This paper briefly presents the West African Monsoon (WAM) Modeling and Evaluation Project (WAMME) and evaluates WAMME general circulation models’ (GCM) performances in simulating variability of WAM precipitation, surface temperature, and major circulation features at seasonal and intraseasonal scales in the first WAMME experiment. The analyses indicate that models with specified sea surface temperature generally have reasonable simulations of the pattern of spatial distribution of WAM seasonal mean precipitation and surface temperature as well as the averaged zonal wind in latitude-height cross-section and low level circulation. But there are large differences among models in simulating spatial correlation, intensity, and variance of precipitation compared with observations. Furthermore, the majority of models fail to produce proper intensities of the African Easterly Jet (AEJ) and the tropical easterly jet. AMMA Land Surface Model Intercomparison Project (ALMIP) data are used to analyze the association between simulated surface processes and the WAM and to investigate the WAM mechanism. It has been identified that the spatial distributions of surface sensible heat flux, surface temperature, and moisture convergence are closely associated with the simulated spatial distribution of precipitation; while surface latent heat flux is closely associated with the AEJ and contributes to divergence in AEJ simulation. Common empirical orthogonal functions (CEOF) analysis is applied to characterize the WAM precipitation evolution and has identified a major WAM precipitation mode and two temperature modes (Sahara mode and Sahel mode). Results indicate that the WAMME models produce reasonable temporal evolutions of major CEOF modes but have deficiencies/uncertainties in producing variances explained by major modes. Furthermore, the CEOF analysis shows that WAM precipitation evolution is closely related to the enhanced Sahara mode and the weakened Sahel mode, supporting the evidence revealed in the analysis using ALMIP data. An analysis of variability of CEOF modes suggests that the Sahara mode leads the WAM evolution, and divergence in simulating this mode contributes to discrepancies in the precipitation simulation. 相似文献
This study investigated the seasonal changes in carbon (C) and nitrogen (N) stable isotope values of several typical food sources of Apostichopus japonicus in a farm pond, including particulate organic matter (POM), macroalgae, benthic microalgae and animals such as nematode and copepod. The stable isotope technique was used to quantify relative contributions of various sources to the food uptake by A. japonicus. The results showed that significant changes occurred in the C and N stable isotope values of sea cucumber food sources due to the seasonality of micro-or macroalgae prosperity and the fluctuation of environmental conditions. The sea cucumber A. japonicus exhibited corresponding alterations in feeding strategy in response to the changes in food conditions. Calculation with a stable isotope mixing model showed that macroalgae was the principal food source for A. japonicus throughout the 1-yr investigation, with the relative contribution averaging 28.1% - 63.2%. The relative contributions of other food sources such as copepod and nematode, POM, benthic microalgae to the total food uptake by sea cucumber averaged 22.6% - 39.1%, 6.3% - 22.2%, 2.8% - 6.5%, and 2.8% - 4.2%, respectively. Together these results indicated that the seasonal changes in food sources led to the obvious temporal differences in the relative contribution of various food sources utilized by A. japonicus. Such findings provide the basic scientific information for improving the aquaculture techniques of A. japonicus, particularly for optimizing the food environment of A. japonicus culture in farm ponds. 相似文献
The 1981–82 Solar Mesosphere Explorer (SME) mission is described. The SME experiment will provide a comprehensive study of mesospheric ozone and the processes which form and destroy it. Five instruments will be carried on the spinning spacecraft to measure the ozone density and its altitude distribution from 30 to 80 km, monitor the incoming solar ultraviolet radiation, and measure other atmospheric constituent which affect ozone. The polar-orbiting spacecraft will be placed into a 3pm-3 am Sun-synchronous orbit. The atmospheric measurements will scan the Earth's limb and measure: (1) the mesospheric and stratospheric ozone density distribution by inversion of Rayleigh-scattered ultraviolet limb radiance, and the thermal emission from ozone at 9.6 m; (2) the water vapor density distribution by inversion of thermal emission at 6.3 m; (3) the ozone photolysis rate by inversion of the O2(1g) 1.27 m limb radiance; (4) the temperature profile by a combination of narrow-band and wide-band measurements of the 15 m thermal emission by CO2; and, (5) theNO2 density distribution by inversion of Rayleighscattered limb radiance at 0.439 m. The solar ultraviolet monitor will measure both the 0.2–0.31 m spectral region and the Lyman-alpha (0.1216 m) contribution to the solar irradiance. This combination of measurements will provide a rigorous test of the photochemical equilibrium theory of the mesospheric oxygen-hydrogen system, will determine what changes occur in the ozone distribution as a result of changes in the incoming solar radiation, and will detect changes that may occur as a result of meteorological disturbances. 相似文献
Uranium mineralization in Madyalabodu area, Cuddapah district, Andhra Pradesh, is spatially related to chloritized and brecciated quartzite of the Gulcheru Formation in the immediate vicinity of E-W to ESE-WNW trending basic dyke. Chloritization transgresses the lithological boundaries. Whole-rock geochemical data indicate enrichment of MgO and Al2O3 coupled with depletion of SiO2, Na2O, K2O, CaO and TiO2 in the chlorite-rich zone. Fe2O3 and FeO do not vary significantly in the altered and the unaltered zones. Electron Probe Microanalysis (EPMA) data reveal that the chlorites in contact with uranium minerals are enriched in MgO and depleted in FeO than in the others. Considering the petrological evidence, geochemical signature and structural constraints, it appears that chlorite acted more as an adsorbent rather than as a reductant in facilitating uranium mineralization. Uraninite crystallized later from the uranium originally adsorbed on chlorites. Chloritization might also have facilitated mineralization through the generation of nascent hydrogen, H2S and lowering pH of uranium-bearing solution. 相似文献
The effects of Cd on the adsorption of an aquatic fulvic acid (FA) to the surface of Bacillus subtilis were investigated from pH 2.5 to 7.0, at fixed ionic strength (0.1 M NaClO4) and at ambient temperature (22 °C). Cd (14 mg/l) had no effect on FA adsorption at pH<5 but increased FA adsorption at pH>6. The effects of Cd (0, 14 mg/l) on FA adsorption to B. subtilis were further examined as a function of initial FA concentration (0–45 mg C/l) at pH 6.5. FA adsorption isotherms also were measured at pH 6.5 as a function of dissolved Cd concentration (0–14 mg/l) at three initial FA concentrations (4, 8, 22 mg C/l). At all FA concentrations studied at pH 6.5, FA adsorption increased with increasing initial total Cd concentration.
Under all studied conditions, preferential adsorption of high- to intermediate-molecular-weight FA components to B. subtilis resulted in a fractionation of the FA pool, with lower-molecular-weight components remaining in solution. At pH>6, Cd further enhanced the adsorption of high- to intermediate-molecular-weight FA components but did not significantly enhance the adsorption of lower-molecular-weight components. Hence, the overall process of adsorptive fractionation was not altered significantly by the presence of Cd.
Overall, the results of this study (1) demonstrate that FA adsorption to bacterial surfaces can be altered by the presence of a metal cation, and (2) provide further evidence that microbe–metal–ligand interactions may significantly affect the mobility and fate of natural organic matter in the subsurface. 相似文献
A devastating landslide on 18 August 1998 near Malpa Village in Kali Valley of Higher Kumaun Himalaya killed 221 persons. The landslide was a complex rock fall–debris flow. The mass movement generated around one million cubic metres of debris and partially blocked the Kali River, Malpa Gad (a tributary of Kali) being blocked completely. The rock mass failed primarily due to the near vertical slopes hanging over the valley along joints, the formation of structural wedges along the free face, the sheared rock mass due to the close proximity of major tectonic planes, and the enhanced pore–water pressure due to prolonged heavy precipitation in the preceding days. The mesoscopic shear zone, exhibiting ramp and flat structure in quartzites, shows a southward thrust movement that might have generated shear stress in the rocks. The slide clearly demonstrates the distressed state of the rock mass in the Himalayan region due to the ongoing northward drift of the Indian plate. 相似文献
Laboratory experiments and numerical simulations in homogeneous porous media were used to investigate the influence of porous medium wettability on the formation and growth of preferential dissolution pathways, dissolution fingers, during nonaqueous phase liquid (NAPL) dissolution. As the porous medium became increasingly NAPL-wet, dissolution fingers grew wider and slower. This result was observed in physical experiments with 0% and 100% NAPL-wet conditions and confirmed with numerical simulations at these and intermediate wettabilities. A previously derived expression for an upscaled mass transfer rate coefficient that accounts for the growth of dissolution fingers was used to quantify the effect of fingering on overall NAPL removal rates. For the test cases evaluated, NAPL dissolution fingering controlled the overall rate of NAPL dissolution after the dissolution front moved 4 cm in 0% NAPL-wet conditions and 18 cm in 100% NAPL-wet conditions. Thus, even in completely NAPL-wet media dissolution fingering may control the overall rate of NAPL dissolution after relatively short travel distances. The importance of NAPL dissolution fingering in heterogeneous systems with spatially varying NAPL saturations, though, remains an important question for future work. 相似文献