New initiative of ‘Invited peer-reviewed papers’ launched     

Kamlesh Lulla  M. Duane Nellis  Brad Rundquist 《国际地球制图》2013,28(6)

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Effect of rapidly changing river stage on uranium flux through the hyporheic zone   总被引：2，自引：1，他引：1  

Fritz BG  Arntzen EV 《Ground water》2007,45(6):753-760

Measurement of ground water/surface water interaction within the hyporheic zone is increasingly recognized as an important aspect of subsurface contaminant fate and transport. Understanding the interaction between ground water and surface water is critical in developing a complete conceptual model of contaminant transport through the hyporheic zone. At the Hanford Site near Richland, Washington, ground water contaminated with uranium discharges to the Columbia River through the hyporheic zone. Ground water flux varies according to changes in hydraulic gradient caused by fluctuating river stage, which changes in response to operation of dams on the Columbia River. Piezometers and continuous water quality monitoring probes were installed in the hyporheic zone to provide long-term, high-frequency measurement of hydraulic gradient and estimated uranium concentrations. Subsequently, the flux of water and uranium was calculated for each half-hour time period over a 15-month study period. In addition, measurement of water levels in the near-shore unconfined aquifer enhanced the understanding of the relationship between river stage, aquifer elevation, and uranium flux. Changing river stage resulted in fluctuating hydraulic gradient within the hyporheic zone. Further, influx of river water caused lower uranium concentrations as a result of dilution. The methods employed in this study provide a better understanding of the interaction between surface and ground water in a situation with a dynamically varying vertical hydraulic gradient and illustrate how the combination of relatively standard methods can be used to derive an accurate estimation of water and contaminant flux through the hyporheic zone.  相似文献   

Latitudinal variations in Titan’s methane and haze from Cassini VIMS observations     

Paulo F. Penteado  Caitlin A. Griffith  Steffi Engel  Lyn Doose  Robert H. Brown  Roger Clark  Christophe Sotin 《Icarus》2010,206(1):352-365

We analyze observations taken with Cassini’s Visual and Infrared Mapping Spectrometer (VIMS), to determine the current methane and haze latitudinal distribution between 60°S and 40°N. The methane variation was measured primarily from its absorption band at 0.61 μm, which is optically thin enough to be sensitive to the methane abundance at 20-50 km altitude. Haze characteristics were determined from Titan’s 0.4-1.6 μm spectra, which sample Titan’s atmosphere from the surface to 200 km altitude. Radiative transfer models based on the haze properties and methane absorption profiles at the Huygens site reproduced the observed VIMS spectra and allowed us to retrieve latitude variations in the methane abundance and haze. We find the haze variations can be reproduced by varying only the density and single scattering albedo above 80 km altitude. There is an ambiguity between methane abundance and haze optical depth, because higher haze optical depth causes shallower methane bands; thus a family of solutions is allowed by the data. We find that haze variations alone, with a constant methane abundance, can reproduce the spatial variation in the methane bands if the haze density increases by 60% between 20°S and 10°S (roughly the sub-solar latitude) and single scattering absorption increases by 20% between 60°S and 40°N. On the other hand, a higher abundance of methane between 20 and 50 km in the summer hemisphere, as much as two times that of the winter hemisphere, is also possible, if the haze variations are minimized. The range of possible methane variations between 27°S and 19°N is consistent with condensation as a result of temperature variations of 0-1.5 K at 20-30 km. Our analysis indicates that the latitudinal variations in Titan’s visible to near-IR albedo, the north/south asymmetry (NSA), result primarily from variations in the thickness of the darker haze layer, detected by Huygens DISR, above 80 km altitude. If we assume little to no latitudinal methane variations we can reproduce the NSA wavelength signatures with the derived haze characteristics. We calculate the solar heating rate as a function of latitude and derive variations of ∼10-15% near the sub-solar latitude resulting from the NSA. Most of the latitudinal variations in the heating rate stem from changes in solar zenith angle rather than compositional variations.  相似文献   

Titan’s vertical aerosol structure at the Huygens landing site: Constraints on particle size,density, charge,and refractive index     

P. Lavvas  R.V. Yelle  C.A. Griffith 《Icarus》2010,210(2):832-842

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Extrasolar planets around HD 196050, HD 216437 and HD 160691     

Hugh R. A. Jones  R. Paul Butler  Geoffrey W. Marcy  Chris G. Tinney  Alan J. Penny  Chris McCarthy  Brad D. Carter 《Monthly notices of the Royal Astronomical Society》2002,337(4):1170-1178

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The distance to Supernova 1998aq in NGC 3982     

Peter B. Stetson †  Brad K. Gibson 《Monthly notices of the Royal Astronomical Society》2001,328(1):L1-L4

We use the preliminary results of a new survey of radio sources made using the Ryle Telescope at 15.2 GHz, to estimate the impact of foreground sources on cm-wave cosmic microwave background (CMB) images. This is the highest frequency survey that is relevant to the issue of radio source contamination in CMB experiments. The differential source count of the 66 sources found in 63 deg² is     , from ≈20 to ≈500 mJy. Extrapolating this to 34 GHz (where many cm-wave CMB experiments operate) gives an estimated temperature contribution of sources     in a CMB image, with a beam corresponding to multipole     . A means of source subtraction is evidently necessary, otherwise the signal-to-noise ratio in CMB images will be limited to 4 or 5, becoming worse at higher resolution. We compare the population of sources observed in this new survey to that predicted by extrapolation from lower frequency surveys, finding that source flux densities, and indeed the existence of many sources, cannot be determined by extrapolation.  相似文献   

Energy Policy in Australia: A comparison of environmental considerations in New South Wales and Victoria     

Brad Jessup  David Mercer 《The Australian geographer》2001,32(1):7-28

World-wide, people and governments are gradually becoming more aware of the potential environmental, economic and health effects of climate change and the need for governments to take action to mitigate such impacts. This was emphasised by the creation of the United Nations Framework Convention on Climate Change (UNFCCC), signed at the Rio Earth Summit in 1992. There has been much discussion on the greenhouse policy response of the commonwealth government of Australia, especially its stance taken at Kyoto in December 1997. Despite the recent nationalisation of Australia's state energy markets, due to Australia's federal political structure, much of the policy responsibility for energy and environmental issues rests with the states. Given these circumstances it is surprising that there has been relatively little academic focus on the energy policies of the states. This paper attempts to partially fill the policy analysis 'gap' by investigating the present environmental aspects of the energy policies of NSW and Victoria, implemented since the signing of the UNFCCC in 1992. NSW and Victoria are Australia's most populous states and are responsible for the bulk of the nation's greenhouse gas emissions with two very distinct policies.  相似文献   

A Landscape Ecology Approach to Assessing Development Impacts in the Tropics: A Geothermal Energy Example in Hawaii   总被引：1，自引：0，他引：1  

Jerry A. Griffith  Carl C. Trettin  & Robert V. O'Neill 《Singapore journal of tropical geography》2002,23(1):1-22

Geographic information systems (GIS) are increasingly being used in environmental impact assessments (EIA) because GIS is useful for analysing spatial impacts of various development scenarios. Spatially representing these impacts provides another tool for landscape ecology in environmental and geographical investigations by facilitating analysis of the effects of landscape pattern on ecological processes and examining change over time. Landscape ecological principles are applied in this study to a hypothetical geothermal development project on the Island of Hawaii. Some common landscape pattern metrics were used to analyse dispersed versus condensed development scenarios and their effect on landscape pattern. Indices of fragmentation and patch shape did not appreciably change with additional development. The amount of forest to open edge, however, greatly increased with the dispersed development scenario. In addition, landscape metrics showed that a human disturbance had a greater simplifying effect on patch shape and also increased fragmentation than a natural disturbance. The use of these landscape pattern metrics can advance the methodology of applying GIS to EIA.  相似文献   

Medical geography as a science of interdisciplinary knowledge synthesis under conditions of uncertainty     

Daniel A. Griffith  George Christakos 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(5):459-460

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Constraining initial Th activity in incrementally deposited, biogenic aragonite from the Bahamas     

Brad E. Rosenheim  Peter K. Swart 《Geochimica et cosmochimica acta》2007,71(16):4025-4035

The ²³⁰Th content of subsurface Bahamas seawater has been estimated from incrementally deposited aragonite skeletons of sclerosponges using U-series age models which imply syndepositional incorporation of ²³⁰Th. First order age models, assuming constant growth rate and zero initial ²³⁰Th activity, display an average surface age of 63 ± 18 y despite the fact that the surfaces of the organisms were known to be alive at the time collection in the 1990s. A knowledge of the initial ²³⁰Th activity is necessary to incorporate the surface age constraint into an age model. In the Bahamas, this approach estimates an initial ²³⁰Th/²³²Th activity ratio of 4.3 ± 1.1 when applied to several individuals of the Caribbean sclerosponge Ceratoporella nicholsoni. These results differ from the same approach applied to previous work on Jamaican sclerosponges accreting aragonite in an environment closer to crustal sources and with less carbonate substrate. We report new measurements of Jamaican sclerosponge suggesting initial activity ratios of ²³⁰Th/²³²Th of ∼1, albeit with a high amount of uncertainty, indicating a regional difference in initial thorium activities. The estimates of initial ²³⁰Th/²³²Th activity ratios in the Bahamas are similar to the dissolved ratio rather than the particulate ratio and can be explained by mixing of open ocean water and bank-top surface water, however no information regarding temporal changes in the amount of initial ²³⁰Th/²³²Th activity available for incorporation into biogenic aragonite can be constrained using this approach. Growth rates do not change after correction for initial thorium and they display an inverse relationship with depth. Although this paper deals uniquely with sclerosponge aragonite, it is likely that the approach can be used on any incrementally deposited biogenic aragonite, provided information is known a priori about the first order growth model and there is evidence that initial thorium incorporation is representative of ambient environment rather than individual physiology.  相似文献