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  • 21
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    Which cropland greenhouse gas mitigation options give the greatest benefits in different world regions? Climate and soil specific predictions from integrated empirical models. (2012)
    Wiley
    Details
    Publication Date: 2012-02-22
    Description: Major sources of greenhouse gas (GHG) emissions from agricultural crop production are nitrous oxide (N 2 O) emissions resulting from the application of mineral and organic fertiliser, and carbon dioxide (CO 2 ) emissions from soil carbon losses. Consequently, choice of fertiliser type, optimising fertiliser application rates and timing, reducing microbial denitrification and improving soil carbon management are focus areas for mitigation. We have integrated separate models derived from global data on fertiliser induced soil N 2 O emissions, soil nitrification inhibitors, and the effects of tillage and soil inputs of soil C stocks into a single model in order to determine optimal mitigation options as a function of soil type, climate, and fertilisation rates. After Monte Carlo sampling of input variables we aggregated the outputs according to climate, soil and fertiliser factors to consider the benefits of several possible emissions mitigation strategies, and identified the most beneficial option for each factor class on a per hectare basis. The optimal mitigation for each soil-climate-region was then mapped to propose geographically specific optimal GHG mitigation strategies for crops with varying N requirements. The use of empirical models reduces the requirements for validation (since they are calibrated on globally or continentally observed phenomena). However, since they are relatively simple in structure, they may not be applicable for accurate site specific prediction of GHG emissions. The value of this modelling approach is for initial screening and ranking of potential agricultural mitigation options and to explore the potential impact of regional agricultural GHG abatement policies. Given the clear association between management practice and crop productivity, it is essential to incorporate characterisation of the yield effect on a given crop before recommending any mitigation practice.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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  • 22
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    Large-scale circulation features in the tropical western Pacific and their representation in climate models (2012)
    Wiley
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    Publication Date: 2012-02-25
    Description: Within the Western Pacific Monsoon (WPM) region the zonal component of the low-level winds tends to weaken and reverse from east to west during the peak monsoon season, which also marks a peak in rainfall. This study examines how well climate models can simulate these phenomena prior to evaluating their projections for later this century. While a seasonal wind reversal or weakening appears to be reasonably well simulated by most models over much of the WPM, the relationships between large-scale average winds and rainfall are not always well simulated. This allows us to discriminate among the models in order to see if this affects the projections. However, it so happens that this has relatively little effect, and the predominant signal is for an increase in rainfall with a weakening or negligible change to the low-level monsoon winds. These results indicate that the WPM climate will respond more to global scale drivers such as an increase in atmospheric water vapor content and a weakening of the global circulation, rather than to more regional changes such as an increase in the land/ocean temperature contrast.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 23
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    Lunar radiation environment and space weathering from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) (2012)
    Wiley
    Details
    Publication Date: 2012-03-13
    Description: The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) measures linear energy transfer by Galactic Cosmic Rays (GCRs) and Solar Energetic Particles (SEPs) on the Lunar Reconnaissance Orbiter (LRO) Mission in a circular, polar lunar orbit. GCR fluxes remain at the highest levels ever observed during the space age. One of the largest SEP events observed by CRaTER during the LRO mission occurred on June 7, 2011. We compare model predictions by the Earth-Moon-Mars Radiation Environment Module (EMMREM) for both dose rates from GCRs and SEPs during this event with results from CRaTER. We find agreement between these models and the CRaTER dose rates, which together demonstrate the accuracy of EMMREM, and its suitability for a real-time space weather system. We utilize CRaTER to test forecasts made by the Relativistic Electron Alert System for Exploration (REleASE), which successfully predicts the June 7th event. At the maximum CRaTER-observed GCR dose rate (∼11.7 cGy/yr where Gy is a unit indicating energy deposition per unit mass, 1 Gy = 1 J/kg), GCRs deposit ∼88 eV/molecule in water over 4 billion years, causing significant change in molecular composition and physical structure (e.g., density, color, crystallinity) of water ice, loss of molecular hydrogen, and production of more complex molecules linking carbon and other elements in the irradiated ice. This shows that space weathering by GCRs may be extremely important for chemical evolution of ice on the Moon. Thus, we show comprehensive observations from the CRaTER instrument on the Lunar Reconnaissance Orbiter that characterizes the radiation environment and space weathering on the Moon.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 24
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    On the temporal clustering of US floods and its relationship to climate teleconnection patterns (2012)
    Wiley
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    Publication Date: 2012-03-16
    Description: This article examines whether the temporal clustering of flood events can be explained in terms of climate variability or time-varying land-surface state variables. The point process modelling framework for flood occurrence is based on Cox processes, which can be represented as Poisson processes with randomly varying rate of occurrence. In the special case that the rate of occurrence is deterministic, the Cox process simplifies to a Poisson process. Poisson processes represent flood occurrences which are not clustered. The Cox regression model is used to examine the dependence of the rate of occurrence on covariate processes. We focus on 41 stream gauge stations in Iowa, with discharge records covering the period 1950–2009. The climate covariates used in this study are the North Atlantic Oscillation (NAO) and the Pacific/North American Teleconnection (PNA). To examine the influence of land-surface forcing on flood occurrence, the antecedent 30 d rainfall accumulation is considered. In 27 out of 41 stations, either PNA or NAO, or both are selected as significant predictors, suggesting that flood occurrence in Iowa is influenced by large-scale climate indices. Antecedent rainfall, used as a proxy for soil moisture, plays an important role in driving the occurrence of flooding in Iowa. These results point to clustering as an important element of the flood occurrence process. Copyright © 2012 Royal Meteorological Society
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
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  • 25
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    An annual cycle of size-resolved aerosol hygroscopicity at a forested site in Colorado (2012)
    Wiley
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    Publication Date: 2012-03-16
    Description: The ability of particles composed wholly or partially of biogenic secondary organic compounds to serve as cloud condensation nuclei (CCN) is a key characteristic that helps to define their roles in linking biogeochemical and water cycles. In this paper, we describe size-resolved (14–350 nm) CCN measurements from the Manitou Experimental Forest in Colorado, where particle compositions were expected to have a large biogenic component. These measurements were conducted for 1 year as part of the Bio-hydro-atmosphere Interactions of Energy, Aerosols, Carbon, H2O, Organics, and Nitrogen program and determined the aerosol hygroscopicity parameter, κ, at five water supersaturations between ∼0.14% and ∼0.97%. The average κ value over the entire study and all supersaturations was κavg = 0.16 ± 0.08. Kappa values decreased slightly with increasing supersaturation, suggesting a change in aerosol composition with dry diameter. Furthermore, some seasonal variability was observed with increased CCN concentrations and activated particle number fraction, but slightly decreased hygroscopicity, during the summer. Small particle events, which may indicate new particle formation, were observed throughout the study period, especially in the summer, leading to increases in CCN concentration, followed by a gradual increase in the aerosol mode size. The condensing material appeared to be predominantly composed of organic compounds and led to a small decrease in κ at the larger activation diameters during and immediately after those events.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 26
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    On virtual observatories and modelled realities (or why discharge must be treated as a virtual variable) (2012)
    Wiley
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    Publication Date: 2012-02-14
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 27
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    Controls on floc growth in an energetic tidal channel (2012)
    Wiley
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    Publication Date: 2012-02-14
    Description: Measurements of turbulence and suspended particle characteristics have been made continuously for 9 tidal cycles in a shallow, energetic tidal channel. Particle-size spectra were measured with a LISST-100 laser diffraction instrument placed on a frame on the seabed. A 1200 kHz ADCP in the same frame was used to measure vertical current profiles and from these the turbulent kinetic energy dissipation rate was determined using the structure function method. Median particle size is observed to change in a regular way by a factor of 3 or more over each tidal cycle, with the largest particles observed at slack tide and the smallest at times of maximum flood and ebb. The most likely explanation of this change is that particles are aggregating at times of low turbulence and breaking up during fast flows. A simple dynamical flocculation model that incorporates these processes gives good agreement with observations, particularly if tidal advection of a longitudinal gradient in particle size is allowed for. If particles have time to reach equilibrium with ambient conditions, the model predicts that the particle size will be proportional to the product of concentration and the Kolmogorov microscale. The observations support this prediction on most tidal cycles if a phase lag (of 30–60 min) is allowed between the measurements of particle size and Kolmogorov scale. This phase lag represents the adjustment time for flocs to respond to change in turbulence. The constant of proportionality between median particle size and Kolmogorov scale increases with particle volume.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 28
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    Influence of permafrost on water storage in West Siberian peatlands revealed from a new database of soil properties (2012)
    Wiley
    Details
    Publication Date: 2012-02-16
    Description: ABSTRACT Russia's West Siberian Lowland (WSL) contains the most extensive peatlands on Earth with many underlain by permafrost. We present a new database of 12 705 measurements of vertical water content and bulk soil properties from 98 permafrost and non-permafrost cores collected in raised bogs and peat plateaus across the region, together with in-situ measurements of surface moisture and thaw depth, botanical descriptions of dominant surface vegetation species assemblage, and field notes. Data analyses reveal significant contrasts ( p  〈 0.01 to p  〈 0.0001) between permafrost and non-permafrost sites. On average, permafrost WSL peatlands exhibit drier surfaces, shallower depth, lower organic matter content and higher bulk density than do non-permafrost sites. Peat bulk density and ash-free density increase with depth for non-permafrost but not for permafrost sites. Gravimetric water content averages 92.0% near the surface and 89.3% at depth in non-permafrost, but 81.6% and 85.4%, respectively, in permafrost, suggesting that the disappearance of permafrost could produce moister surfaces across the WSL. GIS extrapolation of these results suggests that WSL peatlands may contain ~1200 km 3 of water and ice, a large storage equivalent to ~2-m average liquid water depth and approximately three times the total annual flow in the Ob' River. A global estimate of ~6900-km 3 subsurface water storage for all northern peatlands suggests a volume comparable to or greater than the total water storage in northern lakes. The database is freely available as supplementary material for scientific use. Copyright © 2012 John Wiley & Sons, Ltd.
    Print ISSN: 1045-6740
    Electronic ISSN: 1099-1530
    Topics: Geography , Geosciences
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  • 29
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    Solid Solution Effects on the Thermal Properties in the MgAl2O4–MgGa2O4 System (2012)
    Wiley
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    Publication Date: 2012-12-25
    Description: Solid solution effects on thermal conductivity within the MgO – Al 2 O 3 – Ga 2 O 3 system were studied. Samples with systematically varied additions of MgGa 2 O 4 – MgAl 2 O 4 were prepared and the laser flash technique was used to determine thermal diffusivity at temperatures between 200°C and 1300°C. Heat capacity as a function of temperature from room temperature to 800°C was also determined using differential scanning calorimetry (DSC). Solid solution in the MgAl 2 O 4 – MgGa 2 O 4 system decreases the thermal conductivity up to 1000°C. At 200°C thermal conductivity decreased 24% with a 5 mol% addition of MgGa 2 O 4 to the system. At 1000°C, the thermal conductivity decreased 13% with a 5 mol% addition. Steady-state calculations showed a 12.5% decrease in heat flux with 5 mol% MgGa 2 O 4 considered across a 12 inch thickness.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 30
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    Temperature-induced marine export production during glacial period (2012)
    Wiley
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    Publication Date: 2012-11-08
    Description: Proxy records indicate that export production was enhanced at the onset of the last glaciation. We examine how glacial cooling affects marine export production through temperature-dependent phytoplankton productivity and organic carbon remineralization using glacial climate simulation. Compared with the standard assumption of no temperature dependence as applied in existing paleoclimate models, including temperature-dependence enhances export production globally under glacial climate conditions. The near freezing temperatures of Antarctic seawater significantly reduce organic carbon remineralization. Less remineralization than production results in increasing carbon export to the deep ocean. Nutrients remaining near the surface at high latitudes are advected to lower latitudes via Antarctic Intermediate Water, enhancing primary production, and hence export, in temperate and tropical regions as well. Including temperature-dependence improves the model's agreement with the glacial proxy records of export production and stable carbon isotopes even under stably stratified conditions with a weakening of North Atlantic Deep Water.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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