Do paleoclimate proxies agree? A test comparing 19 late Holocene climate and sea‐ice reconstructions from Icelandic marine and lake sediments     

Yarrow Axford  Camilla S. Andresen  John T. Andrews  Simon T. Belt  Áslaug Geirsdóttir  Guillaume Massé  Gifford H. Miller  Sædís Ólafsdóttir  Lindsay L. Vare 《第四纪科学杂志》2011,26(6):645-656

Geochemical, mineralogical and biological indicators preserved in sediments are widely used to reconstruct past climate change, but proxies differ in the degree to which their utility as climate indicators has been validated via laboratory experiments, modern spatial calibrations, or down‐core comparisons with instrumental climate data. Multi‐proxy studies provide another means of evaluating interpretations of proxies. This paper presents a multi‐proxy assessment comparing 19 sub‐centennially resolved late Holocene proxy records, covering the period 300–1900 AD, from seven Icelandic marine and lacustrine core sites. We employ simple statistical comparisons between proxy reconstructions to evaluate their correlations over time and, ultimately, their utility as proxies for regional climate. Proxies examined include oxygen isotopic composition of benthic and planktonic foraminifera, abundance of the sea‐ice biomarker IP₂₅, allochthonous quartz in marine sediments (a proxy for drift ice around Iceland), marine carbonate abundance, total organic carbon concentration, chironomid assemblages, lacustrine biogenic silica and carbon/nitrogen ratios in lake sediments. Most of the examined proxy records, including temperature and sea‐ice proxies, correlate strongly with each other over multi‐centennial timescales, and thus do appear to record changes in regional climate. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Internal testing of a numerical model of hillslope–channel coupling using laboratory flume experiments     

Katerina Michaelides  John Wainwright 《水文研究》2008,22(13):2274-2291

The numerical model COUP 2D simulates the hydrological coupling between hillslopes and the river channel during a rainfall event. In order to test the numerical model, a 1:100 scaled laboratory flume which was modified to incorporate lateral hillslope elements, was used to run a series of experiments in which hillslope angle, channel angle, hillslope discharge and channel discharge were the varying parameters. Overall, there were 18 different experimental configurations with three replicates carried out for each condition, leading to a total of 54 experiments. These conditions were then used to parameterize and run COUP 2D. Internal model outputs of flow depth and flow velocity at four cross‐sections in the channel were compared to the measurements made in the physical model for the same parameter conditions. Statistical comparisons of the measured and modelled data were carried out for each experiment and across all experiments, using two goodness‐of‐fit measures—root mean square error and Nash–Sutcliffe coefficient of efficiency—in order to assess the performance of the model over an entire simulation as well as over all the simulations. The main effects on the goodness‐of‐fit measures for flow depth of each experimental variable, as well as the interactions between variables, were evaluated using statistical modelling. The results show that the model captures flow‐depth variations in response to changing channel and hillslope parameters. Statistical modelling suggests that the main effects on model error are cross‐section position, channel angle and channel discharge. Significant interactions also occur between all the channel variables and between the channel variables and hillslope discharge. The results of the testing procedure have significant implications for the consideration of different model components and for the interaction between data‐ and model evaluation. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Report on IAU colloquium no. 39 “the relationships of comets,minor planets and meteorites”     

John R. Dickel 《Icarus》1977,32(2):251-254

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The relationship of wind stress to heat flux divergence of Texas-Louisiana shelf waters     

Paul C. Etter  William F. Ulm  John D. Cochrane 《Continental Shelf Research》1985,4(5):547-552

Monthly, multi-annual mean heat budgets are calculated for waters overlying the Texas-Louisiana shelf. Heat storage rates are calculated on the basis of a volumetric temperature-salinity census; unpublished data from Bunker are consulted to determine surface heat exchanges. Monthly heat flux divergences, calculated as residuals in the heat budget equation, show divergence of heat during the months of June and July, the upwelling season for much of the Texas-Louisiana coast, and convergence of heat during the rest of the year when winds conducive to downwelling prevail.  相似文献   

Analyzing Radar Meteor Trail Echoes using the Fresnel Transform Technique: A Signal Processing Viewpoint     

Arnab Roy  John F. Doherty  John D. Mathews 《Earth, Moon, and Planets》2007,101(1-2):27-39

Several techniques have been proposed for measuring speeds of meteoroids observed using radars. A recent technique involves the use of Fresnel transforms to accurately determine the speed of a meteoroid producing the trail. We follow a numerical modeling approach to analyze this technique in detail. Our studies indicate that high sensitivity to background noise levels might be a possible shortcoming of the Fresnel transform method. A matched filtering approach is presented as an alternative to alleviate this sensitivity to the noise problem. Performance of the two techniques is compared using numerical modeling and data from a 30 MHz radar.  相似文献   

Geographers,Maps, And Campus Map Collections     

John V. Bergen 《The Professional geographer》1972,24(4):310-316

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Sedimentological,geomorphological and dynamic context of debris-mantled glaciers,Mount Everest (Sagarmatha) region,Nepal     

Michael J. Hambrey  Duncan J. Quincey  Neil F. Glasser  John M. Reynolds  Shaun J. Richardson  Samuel Clemmens 《Quaternary Science Reviews》2009,28(11-12):1084

This paper presents the sediment, landform and dynamic context of four avalanche-fed valley glaciers (Khumbu, Imja, Lhotse and Chukhung) in the Mount Everest (Sagarmatha) region of Nepal. All four glaciers have a mantle of debris dominated by sandy boulder-gravel that suppresses melting to an increasing degree towards the snout, leading to a progressive reduction in the overall slope of their longitudinal profile. Prominent lateral–terminal moraine complexes, also comprising sandy bouldergravel, enclose the glaciers. These terminal moraines originally grew by accretion of multiple sedimentary facies of basal glacial and supraglacial origin, probably by folding and thrusting when the glaciers were more dynamic during the Little Ice Age. The four glaciers are in various stages of recession, and demonstrate a range of scenarios from down-wasting of the glacier tongue, through morainedammed lake development, to post-moraine-dam breaching. Khumbu Glacier is at the earliest stage of supraglacial pond formation and shows no sign yet of developing a major lake, although one is likely to develop behind its >250 m high composite terminal moraine. Imja Glacier terminates in a substantial body of water behind a partially ice-cored moraine dam (as determined from geophysical surveys), but morphologically appears unlikely to be an immediate threat. Chukhung Glacier already has a breached moraine and a connected debris fan, and therefore no longer poses a threat. Lhotse Glacier has an inclined, free-draining tongue that precludes hazardous lake development. From the data assembled, a conceptual model, applicable to other Himalayan glaciers, is proposed to explain the development of large, lateral-terminal moraine complexes and associated potentially hazardous moraine dams. – 2008 Elsevier Ltd. All rights reserved.  相似文献   

Bedrock aquifers and population growth in the Denver Basin, Colorado, USA     

John E. Moore Robert G. Raynoldse Marieke Dechesne 《《幕》》2007,30(2):115-118

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The zoo hypothesis     

John A. Ball 《Icarus》1973,19(3):347-349

Extraterrestrial intelligent life may be almost ubiquitous. The apparent failure of such life to interact with us may be understood in terms of the hypothesis that they have set us aside as part of a wilderness area or zoo.  相似文献   

grommet: an N-body code for high-resolution simulations of individual galaxies     

John Magorrian 《Monthly notices of the Royal Astronomical Society》2007,381(4):1663-1671

This paper presents a fast, economical particle-multiple-mesh N -body code optimized for large- N modelling of collisionless dynamical processes, such as black hole wandering or bar–halo interactions, occurring within isolated galaxies. The code has been specially designed to conserve linear momentum. Despite this, it also has variable softening and an efficient block-time-step scheme: the force between any pair of particles is calculated using the finest mesh that encloses them both (respecting Newton's third law) and is updated only on the longest time-step of the two (which conserves momentum). For realistic galaxy models with   N ≳ 10⁶  , it is faster than the fastest comparable tree code by factors ranging from ∼2 (using single time-steps) to ∼10 (multiple time-steps in a concentrated galaxy).  相似文献