Impact of southeast Indian Ocean sea surface temperature anomalies on monsoon-ENSO-dipole variability in a coupled ocean–atmosphere model     

Pascal Terray  Fabrice Chauvin  Hervé Douville 《Climate Dynamics》2007,28(6):553-580

Recent studies show that SouthEast Indian Ocean (SEIO) SSTs are a highly significant precursor of transitions of the whole monsoon-El Niño-Southern Oscillation (ENSO) system during recent decades. However, the reasons for this specific interannual variability have not yet been identified unequivocally from the observations. Among these, the possibility of SEIO SST-driven variability in the monsoon-ENSO system is investigated here by inserting positive/negative SEIO temperature anomalies in the February’s restart files of a state-of-the-art coupled General Circulation Model (GCM) for 49 years of a control simulation. For each year of the control simulation, the model was then integrated for a 1-year period in fully coupled mode. These experiments show that Indian Summer Monsoon (ISM) and tropical Indian Ocean Dipole Mode (IODM) events are significantly influenced by the SEIO temperature perturbations inserted in the mixed layer of the coupled GCM several months before. A warm SEIO perturbation, inserted in late boreal winter, slowly propagates northward during the following seasons, implies enhanced ISM rainfall and finally triggers a negative IODM pattern during boreal fall in agreement with observations. A reversed evolution is simulated for a cold SEIO perturbation. It is shown that the life cycle of the simulated SEIO signal is driven by the positive wind-evaporation-SST, coastal upwelling and wind-thermocline-SST feedbacks. Further diagnosis of the sensitivity experiments suggests that stronger ISM and IODM variabilities are generated by excluding the El Niño years of the control simulation or when the initial background state in the SEIO is warmer. This finding confirms that IODM events may be triggered by multiple factors, other than ENSO, including subtropical SEIO SST anomalies. However, the ENSO mode does not react significantly to the SEIO temperature perturbation in the perturbed runs even though the simulated Pacific pattern agrees with the observations during boreal fall. These discrepancies with the observations may be linked to model biases in the Pacific and to the too strong ENSO simulated by this coupled GCM. These modeling evidences confirm that subtropical Indian Ocean SST anomalies generated by Mascarene high pulses during austral summer are a significant precursor of both ISM and IODM events occuring several months later.  相似文献   

Comparison of wind and wave measurements and models in the Western Mediterranean Sea   总被引：2，自引：0，他引：2  

Fabrice Ardhuin  Luciana Bertotti  Jean-Raymond Bidlot  Luigi Cavaleri  Valentina Filipetto  Jean-Michel Lefevre  Paul Wittmann 《Ocean Engineering》2007,34(3-4):526-541

We have hindcast the wind and wave conditions in the Mediterranean Sea for two one month periods. Four different meteorological models and three different wave models have been used. The results have been compared with satellite and buoy wind and wave observations.Several conclusions concerning both the instruments and the models have been derived. The quality of both wind and wave results has been assessed. Close to the coasts high resolution, nested wave models are required for sufficient reliability.A wave threshold analysis suggests a sufficient reliability only off the coast, with a substantial decrease for low wave heights.  相似文献   

Numerical analysis of canister movements in an engineered barrier system     

Fabrice Dupray  Lyesse Laloui 《Acta Geotechnica》2016,11(1):145-159

The mid-term safety of deep geological nuclear waste repositories is based in part on the presence of a buffer, the main role of which is to isolate the environment from radionuclides. A design evaluation of such a repository is necessary to assess the potential vertical canister movement inside the drift that could reduce the buffer efficiency. A thermo-hydro-mechanical (THM) simulation is performed in a vertical cross-section of the drift. The THM couplings are described, and their influences on the mid-term (300 years) response of the engineered barrier system (EBS) are revealed. This study uses an advanced constitutive model to simulate the THM processes that occur in a specific EBS design case. The near-field simulations of the nuclear waste canister are performed in a two-dimensional finite element configuration that considers the effect of gravity. The focus of this study is on the mechanical behaviour of the buffer, which consists of two different forms of bentonite. Such an approach allows realistic consideration of the effect of the wetting and drying of the buffer material in non-isothermal conditions. Due to a specific design that includes bentonite blocks and pellets, the canister is observed to heave slightly during the re-saturation period, which extends up to 100 years.  相似文献   

Understanding single-station ground motion variability and uncertainty (sigma): lessons learnt from EUROSEISTEST     

Olga-Joan Ktenidou  Zafeiria Roumelioti  Norman Abrahamson  Fabrice Cotton  Kyriazis Pitilakis  Fabrice Hollender 《Bulletin of Earthquake Engineering》2018,16(6):2311-2336

Accelerometric data from the well-studied valley EUROSEISTEST are used to investigate ground motion uncertainty and variability. We define a simple local ground motion prediction equation (GMPE) and investigate changes in standard deviation (σ) and its components, the between-event variability (τ) and within-event variability (φ). Improving seismological metadata significantly reduces τ (30–50%), which in turn reduces the total σ. Improving site information reduces the systematic site-to-site variability, φ _S2S (20–30%), in turn reducing φ, and ultimately, σ. Our values of standard deviations are lower than global values from literature, and closer to path-specific than site-specific values. However, our data have insufficient azimuthal coverage for single-path analysis. Certain stations have higher ground-motion variability, possibly due to topography, basin edge or downgoing wave effects. Sensitivity checks show that 3 recordings per event is a sufficient data selection criterion, however, one of the dataset’s advantages is the large number of recordings per station (9–90) that yields good site term estimates. We examine uncertainty components binning our data with magnitude from 0.01 to 2 s; at smaller magnitudes, τ decreases and φ _SS increases, possibly due to κ and source-site trade-offs Finally, we investigate the alternative approach of computing φ _SS using existing GMPEs instead of creating an ad hoc local GMPE. This is important where data are insufficient to create one, or when site-specific PSHA is performed. We show that global GMPEs may still capture φ _SS , provided that: (1) the magnitude scaling errors are accommodated by the event terms; (2) there are no distance scaling errors (use of a regionally applicable model). Site terms (φ _S2S ) computed by different global GMPEs (using different site-proxies) vary significantly, especially for hard-rock sites. This indicates that GMPEs may be poorly constrained where they are sometimes most needed, i.e., for hard rock.  相似文献   

Influence of the microstructural properties of biocemented sand on its mechanical behavior     

Abdelali Dadda  Christian Geindreau  Fabrice Emeriault  Annette Esnault Filet  Aurélie Garandet 《国际地质力学数值与分析法杂志》2019,43(2):568-577

The mechanical efficiency of the biocementation process is directly related to the microstructural properties of the biocemented sand, such as the volume fraction of calcite, its distribution within the pore space, coordination number, contact surface area, and types of contact. In the present work, some of these microscopic properties are computed, from 3D images obtained by X-ray tomography of biocemented sand. These properties are then used as an input in current analytical models to estimate the elastic properties (Young and shear moduli) and the strength properties (Coulomb cohesion). For the elastic properties, the analytical estimates (contact cement theory model) are compared with classical bounds, self-consistent estimate and numerical results obtained by direct computation (FEM computation) on the same 3D images. Concerning the cohesion, an analytical model initially developed to estimate the cohesion due to suction in unsaturated soils is modified to evaluate the macroscopic cohesion of biocemented sands. Such analytical model is calibrated on experimental data obtained from triaxial tests performed on the same biocemented sand. In overall, the presented results point out the important role of some microstructural parameters, notably those related to the contact, on such effective parameters.  相似文献   

Apparent discrepancy in contamination history of a sub-tropical estuary evaluated through 210Pb profile and chronostratigraphical markers     

Marques AN  Monna F  da Silva Filho EV  Fernex FE  Fernando Lamego Simões Filho F 《Marine pollution bulletin》2006,52(5):532-539

Zn and Cd concentrations, stable lead isotopes and ²¹⁰Pb-derived chronology were determined in a sediment core sampled at Sepetiba Bay (South-eastern Brazil). During the last decades, the bay’s watershed has been modified by the increase of industrial activities and human interventions. In particular, Zn and Cd ore treatment plants were built near the coast in 1960 and 1970, respectively, and water has been diverted from the adjacent Paraíba do Sul River watershed since 1950. The core collected at shallow depth near the industrial area exhibits four successive events: (i) at 50 cm depth, a change in the ²⁰⁶Pb/²⁰⁷Pb ratio from about 1.162 to more than 1.18 might be the result of the São Francisco Channel opening and water diversion from Paraíba do Sul river; (ii) at 40 cm depth, Zn concentration starts to increase (up to 0.8 mg g⁻¹) (iii) above 30 cm depth, relatively high Cd concentrations (up to 1.6 μg g⁻¹) are observed and (iv) at 16 cm depth, change in unsupported ²¹⁰Pb slope is probably related to a waste dam built to prevent strong metal contamination in the bay. Sediment accumulation rates evaluated by Zn and Cd profiles used as time-markers are higher than those calculated from ²¹⁰Pb-based chronology models. Using the constant initial concentration (CIC) model both events are supposed to date back to about 1884 and 1902, respectively, while using the constant rate of supply (CRS) model it shifts to about 1925 and 1935. Such discrepancies are probably assigned to the fact that these models do not take into account site-specific local sedimentation dynamics. In the study area, particles deposition seems to be controlled by enrichment with unsupported ²¹⁰Pb transported by runoff from a mangrove flat bank. Chronology derived from a model that assumes an exponential increase of the initial ²¹⁰Pb activity fits well with the estimated rates obtained from historical events.  相似文献   

Surface properties, solubility and dissolution kinetics of bamboo phytoliths   总被引：4，自引：0，他引：4  

Fabrice Fraysse  Oleg S. Pokrovsky  Jacques Schott 《Geochimica et cosmochimica acta》2006,70(8):1939-1951

Although phytoliths, constituted mainly by micrometric opal, exhibit an important control on silicon cycle in superficial continental environments, their thermodynamic properties and reactivity in aqueous solution are still poorly known. In this work, we determined the solubility and dissolution rates of bamboo phytoliths collected in the Réunion Island and characterized their surface properties via electrophoretic measurements and potentiometric titrations in a wide range of pH. The solubility product of “soil” phytoliths ( at 25 °C) is equal to that of vitreous silica and is 17 times higher than that of quartz. Similarly, the enthalpy of phytoliths dissolution reaction is close to that of amorphous silica but is significantly lower than the enthalpy of quartz dissolution. Electrophoretic measurements yield isoelectric point pH_IEP = 1.2 ± 0.1 and 2.5 ± 0.2 for “soil” (native) and “heated” (450 °C heating to remove organic matter) phytoliths, respectively. Surface acid-base titrations allowed generation of a 2-pK surface complexation model. Phytoliths dissolution rates, measured in mixed-flow reactors at far from equilibrium conditions at 2 ? pH ? 12, were found to be intermediate between those of quartz and vitreous silica. The dissolution rate dependence on pH was modeled within the concept of surface coordination theory using the equation: