THE METEOR FLUX: IT DEPENDS HOW YOU LOOK     

Lars P. Dyrud  Kelly Denney  Julio Urbina  Diego Janches  Erhan Kudeki  Steve Franke 《Earth, Moon, and Planets》2004,95(1-4):89-100

In this paper, we use radar observations from a 50 MHz radar stationed near Salinas, Puerto Rico, to study the variability of specular as well as non-specular meteor trails in the E-region ionosphere. The observations were made from 18:00 to 08:00 h AST over various days in 1998 and 1999 during the Coqui II Campaign [Urbina et al., 2000, Geophys. Rev. Lett. 27, 2853–2856]. The radar system had two sub-arrays, both produced beams pointed to the north in the magnetic meridian plane, perpendicular to the magnetic field, at an elevation angle of approximately 41 degrees. The Coqui II radar is sensitive to at least two types of echoes from meteor trails: (1) Specular reflections from trails oriented perpendicular to the radar beam, and (2) scattering, or, non-specular reflections, from trails deposited with arbitrary orientations. We examine and compare the diurnal and seasonal variability of echoes from specular and non-specular returns observed with the Coqui II radar. We also compare these results with meteor head echo observations made with the Arecibo 430 MHz radar. We use common region observations of these three types of meteor echoes to show that the diurnal and seasonal variability of specular trails, non-specular trails, and head echoes are not equivalent. The implications of these results on global meteor mass flux estimates obtained from specular meteor observations remains to be examined.  相似文献   

Geotechnical and mineralogical characteristics of marl deposits in Jordan   总被引：1，自引：0，他引：1  

Fathi M. Shaqour  Ghaleb Jarrar  Steve Hencher  Mostafa Kuisi 《Environmental Geology》2008,55(8):1777-1783

Marls and marly limestone deposits cover most of Northern Jordan, where Amman City and its suburbs are located. These deposits serve as foundations for most buildings and roads as well as fill material for structural back filling, especially road bases and sub-bases. The present study aims at investigating the geotechnical characteristics and mineral composition of the marl units of these deposits through field investigations and laboratory testing. Using X-ray diffraction technique along with chemical analysis, representative samples of marl horizons were tested for mineral composition, and for a set of index and geotechnical properties including: specific gravity, grain size, Atterberg limits, Proctor compaction and shear strength properties. The test results show a positive linear relationship as expected between the clay content and both liquid and plastic limits. The tests results also show an inverse linear relationship between the clay content and the maximum dry density in both standard and modified compaction. This is attributed to the adsorption of water by the clay minerals. The relationship is more prominent in the case of modified compaction test. The results also indicate a similar relationship for the angle of internal friction. No clear correlation between cohesion and clay content was apparent.  相似文献   

Sensitivity of the global atmospheric cycle of mercury to emissions     

Kristen Lohman  Christian Seigneur  Mae Gustin  Steve Lindberg 《Applied Geochemistry》2008

A systematic investigation of the impact of current uncertainties in Hg emissions from specific source categories on global air Hg concentrations is presented. First, the uncertainties in different emission source categories are discussed and then the results of a base simulation and three sensitivity simulations conducted with a global chemical transport model for mercury (CTM-Hg) are presented. The total Hg emissions in the four scenarios range from 6600 to 9400 Mg/a. The sensitivity studies investigate the impact of the range in uncertainty in natural emissions, emissions of previously deposited Hg, and anthropogenic emissions both in China and worldwide, while taking into account constraints imposed by available data (current/pre-industrial emission ratio of 2–4). In one case, natural emissions and emissions of previously deposited Hg were changed to represent a mid point of the range of values found in the literature. This lead to a 16% increase in background emissions, i.e., natural emissions and emissions of previously deposited Hg combined. Increasing natural emissions by 16% or Chinese anthropogenic emissions by 100% yielded atmospheric Hg concentrations comparable with those measured across the globe without any changes to the atmospheric chemistry. Increasing natural emissions and emissions of previously deposited Hg by 16% and all anthropogenic emissions by 100% as compared to the base scenario yielded atmospheric Hg concentrations that were not compatible with measurements and changes in the chemical behavior of Hg in the atmosphere would be required to yield results that are consistent with observed Hg concentrations. The current uncertainty in total Hg emissions at the global scale is placed at about a factor of two.  相似文献   

Distribution and significance of long-chain alkenones as salinity and temperature indicators in Spanish saline lake sediments     

Emma J. Pearson  Steve Juggins 《Geochimica et cosmochimica acta》2008,72(16):4035-4046

We investigated relationships between sedimentary solvent-extractable long-chain alkenone (LCA) concentration and composition and environmental factors in a suite of endorheic lakes from inland Spain. LCAs were found in 14 of the 54 lakes examined, with concentrations comparable with those from previously published lacustrine settings. The composition of LCAs in our sites, however, contrast from the majority of those previously reported from lake environments; in our study the tri-unsaturated component is the most abundant component at most sites where LCAs are detected, and C_38:3 is the most abundant LCA in the majority of sites. LCA occurrence appears to be restricted to brackish-hypersaline sites and C₃₇ LCAs are absent above a salinity of ∼40 g L⁻¹ suggesting a salinity control on LCA-producing organisms in these sites. Low concentrations of C₃₇ LCA components means and temperature indices are generally not applicable. Instead we find good relationships between C₃₈ components and (in particular mean autumn) temperature and the strongest LCA-temperature relationships are found when using a combination of all C₃₇ and C₃₈ compounds. We propose a new alkenone temperature index for lakes with elevated salinity and where the C₃₈ components dominate the LCA distributions. This is expressed as (r² = 0.80, n = 13). In this paper, we provide the first account of sedimentary LCA distributions from lakes in inland Spain, extending the range of environments within which these compounds have been found and highlighting their significance as indicators of both salinity and temperature in saline, endorheic lake environments. This has important implications for extending the potential role of LCAs as palaeoclimatic indicators in lacustrine environments.  相似文献   

Reconstituting nature conservation: Towards a careful political ecology   总被引：1，自引：0，他引：1  

Steve Hinchliffe 《Geoforum》2008,39(1):88-97

This paper is about the relationship between nature conservation in theory and nature conservation in practice. I argue that in theory nature conservation is concerned with revealing presence and rendering the present eternal. In practice, the spaces and times of conservation are less clear. Conservationists work with matters of concern that are neither self-evident nor unproblematically co-present. Presence has to be made and re-made. These matters of concern, like rare species, do not always announce themselves to political ecology and they do not always perform to type. Such difficulties are analysed through discussion of practical work conducted in a UK city with field ecologists and nonhuman inhabitants. It is argued that a careful political ecology is one that is intent on making spaces for others that are not simply about presence, inclusion or accumulation. It also involves uncertainties, precautionary measures and looser forms of assemblage.  相似文献   

A Tribute to Rick and Debbie Jahnke: From Deep Sea Pore Water to Coastal Permeable Sediments-Contributions that Cover the Oceans     

Timothy J. Shaw  Steve Emerson  Herbert L. Windom 《Aquatic Geochemistry》2016,22(5-6):391-399

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The 10th Antarctic meteorological observation,modeling, and forecasting workshop     

Steve R. Colwell  Arthur M. Cayette  Matthew A. Lazzara  Jordan G. Powers  David H. Bromwich  John J. Cassano  Scott Carpentier 《大气科学进展》2016,33(5):656-658

正1.Overview The 10th Antarctic Meteorological Observation,Modeling,and Forecasting Workshop(hereinafter AMOMFW)took place June 17–19,2015 in the historic city of Cambridge,United Kingdom.The meeting followed its purpose of connecting Antarctic atmospheric science to weatherrelated operational issues and advances in observing,modeling,forecasting,and understanding the Antarctic environ-  相似文献   

Abrupt summer warming and changes in temperature extremes over Northeast Asia since the mid-1990s: Drivers and physical processes     

Buwen Dong  Rowan T. Sutton  Wei Chen  Xiaodong Liu  Riyu Lu  Ying Sun 《大气科学进展》2016,33(9):1005-1023

This study investigated the drivers and physical processes for the abrupt decadal summer surface warming and increases in hot temperature extremes that occurred over Northeast Asia in the mid-1990 s. Observations indicate an abrupt increase in summer mean surface air temperature(SAT) over Northeast Asia since the mid-1990 s. Accompanying this abrupt surface warming, significant changes in some temperature extremes, characterized by increases in summer mean daily maximum temperature(Tmax), daily minimum temperature(Tmin), annual hottest day temperature(TXx), and annual warmest night temperature(TNx) were observed. There were also increases in the frequency of summer days(SU) and tropical nights(TR).Atmospheric general circulation model experiments forced by changes in sea surface temperature(SST)/ sea ice extent(SIE),anthropogenic greenhouse gas(GHG) concentrations, and anthropogenic aerosol(AA) forcing, relative to the period 1964–93, reproduced the general patterns of observed summer mean SAT changes and associated changes in temperature extremes,although the abrupt decrease in precipitation since the mid-1990 s was not simulated. Additional model experiments with different forcings indicated that changes in SST/SIE explained 76% of the area-averaged summer mean surface warming signal over Northeast Asia, while the direct impact of changes in GHG and AA explained the remaining 24% of the surface warming signal. Analysis of physical processes indicated that the direct impact of the changes in AA(through aerosol–radiation and aerosol–cloud interactions), mainly related to the reduction of AA precursor emissions over Europe, played a dominant role in the increase in TXx and a similarly important role as SST/SIE changes in the increase in the frequency of SU over Northeast Asia via AA-induced coupled atmosphere–land surface and cloud feedbacks, rather than through a direct impact of AA changes on cloud condensation nuclei. The modelling results also imply that the abrupt summer surface warming and increases in hot temperature extremes over Northeast Asia since the mid-1990 s will probably sustain in the next few decades as GHG concentrations continue to increase and AA precursor emissions over both North America and Europe continue to decrease.  相似文献   

Preferred response of the East Asian summer monsoon to local and non-local anthropogenic sulphur dioxide emissions     

Buwen Dong  Rowan T. Sutton  Eleanor J. Highwood  Laura J. Wilcox 《Climate Dynamics》2016,46(5-6):1733-1751

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Exploring national decarbonization pathways and global energy trade flows: a multi-scale analysis     

Steve Pye  Christophe McGlade  Chris Bataille  Gabrial Anandarajah  Amandine Denis-Ryan  Vladimir Potashnikov 《Climate Policy》2016,16(4):S92-S109

The role of fossils fuels in national economies will change radically over the next 40 years under a strong climate regime. However, capturing this changing role through national-based analyses is challenging due to the global nature of fossil fuel demand and resulting trade patterns. This article sets out the limitations of existing national-scale decarbonization analyses in adequately capturing global conditions and explores how the introduction of a global modelling framework could provide vital insights, particularly for those countries that are dependent on fossil fuel exports or imports.

The article shows that fossil fuel use will significantly decline by 2050, although gas will have an important transition role. This leaves large fossil fuel exporters exposed, the extent of which is determined by mitigation action in different regions and especially by the pathways adopted by the larger Asian economies. We find that global-scale models provide critical insights that complement the more detailed national analyses and should play a stronger role in informing deep decarbonization pathways (DDPs). They also provide an important basis for exploring key uncertainties around technology uptake, mitigation rates and how this plays out in the demand for fossil fuels. However, use of global models also calls for improved representation of country specifics in global models, which can oversimplify national economic and political realities. Using both model scales provides important insights that are complementary but that can challenge the other’s orthodoxy. However, neither can replace the other’s strengths.

Policy relevance:

In recent years, how global fossil fuel markets will evolve under different climate regimes has been subject to much debate and analysis. This debate includes whether investments in fossil fuel production still make sense or will be exposed in the future to liabilities associated with high carbon prices. This is important for governments who need to develop coherent policy in relation to fossil fuel sectors and their role as drivers of economic growth and in providing for domestic energy needs. This article argues that national analyses need to be fully cognizant of the global-scale transition, which can be informed by using a multi-scale modelling approach.  相似文献