Climate model dependence and the replicate Earth paradigm   总被引：1，自引：1，他引：0  

Craig H. Bishop  Gab Abramowitz 《Climate Dynamics》2013,41(3-4):885-900

Multi-model ensembles are commonly used in climate prediction to create a set of independent estimates, and so better gauge the likelihood of particular outcomes and better quantify prediction uncertainty. Yet researchers share literature, datasets and model code—to what extent do different simulations constitute independent estimates? What is the relationship between model performance and independence? We show that error correlation provides a natural empirical basis for defining model dependence and derive a weighting strategy that accounts for dependence in experiments where the multi-model mean would otherwise be used. We introduce the “replicate Earth” ensemble interpretation framework, based on theoretically derived statistical relationships between ensembles of perfect models (replicate Earths) and observations. We transform an ensemble of (imperfect) climate projections into an ensemble whose mean and variance have the same statistical relationship to observations as an ensemble of replicate Earths. The approach can be used with multi-model ensembles that have varying numbers of simulations from different models, accounting for model dependence. We use HadCRUT3 data and the CMIP3 models to show that in out of sample tests, the transformed ensemble has an ensemble mean with significantly lower error and much flatter rank frequency histograms than the original ensemble.  相似文献   

Paleoecological evidence of major declines in total organic carbon concentrations since the nineteenth century in four nemoboreal lakes     

Laura?CunninghamEmail author  Kevin?Bishop  Eva?Mett?vainio  Peter?Rosén 《Journal of Paleolimnology》2011,45(4):507-518

A decade of widespread increases in surface water concentrations of total organic carbon (TOC) in some regions has raised questions about longer term patterns in this important constituent of water chemistry. This study uses near-infrared spectroscopy (NIRS) to infer lake water TOC far beyond the decade or two of observational data generally available. An expanded calibration dataset of 140 lakes across Sweden covering a TOC gradient from 0.7 to 24.7 mg L⁻¹ was used to establish a relationship between the NIRS signal from surface sediments (0–0.5 cm) and the TOC concentration of the water mass. Internal cross-validation of the model resulted in an R ² of 0.72 with a root mean squared error of calibration (RMSECV) of 2.6 mg L⁻¹. The TOC concentrations reconstructed from surface sediments in four Swedish lakes were typically within the range of concentrations observed in the monitoring data during the period represented by each sediment layer. TOC reconstructions from the full sediment cores of four lakes indicated that TOC concentrations were approximately twice as high a century ago.  相似文献   

Interpreting luminescence data from a portable OSL reader: three case studies in fluvial settings     

Esperanza Muñoz‐Salinas  Paul Bishop  David CW Sanderson  Jose‐Juan Zamorano 《地球表面变化过程与地形》2011,36(5):651-660

Optically stimulated luminescence (OSL) is a technique that has been applied from the mid‐1980s, mainly for sediment dating. The OSL technique is based on sample stimulation by light to determine the luminescence signal that is stored in the crystal lattices of sediment grains after deposition, burial by later sediment and subsequent exposure to ionizing radiation from radioactive elements in the surrounding sediment. In such sediment dating, two parameters are required: the equivalent dose (i.e. the luminescence signal stored in the grains), and the dose rate (i.e. the ionizing energy from α, β and γ radiation emitted by naturally occurring radioisotopes in the deposit, plus the effects of cosmic radiation). In this research, the OSL technique is not used for dating. The study goal is to analyse only the luminescence signals (the total photon counts) in polymineral samples obtained after light stimulation in the blue (BLSL) and infrared (IRSL) wavelengths using a portable OSL reader designed and built at the Scottish Universities Environmental Research Centre (SUERC). Three fluvial case studies – from Cambodia, Australia and Mexico – are used to illustrate the geomorphological interpretations possible with the portable OSL reader data from sediments resulting from a range of different depositional processes. The case studies show that aspects of sediment's transport and depositional processes can be inferred from the portable OSL reader data, providing valuable insights into geomorphological history. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Development and testing of a coupled ocean–atmosphere mesoscale ensemble prediction system     

Teddy R. Holt  James A. Cummings  Craig H. Bishop  James D. Doyle  Xiaodong Hong  Sue Chen  Yi Jin 《Ocean Dynamics》2011,61(11):1937-1954

A coupled ocean–atmosphere mesoscale ensemble prediction system has been developed by the Naval Research Laboratory. This paper describes the components and implementation of the system and presents baseline results from coupled ensemble simulations for two tropical cyclones. The system is designed to take into account major sources of uncertainty in: (1) non-deterministic dynamics, (2) model error, and (3) initial states. The purpose of the system is to provide mesoscale ensemble forecasts for use in probabilistic products, such as reliability and frequency of occurrence, and in risk management applications. The system components include COAMPS® (Coupled Ocean/Atmosphere Mesoscale Prediction System) and NCOM (Navy Coastal Ocean Model) for atmosphere and ocean forecasting and NAVDAS (NRL Atmospheric Variational Data Assimilation System) and NCODA (Navy Coupled Ocean Data Assimilation) for atmosphere and ocean data assimilation. NAVDAS and NCODA are 3D-variational (3DVAR) analysis schemes. The ensembles are generated using separate applications of the Ensemble Transform (ET) technique in both the atmosphere (for moving or non-moving nests) and the ocean. The atmospheric ET is computed using wind, temperature, and moisture variables, while the oceanographic ET is derived from ocean current, temperature, and salinity variables. Estimates of analysis error covariance, which is used as a constraint in the ET, are provided by the ocean and atmosphere 3DVAR assimilation systems. The newly developed system has been successfully tested for a variety of configurations, including differing model resolution, number of members, forecast length, and moving and fixed nest options. Results from relatively coarse resolution (～27-km) ensemble simulations of Hurricanes Hanna and Ike demonstrate that the ensemble can provide valuable uncertainty information about the storm track and intensity, though the ensemble mean provides only a small amount of improved predictive skill compared to the deterministic control member.  相似文献   

Reflectance spectroscopy and geochemical analyses of Lake Hoare sediments, Antarctica: implications for remote sensing of the Earth and Mars     

Bishop JL  Koeberl C  Kralik C  Fröschl H  Englert PA  Andersen DW  Pieters CM  Wharton RA 《Geochimica et cosmochimica acta》1996,60(5):765-785

Visible to infrared reflectance spectroscopic analyses (0.3-25 micromoles) have been performed on sediments from the Dry Valleys region of Antarctica. Sample characterization for these sediments includes extensive geochemical analyses and X-ray diffraction (XRD). The reflectance spectra and XRD indicate major amounts of quartz, feldspar, and pyroxene in these samples and lesser amounts of carbonate, mica, chlorite, amphibole, illite, smectite, and organic matter. Calcite is the primary form of carbonate present in these Lake Hoare sediments based on the elemental abundances and spectroscopic features. The particle size distribution of the major and secondary components influences their detection in mixtures and this sensitivity to particle size is manifested differently in the "volume scattering" and "surface scattering" infrared regions. The Christiansen feature lies between these two spectral regimes and is influenced by the spectral properties of both regions. For these mixtures the Christiansen feature was found to be dependent on physical parameters, such as particle size and sample texture, as well as the mineralogy. Semiquantitative spectroscopic detection of calcite and organic material has been tested in these quartz- and feldspar-rich sediments. The relative spectral band depths due to organics and calcite correlate in general with the wt% C from organic matter and carbonate. The amounts of organic matter and carbonate present correlate with high Br and U abundances and high Ca and Sr abundances, respectively. Variation in the elemental abundances was overall minimal, which is consistent with a common sedimentary origin for the forty-two samples studied here from Lake Hoare.  相似文献   

Urban Ground-Water Pollution: A Case Study from Coventry, United Kingdom   总被引：1，自引：0，他引：1  

M. M. Nazari  M. W. Burston  P. K. Bishop  D. N. Lerner 《Ground water》1993,31(3):417-424

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Geophysical properties of zinc‐bearing deposits     

J. R. Bishop  D. W. Emerson 《Australian Journal of Earth Sciences》2013,60(3):311-328

At present, most, if not all zinc is being produced from the mineral sphalerite. With the exception of its piezoelectricity and in some cases its density, sphalerite has no salient physical properties to routinely allow its direct detection by geophysical methods. Although the mineral usually occurs with other sulfides, which do respond to various geophysical techniques, detection of zinc‐bearing deposits is often difficult. In this paper, physical property measurements from numerous, mainly Australian, deposits are presented, together with examples from various geophysical surveys. The results are used to suggest the most effective geophysical technique for the direct detection of the different types of zinc‐bearing deposits. Induced polarisation is probably the most effective technique for unmetamorphosed sediment‐hosted deposits and for carbonate‐hosted deposits, whereas electromagnetics is usually the most appropriate method to use for volcanic‐hosted deposits and for sediment‐hosted deposits that have been strongly metamorphosed. Magnetics is the best technique for skarn and ‘Cobar‐style’ deposits. However, it must be emphasised that usually more than one geophysical technique is required before a prospect can be considered to have been thoroughly explored.  相似文献   

Address databases for national SDI: Comparing the novel data grid approach to data harvesting and federated databases     

Serena Coetzee  Judith Bishop 《International journal of geographical information science》2013,27(9):1179-1209

The original purpose of addresses was to enable the correct and unambiguous delivery of postal mail. The advent of computers and more specifically geographic information systems (GIS) opened up a whole new range of possibilities for the use of addresses, such as routing and vehicle navigation, spatial demographic analysis, geo‐marketing, and service placement and delivery. Such functionality requires a database which can store and access spatial data effectively. In this paper we present address databases and justify the need for national address databases. We describe models used for national address databases, and present our evaluation framework for an address database at a national level within the context of a spatial data infrastructure (SDI). The models of data harvesting, federated databases and data grids are analyzed and evaluated according to our novel framework, and we show that the data grid model has some unique features that make it attractive for a national address database in an environment where centralized control and/or coordination is difficult or undesirable.  相似文献   

Resolving the Double Paradox of rapidly mobilized old water with highly variable responses in runoff chemistry   总被引：1，自引：0，他引：1  

Kevin Bishop  Jan Seibert  Stephan Khler  Hjalmar Laudon 《水文研究》2004,18(1):185-189

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Estimating quartz fabrics from piezoelectric measurements     

J. R. Bishop 《Mathematical Geology》1981,13(4):261-289

An aggregate of piezoelectric minerals may itself be piezoelectric if the minerals are suitably aligned. Thus quartz-bearing rocks may be piezoelectric, since quartz is one such mineral. It has been shown that some rocks do possess this effect, termed a piezoelectric fabric (Bishop, 1981). The type of piezoelectric fabric may be determined by matching experimental data to theoretical models of piezoelectric fabrics. These theoretical models of pure quartz aggregates are derived by considering the symmetry of the preferred crystallographic directions of the aggregate grains. From the symmetry, the piezoelectric matrix of the model may be determined. The best-fitting model and the orientation of its fabric is obtained by equating the experimental data to each model in turn. For each model, the best fitting fabric orientation is determined by using an inversion routine. If the experimental data are due to a piezoelectric fabric and not to some random or nonpolar distribution of grains, the fabric type (c-axis point maximum or large-circle girdle) and its orientation with respect to the specimen may be determined. The positions and polarities of the quartz a-axes are also specified. A statistical examination of results from a quartz-mylonite shows that the problem of piezoelectric model fitting is well posed, in that the Eulerian angles that specify the fabric orientation are fairly independent important parameters and a sufficiently close fit of the model to the data can be obtained to determine the fabric.  相似文献