 ,热水沉积钾长石以冰长石和钡长石为主 ;热水沉积碳酸盐矿物一般为铁、镁、锰、钙碳酸盐 ,碳酸盐的形成与CO2 和H2 O的不混溶温度有关 ,一般在不混溶温度 ,即 2 66℃以下生成 ,或在海水补偿线以上形成。热水沉积岩中有热水交代蚀变岩夹层 ,尤其是在高温热水活动区 ,可以交代泥质、钙泥质沉积物形成热水交代沉积岩 ,包括方柱石黑云母岩、透辉石透闪石岩、夕卡岩、绿泥石岩等。根据对霍各乞铜多金属矿床的研究 ,热水交代透辉石透闪石岩的稀土总量较低 ,表现为轻稀土富集 ,重稀土亏损 ,稀土配分模式表现为正Eu异常  相似文献   

Stochastic delineation of wellhead protection area in fractured aquifers and parametric sensitivity study   总被引：1，自引：0，他引：1  

S. Chevalier  M. A. Buès  J. Tournebize  O. Banton 《Stochastic Environmental Research and Risk Assessment (SERRA)》2001,15(3):205-227

 In many countries, the setup of protection areas around every drinking water well was instituted at a national level in order to preserve the quality of water as well as the perennially of the resource. Wellhead protection surfaces have been defined using capture zones showing the area influenced by a well within a certain time. A stochastic method is developed for delineating time-related capture zones in fractured aquifers characterised by a low porosity and a high degree of fracturing. The flow velocity within the fractures is determined statistically depending on the distribution of the fracture features and the mass transfer solution is obtained through a particle tracking algorithm. Probabilistic capture zone curves are obtained as a function of the travel time of particles to the well and the percentage of particles apt to be extracted up to this time. A sensitivity study of fracture network parameters leads to the conclusion that orientations and aperture distribution of the fracture sets are of primary importance to the wellhead protection delineation.  相似文献   

Petrogenesis of the amphibole-rich veins from the Lherz orogenic lherzolite massif (Eastern Pyrenees, France): a case study for the origin of orthopyroxene-bearing amphibole pyroxenites in the lithospheric mantle     

J. Fabriès  J.-P. Lorand  M. Guiraud 《Contributions to Mineralogy and Petrology》2001,140(4):383-403

The Lherz orogenic lherzolite massif (Eastern French Pyrenees) displays one of the best exposures of subcontinental lithospheric mantle containing veins of amphibole pyroxenites and hornblendites. A reappraisal of the petrogenesis of these rocks has been attempted from a comprehensive study of their mutual structural relationships, their petrography and their mineral compositions. Amphibole pyroxenites comprise clinopyroxene, orthopyroxene and spinel as early cumulus phases, with garnet and late-magmatic K₂O-poor pargasite replacing clinopyroxene, and subsolidus exsolution products (olivine, spinel II, garnet II, plagioclase). The original magmatic mineralogy and rock compositions were partly obscured by late-intrusive hornblendites and over a few centimetres by vein–wallrock exchange reactions which continued down to subsolidus temperatures for Mg–Fe. Thermobarometric data and liquidus parageneses indicate that amphibole pyroxenites started to crystallize at P ≥ 13 kbar and recrystallized at P < 12 kbar. The high Al^VI/Al^IV ratio (>1) of clinopyroxenes, the early precipitation of orthopyroxene and the late-magmatic amphibole are arguments for parental melts richer in silica but poorer in water than alkali basalts. Their modelled major element compositions are similar to transitional alkali basalt with about 1–3 wt% H₂O. In contrast to amphibole pyroxenites, hornblendites only show kaersutite as liquidus phase, and phlogopite as intercumulus phase. They are interpreted as crystalline segregates from primary basanitic magmas (mg=0.6; 4–6 wt% H₂O). These latter cannot be related to the parental liquids of amphibole pyroxenites by a fractional crystallization process. Rather, basanitic liquids mostly reused pre-existing pyroxenite vein conduits at a higher structural level (P ≤ 10 kbar). A continuous process of redox melting and/or alkali melt/peridotite interaction in a veined lithospheric mantle is proposed to account for the origin of the Lherz hydrous veins. The transitional basalt composition is interpreted in terms of extensive dissolution of olivine and orthopyroxene from wallrock peridotite by alkaline melts produced at the mechanical boundary layer/thermal boundary layer transition (about 45–50 km deep). Continuous fluid ingress allowed remelting of the deeper veined mantle to produce the basanitic, strongly volatiles enriched, melts that precipitated hornblendites. A similar model could be valid for the few orthopyroxene-rich hydrous pyroxenites described in basalt-hosted mantle xenoliths. Received: 15 September 1999 / Accepted: 31 January 2000  相似文献