Inconsistencies between cpx-grt geothermometry and field observations: example of the peraluminous eclogites from Beni Bousera (North Morocco)     

Hassan Chrifi Alaoui  Jacques Kornprobst  Didier Laporte 《地学学报》1997,9(2):83-86

Large variations in clinopyroxene-garnet (cpx-grt) temperatures are recorded in thin peraluminous eclogite layers from Beni Bousera ultramafic massif (Morocco): cpx-grt temperatures in the core of layers < 20 cm thick are higher by up to 300°C than in the margins. The cpx-grt temperatures are correlated to both Al-concentration in cpx and Ca-concentration in grt, the two latter parameters being themselves closely intercorrelated. It is demonstrated that the regular interaction parameter Δw^grt_Ca calculated from the Beni Bousera natural data is very close to Δw^grt_Ca calculated from experimental data analysis for Ca-rich garnet. It is concluded that: (i) Al-concentration in cpx has no significant effect on the distribution of Fe and Mg between cpx and grt; and (ii) cpx-grt temperature variations observed across Beni Bousera peraluminous eclogite layers do not correspond to real thermal gradients, but merely result from the inadequacy of the thermometric equations in Ca-rich systems (X^grt_Ca > 0.15).  相似文献   

Trends and climate evolution: Statistical approach for very high temperatures in France   总被引：3，自引：0，他引：3  

Sylvie Parey  Farida Malek  Carine Laurent  Didier Dacunha-Castelle 《Climatic change》2007,81(3-4):331-352

The existence of an increasing trend in average temperatures during the last 50 years is widely acknowledged. Furthermore, there is compelling evidence of the variability of extremes, and rapid strides are made in studies of these events. Indeed, by extending the results of the “extreme value theory” (EVT) to the non-stationary case, analyses can examine the presence of trends in extreme values of stochastic processes. Definition of extreme events, their statistical significance as well as their interpretations have to be handled with great care when used for environmental concerns and public safety. Thus, we will discuss the validity of the hypothesis allowing the use of mathematical theories for these problems. To answer safety requirements, respect installation norms and reduce public risk, return levels are a major operational goal, obtained with the EVT. In this paper, we give quantitative results for observations of high temperatures over the 1950–2003 period in 47 stations in France. We examined the validity of the non-stationary EVT and introduced the notion of return levels (RL) in a time-varying context. Our analysis puts particular accent on the difference between methods used to describe extremes, to perform advanced fits and tests (climatic science), and those estimating the probability of rare future events (security problems in an evolving climate). After enouncing the method used for trend identification of extremes in term of easily interpretable parameters of distribution laws, we apply the procedure to long series of temperature measurements and check the influence of data length on trend estimation. We also address the problem of choosing the part of observations allowing appropriate extrapolation. In our analysis, we determined the influence of the 2003 heat wave on trend and return-level estimation comparing it to the RL in a stationary context. The application of the procedure to 47 stations spread over France is a first step for a refined spatial analysis. Working on the behavior of distribution parameters while assessing trend identification is a primary tool in order to classify climatic change with respect to the location of the station and open a systematic work using the same methodology for other variables and multivariate studies.  相似文献   

Quantitative evaluation of soil processes using in situ-produced cosmogenic nuclides     

Erik Thorson Brown  Fabrice Colin  Didier L. Bourls 《Comptes Rendus Geoscience》2003,335(16):1161-1171

In situ-produced cosmogenic nuclides provide a means for quantitative evaluation of a wide range of weathering and sediment transport processes. Although these nuclides have received attention for their power as geochronometers of surface exposure, it may be argued that they are more broadly suited for study of surface processes. In many environments, they may be used to evaluate collapse, erosion, burial, bioturbation, and creep, as well as providing a qualitative basis for distinguishing allochthonous from autochthonous materials. In addition, these nuclides can provide quantitative information on rates of erosion on scales of landforms and drainage basins. Here, we review the systematics of cosmogenic nuclide production within the Earth's surface, and present field examples demonstrating the utilization of in situ-produced cosmogenic nuclides distributions for evaluation of a range of soil evolution processes. To cite this article: E.T. Brown et al., C. R. Geoscience 335 (2003).  相似文献   

A Graph Clustering Approach to Localization for Adaptive Covariance Tuning in Data Assimilation Based on State-Observation Mapping     

Cheng  Sibo  Argaud  Jean-Philippe  Iooss  Bertrand  Ponçot  Angélique  Lucor  Didier 《Mathematical Geosciences》2021,53(8):1751-1780

Mathematical Geosciences - An original graph clustering approach for the efficient localization of error covariances is proposed within an ensemble-variational data assimilation framework. Here,...  相似文献   

Seasonal variability of the equatorial undercurrent termination and associated salinity maximum in the Gulf of Guinea     

Nicolas Kolodziejczyk  Frédéric Marin  Bernard Bourlès  Yves Gouriou  Henrick Berger 《Climate Dynamics》2014,43(11):3025-3046

The termination of the Equatorial Undercurrent (EUC) in the eastern equatorial Atlantic during boreal summer and fall, and the fate of the associated saline water masses, are analyzed from in situ hydrological and currents data collected during 19 hydrographic cruises between 2000 and 2007, complemented by observations from Argo profiling floats and PIRATA moorings, and from a numerical simulation of the Tropical Atlantic Ocean for the period 1993–2007. An intense variability of the circulation and hydrological properties is evidenced from observations in the upper thermocline (24.5–26.2 isopycnal layer) between June and November. During early boreal summer, saline water masses are transported eastward in the upper thermocline to the African coast within the EUC, and recirculate westward on both sides of the EUC. In mid-boreal summer, the EUC weakens in the upper thermocline and the equatorial salinity maximum disappears due to intense mixing with the surface waters during the upwelling season. The extra-equatorial salinity maxima are also partially eroded during the boreal summer, with a slight poleward migration of the southern hemisphere maximum until late boreal summer. The upper EUC reappears in September, feeding again the eastern equatorial Atlantic with saline waters until boreal spring. During December–January, numerical results suggest a second seasonal weakening of the EUC in the Gulf of Guinea, with a partial erosion of the associated equatorial salinity maximum.  相似文献   

Stable isotopes (2H, 18O and 13C) in groundwaters from the northwestern portion of the Guarani Aquifer System (Brazil)     

Didier Gastmans  Hung Kiang Chang  Ian Hutcheon 《Hydrogeology Journal》2010,18(6):1497-1513

The groundwater flow pattern of the western part of the Guarani Aquifer System (GAS), Brazil, is characterized by three regional recharge areas in the north, and a potentiometric divide in the south, which trends north–south approximately. Groundwater flow is radial from these regional recharge areas toward the center of Paraná Sedimentary Basin and toward the western outcrop areas at the border of the Pantanal Matogrossense, because of the potentiometric divide. The isotopic composition of GAS groundwater leads to understanding the paleoclimatic conditions in the regional recharge areas. The δ¹⁸O and δ²H isotopic ratios of GAS groundwaters vary, respectively, from –9.1 to –4.8‰ V-SMOW and –58.4 to –21.7‰ V-SMOW. In the recharge zones, enriched δ¹⁸O values are observed, while in the confined zone lighter δ¹⁸O values are observed. These suggest that climatic conditions were 10°C cooler than the present during the recharge of these waters. The δ¹³C ratios in groundwater of GAS, in the study area, vary from –19.5 to –6.5‰ VPDB, increasing along the regional flow lines toward the confined zone. This variation is related to dissolution of carbonate cement in the sandstones.  相似文献   

History Matching Geostatistical Model Realizations Using a Geometrical Domain Based Parameterization Technique     

Didier Yu Ding  Frédéric Roggero 《Mathematical Geosciences》2010,42(4):413-432

Reservoir characterization needs the integration of various data through history matching, especially dynamic information such as production or 4D seismic data. Although reservoir heterogeneities are commonly generated using geostatistical models, random realizations cannot generally match observed dynamic data. To constrain model realizations to reproduce measured dynamic data, an optimization procedure may be applied in an attempt to minimize an objective function, which quantifies the mismatch between real and simulated data. Such assisted history matching methods require a parameterization of the geostatistical model to allow the updating of an initial model realization. However, there are only a few parameterization methods available to update geostatistical models in a way consistent with the underlying geostatistical properties. This paper presents a local domain parameterization technique that updates geostatistical realizations using assisted history matching. This technique allows us to locally change model realizations through the variation of geometrical domains whose geometry and size can be easily controlled and parameterized. This approach provides a new way to parameterize geostatistical realizations in order to improve history matching efficiency.  相似文献   

Slant Column Measurements of O3 and NO2 During the NDSC Intercomparison of Zenith-Sky UV-Visible Spectrometers in June 1996     

H. K. Roscoe  P. V. Johnston  M. Van Roozendael  A. Richter  A. Sarkissian  J. Roscoe  K. E. Preston  J-C. Lambert  C. Hermans  W. DeCuyper  S. Dzienus  T. Winterrath  J. Burrows  F. Goutail  J-P. Pommereau  E. D'Almeida  J. Hottier  C. Coureul  R. Didier  I. Pundt  L. M. Bartlett  C. T. McElroy  J. E. Kerr  A. Elokhov  G. Giovanelli  F. Ravegnani  M. Premuda  I. Kostadinov  F. Erle  T. Wagner  K. Pfeilsticker  M. Kenntner  L. C. Marquard  M. Gil  O. Puentedura  M. Yela  D. W. Arlander  B. A. Kastad Hoiskar  C. W. Tellefsen  K. Karlsen Tornkvist  B. Heese  R. L. Jones  S. R. Aliwell  R. A. Freshwater 《Journal of Atmospheric Chemistry》1999,32(2):281-314

In June 1996, 16 UV-visible sensors from 11 institutes measured spectra of the zenith sky for more than 10 days. Spectra were analysed in real-time to determine slant column amounts of O3 and NO2. Spectra of Hg lamps and lasers were measured, and the amount of NO2 in a cell was determined by each spectrometer. Some spectra were re-analysed after obvious errors were found. Slant columns were compared in two ways: by examining regression analyses against comparison instruments over the whole range of solar zenith angles; and by taking fractional differences from a comparison instrument at solar zenith angles between 85° and 91°. Regression identified which pairs of instruments were most consistent, and so which could be used as universal comparison instruments. For O3, regression slopes for the whole campaign agreed within 5% for most instruments despite the use of different cross-sections and wavelength intervals, whereas similar agreement was only achieved for NO2 when the same cross-sections and wavelength intervals were used and only one half-day's data was analysed. Mean fractional differences in NO2 from a comparison instrument fall within ±7% (1-sigma) for most instruments, with standard deviations of the mean differences averaging 4.5%. Mean differences in O3 fall within ±2.5% (1- sigma) for most instruments, with standard deviations of the mean differences averaging 2%. Measurements of NO2 in the cell had similar agreement to measurements of NO2 in the atmosphere, but for some instruments measurements with cell and atmosphere relative to a comparison instrument disagreed by more than the error bars.  相似文献   

Estimating water fluxes in the critical zone using water stable isotope approaches in the Groundnut and Ferlo basins of Senegal     

Djim M. L. Diongue  Christine Stumpp  Olivier Roupsard  Didier Orange  Frederic C. Do  Serigne Faye 《水文研究》2023,37(1):e14787

Sustainable water management in semi-arid agriculture practices requires quantitative knowledge of water fluxes within the soil-vegetation-atmosphere system. Therefore, we used stable-isotope approaches to evaluate evaporation (E_a), transpiration (T_a), and groundwater recharge (R) at sites in Senegal's Groundnut basin and Ferlo Valley pasture region during the pre-monsoon, monsoon, and post-monsoon seasons of 2021. The approaches were based upon (i) the isothermal evaporation model (for quantifying E_a); (ii) water and isotope mass balances (to partition E_a and T_a for groundnut and pasture); and (iii) the piston displacement method (for estimating R). E_a losses derived from the isothermal evaporation model corresponded primarily to Stage II evaporation, and ranged from 0.02 to 0.09 mm d⁻¹ in the Groundnut basin, versus 0.02–0.11 mm d⁻¹ in Ferlo. At the groundnut site, E_a rates ranged from 0.01 to 0.69 mm d⁻¹; T_a was in the range 0.55–2.29 mm d⁻¹; and the T_a/ET_a ratio was 74%–90%. At the pasture site, the ranges were 0.02–0.39 mm d⁻¹ for E_a; 0.9–1.69 mm d⁻¹ for T_a; and 62–90% for T_a/ET_a. The ET_a value derived for the groundnut site via the isotope approach was similar to those from eddy covariance measurements, and also to the results from the previous validated HYDRUS-1D model. However, the HYDRUS-1D model gave a lower T_a/ET_a ratio (23.2%). The computed groundwater recharge for the groundnut site amounted to less than 2% of the local annual precipitation. Recommendations are made regarding protocols for preventing changes to isotopic compositions of water in samples that are collected in remote arid regions, but must be analysed days later. The article ends with suggestions for studies to follow up on evidence that local aquifers are being recharged via preferential pathways.  相似文献