Null Variance Altitudes for the photolysis rate constants of species with barometric distribution: Illustration on Titan upper atmosphere modeling     

Zhe Peng  Fabien Cailliez  Michel Dobrijevic  Pascal Pernot 《Icarus》2012,218(2):950-955

The precision of the rates of the photolysis processes initiating the complex chemistry of Titan’s upper atmosphere conditions strongly the predictivity of photochemical models. Recent studies in sensitivity analysis of such models point out photolysis rate constants as key parameters. However, they have been treated approximately so far. We deal here directly with uncertainty in the absorption cross-sections to derive the uncertain altitude-dependent photolysis rate constants. We observe that the uncertainty on the photolysis rate constants of the major species, N₂ and CH₄, varies strongly with altitude and rather surprisingly vanishes at specific altitudes. We propose a simple model to interpret these features and we demonstrate that they are transferable to any major absorber distributed barometrically in an atmosphere.  相似文献   

The influence of paleoclimatic events on the functioning of an alpine thermal system (France): the contribution of hydrodynamic–thermal modeling     

Stéphanie Gallino  Jean-Yves Josnin  Marc Dzikowski  Fabien Cornaton  Dominique Gasquet 《Hydrogeology Journal》2009,17(8):1887-1900

Numerical models of the Aix-les-Bains thermal aquifer (France) were used to investigate the influence of Quaternary paleoclimatic events on the current thermal state of the groundwater. Initial numerical tests were successful in that present-day fluid flows (heads and flow rates) and the resulting velocities were compatible with residence time data. Water flowing through an aquifer cools the rock mass; therefore, the rate of water flow governs the outlets temperature. For the Aix-les-Bains aquifer, applying present-day flow rates to the entire history of the aquifer leads to much more substantial cooling of the rock mass than is indicated by the outlets temperature (i.e. present-day flow rates are 10 times too high). This suggests that the aquifer may have gone through alternating functioning phases, during which the rock mass cooled, and blocked phases, during which the aquifer reheated. Other results indicate that the main parameters affecting thermal behavior during a functioning phase are the total inflow volume, rather than individual inflow rates, and the initial heat field. As phenomena linked to glaciation can lead to the blocking of infiltration zones and aquifer outlets, the findings suggest that the hypothesis of intermittent aquifer functioning related to glaciations is compatible with the current thermal field.  相似文献   

The East Caledonian Current: A Case Example for the Intercomparison between AltiKa and In Situ Measurements in a Boundary Current     

Fabien Durand  Frédéric Marin  Jean-Luc Fuda  Thierry Terre 《Marine Geodesy》2017,40(1):1-22

This paper presents an assessment of SARAL/AltiKa satellite altimeter for the monitoring of a tropical western boundary current in the south-western Pacific Ocean: the East Caledonian Current. We compare surface geostrophic current estimates obtained from two versions of AltiKa along-track sea level height (AVISO 1 Hz and PEACHI 40 Hz) with two kinds of dedicated in situ datasets harvested along the satellite ground tracks: one deep-ocean current-meter mooring deployed in the core of the boundary current and five glider transects. It is concluded that the AltiKa-derived current successfully captures the velocity of the boundary current, with a standard error of 11 cm/s with respect to the in situ data. It also appears important to reference AltiKa sea level anomaly to the latest mean dynamic topography available in our area. Doing so, Ka-band altimetry provides a satisfactory representation of the western boundary current. Thereby, it usefully contributes to observing its variability in such a remote and under-observed ocean region. However, the rather long repeat period of SARAL (35 days) in comparison to the high frequency variability seen in the flow velocity of the boundary current calls for a combined use of SARAL with the other satellite altimetry missions.  相似文献   

In situ characterization of serpentinites from forearc mantle wedges: Timing of serpentinization and behavior of fluid-mobile elements in subduction zones     

Fabien Deschamps  Stéphane Guillot  Marguerite Godard  Catherine Chauvel  Muriel Andreani  Kéiko Hattori 《Chemical Geology》2010,269(3-4):262-277

The Tso Morari serpentinites in the Ladakh area, northwest Himalaya, originated from the forearc mantle overlying the northward subducting Neo-Tethys lithosphere and the margin of the Indian continent. The serpentinites are characterized by high concentration of fluid-mobile elements (FME: As, Sb, B, Li, and U) compared to ophiolitic or abyssal serpentinites. The Pb isotopic compositions of serpentinites show influence of the subducted Indian continental lithosphere. Trace element concentrations of antigorite determined in situ with Laser Ablation High Resolution Inductively Coupled Mass Spectrometer (LA-HR-ICP-MS) show high contents of FME including Pb, in contrast to the spatially associated iron oxides. Rare earth elements (REE) and compatible elements, such as Sc and Co, remained immobile during the hydration, allowing the identification of the primary minerals (olivine or orthopyroxene) from which serpentine formed. Serpentinized olivine displays higher Sb and As concentrations (up to 1000 × PM) than serpentinized orthopyroxenes that are enriched in Pb, Cs and Li (2 to up to 10 × PM).We propose that the observed FME distribution in two types of serpentine reflect the differential incorporation of FME during the downward movement of the serpentinite along the subduction plane. At temperature lower than 400 °C, at shallow depths, olivine is preferentially serpentinized and incorporates elements that are fluid soluble at low temperatures, such as Sb and As. Above 400 °C, orthopyroxene is hydrated and incorporates Pb, Cs, Li and possibly Ba. Boron and U are incorporated in both types of serpentine suggesting that they are released from slabs at temperatures around 300–400 °C. The serpentine acts as a sink for water, but also for FME and transports them to deeper and hotter levels in the mantle, down to the isotherm 600–650 °C where dehydration occurs.  相似文献   

Noble gas enrichments in porewater of estuarine sediments and their effect on the estimation of net denitrification rates     

Fabien Pitre 《Geochimica et cosmochimica acta》2010,74(2):531-4243

The concentration and the isotopic ratios of noble gases He, Ne, Ar, Kr and Xe were measured in porewater trapped in shallow sediments of the estuary of the St-Lawrence River, Québec, Canada. The gases are atmospheric in origin but most samples have gas concentrations 1.7-28 times higher than those expected in solution in water at equilibrium with the atmosphere. Elemental fractionation of heavier noble gases Kr and Xe compared to Ar strongly suggests that noble gases were adsorbed on sediments or organic matter and then desorbed into porewaters due to depressurization, as collected samples were brought to the surface. Atmospheric Ar in porewater is used as a reference to measure the N₂-fluxes at the water-sediment interface. Ignoring the Ar enrichments observed in porewater could lead to a severe underestimation of the denitrification rate in oceans and estuaries.  相似文献   

Modelling the global ocean tides: modern insights from FES2004   总被引：30，自引：2，他引：30  

Florent Lyard  Fabien Lefevre  Thierry Letellier  Olivier Francis 《Ocean Dynamics》2006,56(5-6):394-415

During the 1990s, a large number of new tidal atlases were developed, primarily to provide accurate tidal corrections for satellite altimetry applications. During this decade, the French tidal group (FTG), led by C. Le Provost, produced a series of finite element solutions (FES) tidal atlases, among which FES2004 is the latest release, computed from the tidal hydrodynamic equations and data assimilation. The aim of this paper is to review the state of the art of tidal modelling and the progress achieved during this past decade. The first sections summarise the general FTG approach to modelling the global tides. In the following sections, we introduce the FES2004 tidal atlas and validate the model against in situ and satellite data. We demonstrate the higher accuracy of the FES2004 release compared to earlier FES tidal atlases, and we recommend its use in tidal applications. The final section focuses on the new dissipation term added to the equations, which aims to account for the conversion of barotropic energy into internal tidal energy. There is a huge improvement in the hydrodynamic tidal solution and energy budget obtained when this term is taken into account.  相似文献   

Fluid-dynamics driving saline water in the North East German Basin   总被引：2，自引：0，他引：2  

Fabien Magri  Ulf Bayer  Christoph Jahnke  V. Clausnitzer  H. J. Diersch  J. Fuhrman  P. Möller  A. Pekdeger  M. Tesmer  H. J. Voigt 《International Journal of Earth Sciences》2005,94(5-6):1056-1069

In several areas of the North German Basin, saline water comes close to, or even reaches the surface. Available data from wells indicate that brine stratification is under unstable conditions in the deeper underground. In order to analyse the possible transport mechanisms, 3D thermohaline simulations have been carried out for two different scenarios. The 3D regional model (230×330 km) indicates that salty water is driven to the surface by hydrostatical forces from the surrounding highlands. In addition, a smaller scale model (10×10 km) has been constructed with a grid resolution accounting for possible convective flow. The results indicate that convective flow may play a dominant role in areas with minor topography. In summary, the complex pattern of near surface occurrences of saline water probably results from the interaction of hydrostatic and thermal forces.  相似文献   

How to anchor hotspots in a convecting mantle?     

Anne Davaille  Fabien GirardMichael Le Bars 《Earth and Planetary Science Letters》2002,203(2):621-634

Laboratory experiments were performed to study the influence of density and viscosity layering on the formation and stability of plumes. Viscosity ratios ranged from 0.1 to 6400 for buoyancy ratios between 0.3 and 20, and Rayleigh numbers between 10⁵ and 2.10⁸. The presence of a chemically stratified boundary layer generates long-lived thermochemical plumes. These plumes first develop from the interface as classical thermal boundary layer instabilities. As they rise, they entrain by viscous coupling a thin film of the other layer and locally deform the interface into cusps. The interfacial topography and the entrainment act to further anchor the plumes, which persist until the chemical stratification disappears through entrainment, even for Rayleigh numbers around 10⁸. The pattern of thermochemical plumes remains the same during an experiment, drifting only slowly through the tank. Scaled to an Earth’s mantle without plate tectonics, our results show that: (1) thermochemical plumes are expected to exist in the mantle, (2) they could easily survive hundreds of millions of years, depending on the size and magnitude of the chemical heterogeneity on which they are anchored, and (3) their drift velocity would be at most 1-2 mm/yr. They would therefore produce long-lived and relatively fixed hotspots on the lithosphere. However, the thermochemical plumes would follow any large scale motion imposed on the chemical layer. Therefore, the chemical heterogeneity acts more as a ‘floating anchor’ than as an absolute one.  相似文献   

Electrochemical properties of solids at the aqueous–solid interface and heterogeneity of surfacePropriétés électrochimiques des solides à l'interface solide–eau et hétérogénéité de surface     

Fabien Thomas  Bénédicte Prélot  Frédéric Villiéras  Jean-Maurice Cases 《Comptes Rendus Geoscience》2002,334(9):633-648

In aqueous medium, solid surfaces are in general electrically charged. The induced electrical and chemical properties govern numerous phenomena, such as colloidal stability or transport of pollutants. Numerous industrial processes make use of these properties. The understanding of the underlying mechanisms at molecular level is of high importance in order to predict and master the behaviour of dispersed matter in the environment and in industrial processes. The present paper shows the evolution of theories and experimental methods, their recent developments and applications. To cite this article: F. Thomas et al., C. R. Geoscience 334 (2002) 633–648.  相似文献   

Salinization problems in the NEGB: results from thermohaline simulations   总被引：1，自引：0，他引：1  

Fabien Magri  Ulf Bayer  Maja Tesmer  Peter Möller  Asaf Pekdeger 《International Journal of Earth Sciences》2008,97(5):1075-1085

The occurrence of salty waters close to the surface is a well-known problem in the North East German Basin. Previous numerical simulations showed that near-surface brine occurrences are due to the interaction of hydrostatic and thermally induced forces (mixed convection). The influence of hydraulic permeabilities and thermal conductivities on the observed patterns remained an open question. Based on a hydro-geochemical dataset, thermohaline simulations are carried out in order to quantify the impact of these physical parameters on brine migration. The results indicate that the salinity and temperature profiles are strongly controlled by hydraulic permeabilities and can locally be influenced by thermal conductivities.  相似文献