Exact formulas for approximating variogram function integrals     

Mark R. Dunn  H. Dennis Tolley  J. Richard Alldredge 《Mathematical Geology》1980,12(6):577-588

The application of regionalized variables requires the estimation of the variogram function and the evaluation of its integral. By representing the variogram by a polygonal function the integral may be easily approximated by closed form representations of polygonal integrals. This approach provides a basis for more extensive statistical evaluation not evident in existing approximation methods. This paper provides the closed form representations for two-dimensional variogram functions whose domain is represented by a finite collection of rectangles.  相似文献   

Sources and sinks of nutrients in a New Zealand hill pasture catchment I. Stormflow generation     

James G. Cooke  Tony Dons 《水文研究》1988,2(2):109-122

The processes of stormflow generation were studied in a hill pasture catchment near Hamilton, New Zealand. Although rainfall was relatively evenly distributed throughout the year, stormflow was highly seasonal and over 65 per cent occurred during the winter. Three main processes contributing to stormflow were identified which could be related to soil type and physiographic position. On gleyed soils derived from rhyolitic colluvium, saturation overland flow was the dominant process. Hydrographs from ‘Whipkey’ throughflow troughs also indicated that there was a subsurface response (saturated wedge) from this soil type. On steeper convex slopes, more permeable soils were derived from weathered greywacke. The presence of ephemeral springs on the hillslopes and direct observation during storm events indicated that storm runoff was generated as return flow from this soil. It was noted that nitrate concentrations from subsurface sources were 5–10 times higher than surface runoff. This difference in concentration was utilized in a chemical mixing equation which partitioned stormflow sources. This was compared with the stormflow predicted from rain falling on to saturated areas. There was good agreement between the two models for winter-spring events with respect to the volumes of surface runoff predicted, however the saturated areas model underestimated total stormflow. The results of the study are briefly discussed in terms of the potential for water quality management.  相似文献   

AGRICULTURAL DROUGHT ON SOUTH-CENTRAL PACIFIC ISLANDS *     

Thomas W. Giambelluca  Dennis Nullet  Michael A. Nullet 《The Professional geographer》1988,40(4):404-415

A pilot study of spatial patterns of agricultural drought hazard in the south-central Pacific is presented. The durations of crop stress periods are estimated using a water balance approach. A rainfall approach is used to identify dry periods corresponding to different durations. Strong correlation between the results of the two methods indicates that monthly rainfall data are sufficient for estimating the patterns of agricultural drought hazard in the region. The simpler rainfall method is particularly useful for high islands where data required for the water balance approach are not sufficient to characterize the complex climatic patterns. Drought hazard is greatest in the eastern and southwestern parts of the study area. Great spatial variation in drought hazard is observed in a small area on the high islands of Western Samoa, where the range of values found within a few tens of kilometers is about the same as the range found across thousands of kilometers for low islands.  相似文献   

Meteor44 Video Meteor Photometry     

Wesley R. Swift  Robert M. Suggs  William J. Cooke 《Earth, Moon, and Planets》2004,95(1-4):533-540

Meteor44 is a software system developed at MSFC for the calibration and analysis of video meteor data. The photometric range of the (8 bit) video data is extended from a visual magnitude range of from 8 to 3 to from 8 to −8 for both meteors and stellar images using saturation compensation. Camera and lens specific saturation compensation coefficients are derived from artificial variable star laboratory measurements. Saturation compensation significantly increases the number of meteors with measured intensity and improves the estimation of meteoroid mass distribution. Astrometry is automated to determine each image's plate coefficient using appropriate star catalogs. The images are simultaneously intensity calibrated from the contained stars to determine the photon sensitivity and the saturation level referenced above the atmosphere. The camera's spectral response is used to compensate for stellar color index and typical meteor spectra in order to report meteor light curves in traditional visual magnitude units. Recent efforts include improved camera calibration procedures and long focal length "streak" meteor photometry. Meteor44 has been used to analyze data from the 2001, 2002 and 2003 MSFC Leonid observational campaigns as well as several lesser showers.  相似文献   

Scaling Properties of Biologically Active Scalar Concentration Fluctuations in the Atmospheric Surface Layer over a Managed Peatland     

Matteo Detto  Dennis Baldocchi  Gabriel G. Katul 《Boundary-Layer Meteorology》2010,136(3):407-430

The higher-order scalar concentration fluctuation properties are examined in the context of Monin–Obukhov similarity theory for a variety of greenhouse gases that have distinct and separate source/sink locations along an otherwise ideal micrometeorological field site. Air temperature and concentrations of water vapour, carbon dioxide and methane were measured at high frequency (10 Hz) above a flat and extensive peat-land soil in the San Joaquin–Sacramento Delta (California, USA) area, subjected to year-round grazing by beef cattle. Because of the heterogeneous distribution of the sources and sinks of CO₂ and especially CH₄ emitted by cattle, the scaling behaviour of the higher-order statistical properties diverged from predictions based on a balance between their production and dissipation rate terms, which can obtained for temperature and H₂O during stationary conditions. We identify and label these departures as ‘exogenous’ because they depend on heterogeneities and non-stationarities induced by boundary conditions on the flow. Spectral analysis revealed that the exogenous effects show their signatures in regions with frequencies lower than those associated with scalar vertical transport by turbulence, though the two regions may partially overlap in some cases. Cospectra of vertical fluxes appear less influenced by these exogenous effects because of the modulating role of the vertical velocity at low frequencies. Finally, under certain conditions, the presence of such exogenous factors in higher-order scalar fluctuation statistics may be ‘fingerprinted’ by a large storage term in the mean scalar budget.  相似文献   

European climate of the past 500 years based on documentary and instrumental data   总被引：1，自引：1，他引：0  

Rudolf Brázdil  Dennis Wheeler  Christian Pfister 《Climatic change》2010,101(1-2):1-6

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The meteorological framework and the cultural memory of three severe winter-storms in early eighteenth-century Europe     

Christian Pfister  Emmanuel Garnier  Maria-João Alcoforado  Dennis Wheeler  Jürg Luterbacher  Maria Fatima Nunes  João Paulo Taborda 《Climatic change》2010,101(1-2):281-310

Three violent eighteenth-century storms that ravaged the North Sea area (1703), western central Europe (1739) and Portugal (1739) are investigated from the point of view of their meteorological setting, their socio-economic impact, and whether and by what means they secured an enduring place in the cultural memory. The evidence draws on individual narrative sources such as chronicles and poems, and institutional sources such as ship’s logbooks and state-organised ‘windthrow’ inventories of tree loss. Each of the three storms had socio-economic impacts that could be described as ‘war-like’ in the damage caused to buildings and the destruction of forests. The “Great Storm” of December 1703 jeopardized English naval supremacy in the War of the Spanish Succession by sinking a number of Royal Navy ships and taking the life of more than 8000 seamen. In January 1739 two similarly destructive storms swept over mainland Europe. The cultural memory of the three events here considered was however strikingly different. The sequence of storms in January 1739 though being the most protracted of the last centuries, and well-chroniceled, did not persist in the collective memories of those in France, Switzerland and elsewhere who experienced them. Likewise, the “Great Storm” was quickly forgotten on the continent, whereas its memory remained deeply rooted in England through the writings of Defoe (1704). In Portugal the 1739 storm won a lasting place in the country’s cultural memory owing to two poems that it inspired. Furthermore, it was recorded in the Kingdom’s official newspaper, in the astronomical prognoses and in written records of the Old Regime’s cultural elite.  相似文献   

Hydrologic impacts of climate change on the Nile River Basin: implications of the 2007 IPCC scenarios   总被引：2，自引：1，他引：1  

Tazebe Beyene  Dennis P. Lettenmaier  Pavel Kabat 《Climatic change》2010,100(3-4):433-461

We assess the potential impacts of climate change on the hydrology and water resources of the Nile River basin using a macroscale hydrology model. Model inputs are bias corrected and spatially downscaled 21st Century simulations from 11 General Circulation Models (GCMs) and two global emissions scenarios (A2 and B1) archived from the 2007 IPCC Fourth Assessment Report (AR4). While all GCMs agree with respect to the direction of 21st Century temperature changes, there is considerable variability in the magnitude, direction, and seasonality of projected precipitation changes. Our simulations show that, averaged over all 11 GCMs, the Nile River is expected to experience increase in streamflow early in the study period (2010–2039), due to generally increased precipitation. Streamflow is expected to decline during mid- (2040–2069) and late (2070–2099) century as a result of both precipitation declines and increased evaporative demand. The predicted multimodel average streamflow at High Aswan Dam (HAD) as a percentage of historical (1950–1999) annual average are 111 (114), 92 (93) and 84 (87) for A2 (B1) global emissions scenarios. Implications of these streamflow changes on the water resources of the Nile River basin were analyzed by quantifying the annual hydropower production and irrigation water release at HAD. The long-term HAD release for irrigation increases early in the century to 106 (109)% of historical, and then decreases to 87 (89) and 86 (84)% of historical in Periods II and III, respectively, for the A2 (B1) global emissions scenarios. Egypt’s hydropower production from HAD will be above the mean annual average historical value of about 10,000 GWH for the early part of 21st century, and thereafter will generally follow the streamflow trend, however with large variability among GCMs. Agricultural water supplies will be negatively impacted, especially in the second half of the century.  相似文献   

Hydrocarbons generated by hydropyrolysis of suspended marine particulate organic matter: Relationship to the oceanography of the Black Sea and the Rhodes Gyre     

Yeşim Çoban-Yildiz  Alec F. Gaines  Pat E. Keating  Gordon D. Love  Dennis McLoughlin  Colin E. Snape 《Organic Geochemistry》2009,40(2):270-282

The suspended particulate organic matter, SPOM, in the autumnal Black Sea has been characterised using catalytic hydropyrolysis (HyPy) of the total (bound plus free) lipid material. The technique, which generates maximum yields of volatile products from sediments, kerogens and phytoplankton, was followed using gas chromatography and gas chromatography/mass spectrometry. The generated alkanes were dominated by n-C₁₈, hypothesised to arise predominantly from unsaturated C₁₈ fatty acids. Steranes were generated from reductive conversion of free and bound sterols. The generation of branched alkanes and especially of hopanes provided formal evidence for the participation of bacteria in the mineralisation of the SPOM. Whereas similar distributions of n-alkanes were generated from SPOM sampled from different depths of the comparatively well-stirred Rhodes Gyre (eastern Mediterranean), mineralisation of the SPOM at each depth of the central Black Sea produced characteristic changes in the composition and concentration of the HyPy products. Depth profiles of the n-alkanes generated from SPOM in the region of the Rim Current were affected by the local hydrography. Polynuclear aromatic hydrocarbons (PAHs) of anthropogenic origin were present in the surface waters of the central Black Sea. Some methyl benzenes, thiophenes and pyrroles were also generated.  相似文献   

Krieger’s conceptualization and measurement of discrimination and internalized oppression in studies of adverse health outcomes   总被引：1，自引：1，他引：0  

Eugenia Conde  Dennis M. Gorman 《GeoJournal》2009,74(2):131-142

Embodiment is a central concept in Krieger’s ecosocial theory, and is said to be of relevance to the understanding of the relationship between social conditions and a variety of adverse health outcomes. The most detailed empirical investigation of this in Krieger’s work is to be found in her studies of the relationship between racial discrimination and high blood pressure. Of especial relevance here is the idea of internalized oppression which is said to explain the observed association between self-reports of no racial discrimination and increased levels of blood pressure among working-class African Americans. Here we critically examine the empirical evidence pertaining to internalized oppression. Specifically, we focus on the measurement of the construct and the quality of the empirical evidence that has been presented in support of the hypothesis that there is an association between internalized oppression and adverse health outcomes. We argue that the validity of the concept has yet to be established and that the available data linking it to poor health outcomes are open to alternative explanations, notably measurement error and misclassification.

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Eugenia CondeEmail:

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