Cryologic continuum of a steep watershed          下载免费PDF全文

Benoit Turcotte  Brian Morse  François Anctil 《水文研究》2014,28(3):809-822

Ice processes taking place in steep channels are sensitive to the thermal and hydrological regimes of upstream reaches and tributaries as well as to the local channel morphology. This work presents freezeup, mid‐winter, and breakup data from four channels of increasing order located in a cold temperate watershed during the winter 2010–2011. From headwater channels to the main drainage system, water temperature, ice coverage, and ice processes are reported and related to weather conditions and to channel characteristics. Headwater channels only formed ephemeral ice features, and their water temperature reached as much as 4 °C in mid‐winter. On the other hand, larger channels formed impressively large ice dams, some of them reaching 2 m in height. The development of a suspended ice cover partially insulated the channels; as a result, water temperatures remained above 0 °C even for air temperatures well below freezing. This work presents steep channels ice processes that have not been described in previous publications. The concept of a watershed cryologic continuum (WCC) is developed from the data collected at each channel order. This concept emphasizes the feedback loops that exist between morphology, hydrology, heat, and ice processes in a given watershed and can lead to a better understanding of ice processes taking place at any channel location within that watershed. The WCC can also contribute in improving our understanding of the impacts of climate change on the cryologic and thermal regimes of steep channels. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

A new method to estimate the oxidation state of basaltic series from microprobe analyses     

Lydéric France  Benoit Ildefonse  Juergen Koepke  Florent Bech 《Journal of Volcanology and Geothermal Research》2010,189(3-4):340-346

The oxygen fugacity and therefore the iron redox state of a melt is known to have a strong influence on the liquid line of descent of magmas and thus on the composition of the coexisting melts and crystals. We present a new method to estimate this critical parameter from electron probe microanalyses of two of the most common minerals of basaltic series, plagioclase and clinopyroxene. This method is not based on stoichiometric calculations, but on the different partitioning behaviour of Fe³⁺ and Fe²⁺ between both minerals and a melt phase: plagioclase can incorporate more Fe³⁺ than Fe²⁺, while clinopyroxene can incorporate more Fe²⁺ than Fe³⁺. For example, the effect of oxidizing a partly molten basaltic system (Fe³⁺ is stabilized with respect to Fe²⁺) results in an increase of FeO_total in plagioclase, but a decrease in the associated clinopyroxene. We propose an equation, based on published partition coefficients, that allows estimating the redox state of a melt from these considerations. An application to a set of experimental and natural data attests the validity of the proposed model. The associated error can be calculated and is on average < 1 log unit of the prevailing oxygen fugacity.In order to reduce the number of different variables influencing the Fe²⁺/Fe³⁺ mineral/melt equilibrium, our model is restricted to basaltic series with SiO₂ < 60% that have crystallized at intermediate to low pressure (< 0.5 GPa) and under relatively oxidizing conditions (?FMQ > 0; where FMQ is the fayalite–magnetite–quartz oxygen buffer equilibrium), but it may be parameterized for other conditions. A spreadsheet is provided to assist the use of equations, and to perform the error propagation analysis.  相似文献   

Mineralogy, geochemistry and petrogenesis of the recent magmatic formations from Mbengwi, a continental sector of the Cameroon Volcanic Line (CVL), Central Africa     

Beno?t Joseph Mbassa  Emmanuel Njonfang  Mathieu Benoit  Pierre Kamgang  Michel Grégoire  Stephanie Duchene  Pierre Brunet  Bekoa Ateba  Félix M. Tchoua 《Mineralogy and Petrology》2012,106(3-4):217-242

The Mbengwi recent magmatic formations consist of volcanics and syenites belonging to the same magmatic episode. Lavas form a bimodal basanite-rhyolite alkaline series with a gap between 50 and 62?wt.% SiO₂. Mafic lavas (basanite-hawaiite) are sodic while felsic rocks (trachyte-rhyolite-syenites) are sodi-potassic, slightly metaluminous to peralkaline. The geochemical and isotopic characteristics (0.7031?<?(⁸⁷Sr/⁸⁶Sr)_initial?<?0.7043; 1.03?<?ε_Ndi?<?5.17) of these rocks are similar to those of other rocks from the CVL. The main differentiation process is fractional crystallization with two trends of fractionation. Their Rb/Sr isochron age of 28.2?Ma, almost similar to 27.40?±?0.6?Ma?K/Ar age obtained in a trachyte from neighboring Bamenda Mountains system, precludes any local age migration of an hypothetic hotspot. Mafic lavas have OIB features displaying an isotopic signature similar to that of HIMU mantle source different from FOZO known as source of most parental magmas along the CVL.  相似文献   

Predicted and observed magnetic signatures of martian (de)magnetized impact craters     

Benoit Langlais  Erwan Thébault 《Icarus》2011,212(2):568-578

The current morphology of the martian lithospheric magnetic field results from magnetization and demagnetization processes, both of which shaped the planet. The largest martian impact craters, Hellas, Argyre, Isidis and Utopia, are not associated with intense magnetic fields at spacecraft altitude. This is usually interpreted as locally non- or de-magnetized areas, as large impactors may have reset the magnetization of the pre-impact material. We study the effects of impacts on the magnetic field. First, a careful analysis is performed to compute the impact demagnetization effects. We assume that the pre-impact lithosphere acquired its magnetization while cooling in the presence of a global, centered and mainly dipolar magnetic field, and that the subsequent demagnetization is restricted to the excavation area created by large craters, between 50- and 500-km diameter. Depth-to-diameter ratio of the transient craters is set to 0.1, consistent with observed telluric bodies. Associated magnetic field is computed between 100- and 500-km altitude. For a single-impact event, the maximum magnetic field anomaly associated with a crater located over the magnetic pole is maximum above the crater. A 200-km diameter crater presents a close-to-1-nT magnetic field anomaly at 400-km altitude, while a 100-km diameter crater has a similar signature at 200-km altitude. Second, we statistically study the 400-km altitude Mars Global Surveyor magnetic measurements modelled locally over the visible impact craters. This approach offers a local estimate of the confidence to which the magnetic field can be computed from real measurements. We conclude that currently craters down to a diameter of 200 km can be characterized. There is a slight anti-correlation of −0.23 between magnetic field intensity and impact crater diameters, although we show that this result may be fortuitous. A complete low-altitude magnetic field mapping is needed. New data will allow predicted weak anomalies above craters to be better characterized, and will bring new constraints on the timing of the martian dynamo and on Mars’ evolution.  相似文献   

The Planck High Frequency Instrument, a third generation CMB experiment, and a full sky submillimeter survey     

J. M. Lamarre  J. L. Puget  F. Bouchet  P. A. R. Ade  A. Benoit  J. P. Bernard  J. Bock  P. De Bernardis  J. Charra  F. Couchot  J. Delabrouille  G. Efstathiou  M. Giard  G. Guyot  A. Lange  B. Maffei  A. Murphy  F. Pajot  M. Piat  I. Ristorcelli  D. Santos  R. Sudiwala  J. F. Sygnet  J. P. Torre  V. Yurchenko  D. Yvon 《New Astronomy Reviews》2003,47(11-12):1017

The High Frequency Instrument (HFI) of Planck is the most sensitive CMB experiment ever planned. Statistical fluctuations (photon noise) of the CMB itself will be the major limitation to the sensitivity of the CMB channels. Higher frequency channels will measure galactic foregrounds. Together with the Low Frequency Instrument, this will make a unique tool to measure the full sky and to separate the various components of its spectrum. Measurement of the polarization of these various components will give a new picture of the CMB. In addition, HFI will provide the scientific community with new full sky maps of intensity and polarization at six frequencies, with unprecedented angular resolution and sensitivity. This paper describes the logics that prevailed to define the HFI and the performances expected from this instrument. It details several features of the HFI design that has not been published up to now.  相似文献   

Sensitivity experiments for polar low forecasting with the CMC mesoscale finite‐element model     

Michel Roch  Robert Benoit  Neil Parker 《大气与海洋》2013,51(3):381-419

Abstract

High‐resolution versions of the Canadian operational regional finite‐element model (RFE) have been developed to assess their potential in simulating mesoscale, difficult‐to‐forecast and potentially dangerous weather systems commonly referred to as polar lows. The operational (1989) 100‐km version and a 50‐km version of the model have been run for two different polar low cases: one over Hudson Bay and one over Davis Strait. More integrations have also been performed on the Hudson Bay event both at 50 and 25 km to assess the model sensitivity to ice cover. As expected, the reduction in spatial truncation errors provided by the increase in resolution results in a better simulation of the systems. Moreover, when run at higher resolutions the model shows a significant sensitivity to ice cover. The results of the ice‐cover experiments also put into perspective the interaction between the heat and moisture fluxes at the surface, the low‐level wind structure, and the relation of these to the development of the polar low. This study suggests that the improved forecast accuracy obtained from increased resolution is limited by the correctness of the analysis of the ice cover, which acts as a stationary forcing for the entire forecast period.  相似文献   

Impact of soil map specifications for European climate simulations     

Benoit P. Guillod  Edouard L. Davin  Christine Kündig  Gerhard Smiatek  Sonia I. Seneviratne 《Climate Dynamics》2013,40(1-2):123-141

Soil physical characteristics can influence terrestrial hydrology and the energy balance and may thus affect land–atmosphere exchanges. However, only few studies have investigated the importance of soil textures for climate. In this study, we examine the impact of soil texture specification in a regional climate model. We perform climate simulations over Europe using soil maps derived from two different sources: the soil map of the world from the Food and Agricultural Organization and the European Soil Database from the European Commission Joint Research Center. These simulations highlight the importance of the specified soil texture in summer, with differences of up to 2 °C in mean 2-m temperature and 20 % in precipitation resulting from changes in the partitioning of energy at the land surface into sensible and latent heat flux. Furthermore, we perform additional simulations where individual soil parameters are perturbed in order to understand their role for summer climate. These simulations highlight the importance of the vertical profile of soil moisture for evapotranspiration. Parameters affecting the latter are hydraulic diffusivity parameters, field capacity and plant wilting point. Our study highlights the importance of soil properties for climate simulations. Given the uncertainty associated with the geographical distribution of soil texture and the resulting differences between maps from different sources, efforts to improve existing databases are needed. In addition, climate models would benefit from tackling unresolved issues in land-surface modeling related to the high spatial variability in soil parameters, both horizontally and vertically, and to limitations of the concept of soil textural class.  相似文献   

Assessment of the Design of an Experimental Cover with Capillary Barrier Effect Using 4 Years of Field Data     

Amir M. Abdolahzadeh  Benoit Lacroix Vachon  Alexandre R. Cabral 《Geotechnical and Geological Engineering》2011,29(5):783-802

One important step in the design of inclined covers with capillary barrier effect (CCBE) is the determination of the water diversion length (DL). Numerical simulations can predict the DL more precisely than steady-state analytical solutions. Nevertheless, as simplified methods have always been part of engineering design, the application of analytical solutions with conservative boundary conditions, may allow engineers to make reasonable predictions, particularly during the pre-feasibility stage of a project. In this study, a CCBE was designed, constructed and instrumented at the Saint-Tite-des-Caps landfill, Quebec, Canada. This CCBE included a seepage control layer superimposing a sand-gravel capillary barrier. The seepage control layer was made up of deinking by-products (DBP), an industrial by-product that was previously disposed of as waste. The capillary barrier was designed using an adaptation of the Ross analytical solution and the scenario considered was that of steady-state flow during constant seepage flow applied uniformly at the top of the sand-gravel capillary barrier. Although these conditions appear simplistic, they were deemed reasonable because placement of the seepage control layer on the top of the capillary barrier led to very low suctions at the interface, thereby allowing uniform downward seepage rates, limited by the saturated hydraulic conductivity of the DBP. In this paper, a discussion about the behaviour of the cover system based on 4 years of field data from several instruments is presented. The challenge of using DBP, more precisely the settlement of the DBP layer and its impact on k _sat , is also assessed. The DL was reassessed considering the new k _sat . A discussion on the validity of employing analytical solutions to determine DL is also presented. This paper illustrates how certain variables affect the design of inclined CCBEs that include a highly compressible material as seepage control layer.  相似文献   

The natural thermoluminescence of meteorites VI: Carbon-14, thermoluminescence and the terrestrial ages of meteorites     

P. H. Benoit  A. J. T. Jull  S. W. S. McKeever  D. W. G. Sears 《Meteoritics & planetary science》1993,28(2):196-203

Abstract Research on meteorite finds, especially those from the Antarctic and from desert regions in Australia, Africa, and America, has become increasingly important, notably in studies of possible changes in the nature of the meteorite flux in the past. One important piece of information needed in the study of such meteorites is their terrestrial age which can be determined using a variety of methods, including ¹⁴C, ³⁶Cl, and ⁸¹Kr. Natural thermoluminescence (TL) levels in meteorites can also be used as an indicator of terrestrial age. In this paper, we compare ¹⁴C-determined terrestrial ages with natural TL levels in finds from the Prairie States (central United States), a group of finds from Roosevelt County (New Mexico, USA), and a group from the Sahara Desert. We find that, in general, the natural TL data are compatible with the ¹⁴C-derived terrestrial ages using a 20 °C TL decay curve for the Prairie States and Roosevelt County and a 30 °C decay curve for the Saharan meteorites. We also present TL data for a group of meteorites from the Sahara desert which has not been studied using cosmogenic radionuclides. Within these data there are distinct terrestrial age clusters which probably reflect changes in meteorite preservation efficiency over ～ 15, 000 years in the region.  相似文献   

Properties of chondrules in EL3 chondrites,comparison with EH3 chondrites,and the implications for the formation of enstatite chondrites     

D. M. Schneider  S. J. K. Symes  P. H. Benoit  D. W. G. Sears 《Meteoritics & planetary science》2002,37(10):1401-1416

Abstract— The study of chondrules provides information about processes occurring in the early solar system. In order to ascertain to what extent these processes played a role in determining the properties of the enstatite chondrites, the physical and chemical properties of chondrules from three EL3 chondrites and three EH3 chondrites have been examined by optical, cathodoluminescence (CL), and electron microprobe techniques. Properties examined include size, texture, CL, and composition of both individual phases and bulk chondrules. The textures, distribution of textures, and composition of silicates of the EL3 chondrules resemble those of EH3 chondrules. However, the chondrules from the two classes differ in that (1) the size distribution of the EL chondrules is skewed to larger values than EH chondrules, (2) the enstatite in EL chondrules displays varying shades of red CL due to the presence of fine‐grained sulfides and metal in the silicates, and (3) the mesostasis of EH chondrules is enriched in Na relative to that of EL chondrules. The similarities between the chondrules of the two classes suggest similar precursor materials, while the differences suggest that there was not a single reservoir of meteoritic chondrules, but that their origin was fairly local. The differences in the size distribution of chondrules in EH and EL chondrites may be explained by aerodynamic and gravitational sorting during accumulation of the meteoric material, while differences in CL and mesostasis properties may reflect differences in formation conditions and cooling rate following chondrule formation. We argue that our observations are consistent with the formation of enstatite chondrites in a thick dynamic regolith on their parent body.  相似文献