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231.
Bruno Franco Xavier Fettweis Michel Erpicum Samuel Nicolay 《Climate Dynamics》2011,36(9-10):1897-1918
The atmosphere?Cocean general circulation models (AOGCMs) used for the IPCC 4th Assessment Report (IPCC AR4) are evaluated for the Greenland ice sheet (GrIS) current climate modelling. The most suited AOGCMs for Greenland climate simulation are then selected on the basis of comparison between the 1970?C1999 outputs of the Climate of the twentieth Century experiment (20C3M) and reanalyses (ECMWF, NCEP/NCAR). This comparison indicates that the representation quality of surface parameters such as temperature and precipitation are highly correlated to the atmospheric circulation (500?hPa geopotential height) and its interannual variability (North Atlantic oscillation). The outputs of the three most suitable AOGCMs for present-day climate simulation are then used to assess the changes estimated by three IPCC greenhouse gas emissions scenarios (SRES) over the GrIS for the 2070?C2099 period. Future atmospheric circulation changes are projected to dampen the zonal flow, enhance the meridional fluxes and therefore provide additional heat and moisture to the GrIS, increasing temperature over the whole ice sheet and precipitation over its northeastern area. We also show that the GrIS surface mass balance anomalies from the SRES A1B scenario amount to ?300?km3/year with respect to the 1970?C1999 period, leading to a global sea-level rise of 5?cm by the end of the 21st century. This work can help to select the boundaries conditions for AOGCMs-based downscaled future projections. 相似文献
232.
Mitigating the heat stress via a derivative policy is a vital financial option for agricultural producers and other business sectors to strategically adapt to the climate change scenario. This study has provided an approach to identifying heat stress events and pricing the heat stress weather derivative due to persistent days of high surface air temperature (SAT). Cooling degree days (CDD) are used as the weather index for trade. In this study, a call-option model was used as an example for calculating the price of the index. Two heat stress indices were developed to describe the severity and physical impact of heat waves. The daily Global Historical Climatology Network (GHCN-D) SAT data from 1901 to 2007 from the southern California, USA, were used. A major California heat wave that occurred 20-25 October 1965 was studied. The derivative price was calculated based on the call-option model for both long-term station data and the interpolated grid point data at a regular 0.1 ×0.1 latitude-longitude grid. The resulting comparison indicates that (a) the interpolated data can be used as reliable proxy to price the CDD and (b) a normal distribution model cannot always be used to reliably calculate the CDD price. In conclusion, the data, models, and procedures described in this study have potential application in hedging agricultural and other risks. 相似文献
233.
234.
The removal of Mn(II) from coal mine drainage (CMD) by chemical addition/active treatment can significantly increase treatment costs. Passive treatment for Mn removal involves promotion of biological oxidative precipitation of manganese oxides (MnOx). Manganese(II) removal was studied in three passive treatment systems in western Pennsylvania that differed based on their influent Mn(II) concentrations (20–150 mg/L), system construction (±inoculation with patented Mn(II)-oxidizing bacteria), and bed materials (limestone vs. sandstone). Manganese(II) removal occurred at pH values as low as 5.0 and temperatures as low as 2 °C, but was enhanced at circumneutral pH and warmer temperatures. Trace metals such as Zn, Ni and Co were removed effectively, in most cases preferentially, into the MnOx precipitates. Based on synchrotron radiation X-ray diffraction and Mn K-edge extended X-ray absorption fine structure spectroscopy, the predominant Mn oxides at all sites were poorly crystalline hexagonal birnessite, triclinic birnessite and todorokite. The surface morphology of the MnOx precipitates from all sites was coarse and “sponge-like” composed of nm-sized lathes and thin sheets. Based on scanning electron microscopy (SEM), MnOx precipitates were found in close proximity to both prokaryotic and eukaryotic organisms. The greatest removal efficiency of Mn(II) occurred at the one site with a higher pH in the bed and a higher influent total organic C (TOC) concentration (provided by an upstream wetland). Biological oxidation of Mn(II) driven by heterotrophic activity was most likely the predominant Mn removal mechanism in these systems. Influent water chemistry and Mn(II) oxidation kinetics affected the relative distribution of MnOx mineral assemblages in CMD treatment systems. 相似文献
235.
Upper mantle xenoliths from Wikieup, AZ, provide abundant evidence for magmatic modification of the uppermost mantle beneath
the Transition Zone between the Colorado Plateau and the southern Basin and Range province. Upper mantle lithologies in this
xenolith suite are represented by spinel peridotite, wehrlite, plagioclase peridotite, and Al-augite group pyroxenites. Isotopic
data for these xenoliths yield relatively uniform values and suggest a common petrogenesis. Al-augite-bearing gabbro and pyroxenite
xenoliths from this locality are interpreted to have formed by crystal fractionation processes from parent alkali basalts
similar to the Wikieup host basalt. Mineral and whole rock compositions show consistent trends of increasing incompatible
element contents (Fe, Al, Ca, Na, K, LIL, and LREE), and decreasing compatible element contents (Mg, Cr, Ni) from spinel peridotite
to wehrlite to plagioclase peridotite to the host basalt composition. These compositional trends are interpreted as resulting
from varying degrees of magma-mantle wall rock interaction as ascending mafic magmas infiltrated upper mantle peridotite.
Small degrees of melt infiltration resulted in slightly modified spinel peridotite compositions while moderate degrees metasomatized
spinel peridotite to wehrlite, and the highest degrees metasomatized it to plagioclase peridotite. Whole rock compositions
and clinopyroxene, plagioclase, and whole rock isotopic data suggest that the infiltrating magmas were the same as those from
which the gabbros and pyroxenites crystallized, and that they were alkalic in composition, similar to the Wikieup host alkali
olivine basalts. Relatively uniform 143Nd/144Nd for the mineral separates and whole rocks in spite of the significantly wide range in their 147Sm/144Nd (0.71–0.23 in clinopyroxene) suggests that the Wikieup xenoliths including gabbro, pyroxenite, peridotite, wehrlite, and
plagioclase peridotite, are all relatively young rocks formed or metasomatized by a relatively recent magmatic episode.
Received: 21 May 1996 / Accepted: 23 December 1996 相似文献
236.
This paper develops a simple bioeconomic model to investigate the economic and ecological issues associated with the commercial harvest of Pacific sardines relative to their value as forage for commercially, recreationally, and ecologically important predators in the California Current ecosystem. The model was used to evaluate how changes in the net per unit value of sardines, the net per unit value of sardine predators, and the transfer efficiency of predators affect the total net value of sardines, i.e. the net value of catches and the net value from sardine predation. Given recent market conditions for sardines and their commercial predators, and transfer efficiencies derived from predation data of the 1960s, it was found that the value of commercially caught predators and the efficiency by which they convert sardines to exploitable biomass were most important in determining the viability of the sardine fishery. The values assumed for predators that are not commercially caught were of no consequence under these conditions. Taking the value of sardines as forage into account does not necessarily mean an either-or situation for the fishery. As long as there is some measure of net value from the fishery and net value from predation, both benefit society at large. 相似文献
237.
Samuel J. Goldstein Jr. 《Celestial Mechanics and Dynamical Astronomy》1982,27(1):53-63
The solar tables of ibn Yunis and of King Alfonso, those of Kepler, of G. D. and J.-J. Cassini, and of Lalande are compared with Newcomb's theory of the Sun to determine the deceleration of the Earth's rotation. Comparisons of mean motion and of longitude lead to separate determinations. A value for the deceleration,
, assumed to be independent of time is obtained for the period — 146 through 1892. This result is based on the assumption that Newcomb's theory converts the Earth's orbital motion into a perfect clock, and the result is independent of lunar and tidal theory. The deceleration seems greater than that obtained from the literature for the tidal deceleration caused by the Moon. 相似文献
238.
Ore reserves forecasts are required to aid in investment decisions, mine design and valuation, short and long term production plans and proper and efficient mill design. In random multivariable fields with limited data and high levels of uncertainty, the kriged block estimates produce a smoothing effect resulting in underestimating high values and overestimating low values. The modified conditional simulation (MCS) methodology solves these problems by simulating the random field to preserve its mean and the variance structure. The simulation model is conditioned to reproduce the data at known sample points to minimize the variability between the simulated data and the true field data. In this study, the authors develop the MCS methodology to simulate ore reserve grades using the best linear unbiased estimation (BLUE) and the local average subdivision (LAS) techniques. The MCS methodology is applied to simulate block grades in a section of the Sabi Gold Project in Zimbabwe. The results are compared with the kriged estimates for this section. Analysis of the results shows that the MCS methodology reproduces the known sample grades with minimum estimation error of 0.001 while the estimation error associated with the kriged estimates is 1.104, a 100% efficiency of the MCS method over the kriging technique. 相似文献
239.
The D/H ratios of separated size fractions of clay minerals in two deep sea sediments taken from depths of 30 and 1100cm in a North Pacific Ocean core were measured to investigate the extent of hydrogen isotope exchange between detrital clay minerals and sea water. The D/H ratio of each size fraction of the shallower sample was compared with that of the corresponding size fraction of the deeper sample. No differences were detected between D/H ratios of corresponding size fractions from the two levels in the core except for the <0.1μm size fraction, which makes up only 5% of the sample. Even in this size fraction only about 8–28% D/H exchange is apparent. This is interpreted as indicating that no significant hydrogen isotope exchange between clay minerals and sea water has occurred during the past 2–3 Myr. Therefore information concerning the provenance and mode of formation of detrital clay minerals can be obtained from the D/H ratios of deep sea sediments younger than 2–3 Myr. 相似文献
240.
Leung CC Jefferson TA Hung SK Zheng GJ Yeung LW Richardson BJ Lam PK 《Marine pollution bulletin》2005,50(12):33-1719