Hemispheric-scale climate response to Northern Eurasia land surface characteristics and snow anomalies   总被引：3，自引：0，他引：3  

Gavin Gong  Judah Cohen  Dara Entekhabi  Yan Ge   《Global and Planetary Change》2007,56(3-4):359

This paper presents a synopsis of recently published studies by the co-authors, which show that several land surface characteristics unique to Northern Eurasia are responsible for facilitating a causal relationship between autumn snow anomalies in this region and subsequent hemispheric winter climate patterns. The large size and extratropical location of the contiguous Eurasian land mass results in broad, continental-scale interannual snow cover extent and depth variations throughout autumn and winter, and corresponding diabatic heating anomalies. These surface anomalies occur in the presence of a large region of stationary wave activity, produced in part by the orographic barriers that separate northern/central Eurasia from southern/eastern Eurasia. This co-location of snow-forced anomalies and ambient wave energy is unique to Northern Eurasia, and initiates a teleconnection pathway involving stationary wave–mean flow interaction throughout the troposphere and stratosphere, ultimately resulting in a modulation of the winter Arctic Oscillation (AO). Complementary new results are also presented which show that partial snow cover extent or snow depth only anomalies in Northern Eurasia are insufficient to initiate the teleconnection pathway and produce a winter AO signal. This synopsis provides a useful interpretation of the earlier studies in the specific context of Northern Eurasia regional climate and environmental change.  相似文献   

Investigations of the bottom current sculpted margin of Hatton Bank, NE Atlantic     

Suzanne E. MacLachlan  Gavin M. Elliott  Lindsay M. Parson 《Marine Geology》2008,253(3-4):170-184

The northwest Hatton Bank margin is an ideal locality to demonstrate the interaction between bottom currents and slope configuration in controlling the distribution and morphology of bottom current deposits. The slope area investigated is isolated from any major terrigenous sediment supply and at present is influenced by the Deep Northern Boundary Current (DNBC). Swath bathymetry and high resolution acoustic data allow us to evaluate both local and regional controls on slope sedimentation and the possible mechanisms for bottom-current velocity variability across a slope setting within the NW European continental margin. The slope exhibits sculpting by bottom currents that flow in a predominantly southwest to northeast direction, and is only locally modified by slope failures. Positive relief features such as the Endymion Spur play an important role in constraining and accelerating bottom-current flow and, consequently, in redistributing sediment along the margin. We demonstrate that the size, morphology and distribution of bottom-current deposits along the slope vary as a function of the interaction between bottom currents, regional slope orientation and local seafloor topography.  相似文献   

The linkage between fault throw and footwall scarp erosion patterns: an example from the Bremstein Fault Complex,offshore Mid‐Norway     

Gavin M. Elliott  Paul Wilson  Christopher A.‐L. Jackson  Robert L. Gawthorpe  Lisa Michelsen  Ian R. Sharp 《Basin Research》2012,24(2):180-197

Studies of normal fault systems in modern extensional regimes (e.g. Basin and Range), and in exhumed, ancient rift basins (e.g. Gulf of Suez Rift) have shown a link between the evolution of fault‐related footwall topography and associated erosional drainage systems. In this study, we use 3D seismic reflection data to image the footwall crest of a gravity‐driven fault system developed during late Middle Jurassic to Early Cretaceous rifting on the Halten Terrace, offshore Mid‐Norway. This 22‐km‐long fault system lacks significant footwall uplift, with hangingwall subsidence accommodating throw accumulation on the fault system. Significant erosion has occurred along the length of the footwall crest and is defined by 96 catchments characterized by erosional channels. These erosional channels consist of small, linear systems up to 750 m long located along the front of the fault footwall. Larger, dendritic channel systems extend further back (up to 3 km normal to fault strike) into the footwall. These channels are up to 7 km long, up to 50 m deep and up to 1 km wide. Fault throw varies along strike, with greatest throw in the centre of the fault decreasing towards the fault tips; localized throw minima are interpreted to represent segment linkage points, which were breached as the fault grew. Comparison of the catchment location to the throw distribution shows that the largest catchments are in the centre of the fault and decrease in size to the fault tips. There is no link between the location of the breached segment linkage points and the location and size of the footwall catchments, suggesting that the first‐order control on footwall erosion patterns is the overall fault‐throw distribution.  相似文献   

2XMMi J225036.9+573154 – a new eclipsing AM Her binary discovered using XMM–Newton     

Gavin Ramsay  Simon Rosen  Pasi Hakala  Thomas Barclay 《Monthly notices of the Royal Astronomical Society》2009,395(1):416-421

We report the discovery of an eclipsing polar, 2XMMi J225036.9+573154, using XMM–Newton . It was discovered by searching the light curves in the 2XMMi catalogue for objects showing X-ray variability. Its X-ray light curve shows a total eclipse of the white dwarf by the secondary star every 174 min. An extended pre-eclipse absorption dip is observed in soft X-rays at  φ= 0.8–0.9  , with evidence for a further dip in the soft X-ray light curve at  φ∼ 0.4  . Further, X-rays are seen from all orbital phases (apart from the eclipse) which make it unusual amongst eclipsing polars. We have identified the optical counterpart, which is faint  ( r = 21)  , and shows a deep eclipse (>3.5 mag in white light). Its X-ray spectrum does not show a distinct soft X-ray component which is seen in many, but not all, polars. Its optical spectrum shows Hα in emission for a fraction of the orbital period.  相似文献   

Microgeographies of Retailing and Gentrification   总被引：2，自引：0，他引：2  

Gary Bridge  Robyn Dowling 《The Australian geographer》2001,32(1):93-107

It has long been argued that gentrification is a process of consumption as well as production but, in the main, analyses of consumption and gentrification have only tangentially or anecdotally considered the retail spaces of gentrified neighbourhoods. In this paper we investigate the nature of the retail landscapes of gentrification, using empirical evidence from Sydney, Australia. We point to micro retailscapes that differ between gentrified neighbourhoods that suggest a divergence of consumption practices between different groups of gentrifiers. These consumption practices are considered both in terms of their relations to identity (through food and the conception of the body) and to the spaces of the city. The paper concludes by drawing out the implications for future research on the consumption practices of the new middle class and the working class in an international context .  相似文献   

Temporal variation in discharge chemistry and portal flow from the 8-Level adit, Lynx Mine, Myra Falls Operations, Vancouver Island, British Columbia     

Alexandre J. Desbarats  Gavin C. Dirom 《Environmental Geology》2005,47(3):445-456

The Lynx mine, currently inactive, has produced copper and zinc concentrates from massive sulfide deposits on a lease within the rainy, mountainous interior of Vancouver Island. Tailings, used to back-fill a mined-out stope, are being leached by percolating groundwater and the resulting acidic, metal-laden drainage is discharging from the portal of the 8-Level adit. Temporal variations in the flow rate, specific conductance and temperature of the discharge were monitored continuously over a 2-year period while effluent chemistry was sampled weekly. Conductivity was relatively constant throughout most of the year but peaked with the first autumn storm events as accumulated soluble sulfide oxidation products were flushed from the workings. Concentrations of sulfate and most metals were closely correlated with conductivity as were low pH values as stored acidity was released along with dissolved species. Variations in pH controlled the speciation and partitioning of metals between dissolved and particulate phases.  相似文献   

Physical Geography: A Human Perspective by Richard Huggett, Sarah Lindley, Helen Gavin and Kate Richardson     

Gavin K Gillmore  David Cotton  William Hale 《Area》2006,38(2):226-226

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White dwarf masses in magnetic cataclysmic variables: multi-temperature fits to Ginga data     

Mark Cropper  Gavin Ramsay  & Kinwah Wu 《Monthly notices of the Royal Astronomical Society》1998,293(3):222-232

One method of obtaining the mass of the white dwarf in magnetic cataclysmic variables (mCVs) is through their hard X-ray spectra. However, previous mass estimates using this method give lower limits because the temperature of the plasma in the post-shock region (where the hard X-rays are emitted) is lower than the temperature of the shock itself. In AM Her systems, the additional cooling of the post-shock plasma by cyclotron emission will further lower the derived mass. Here we present estimates of the masses of the white dwarf in 13 mCVs derived using Ginga data and a model in which X-rays are emitted from a multi-temperature emission region with the appropriate temperature and density profile. We include in the model reflection from the surface of the white dwarf and a partially ionized absorber. We are able to achieve good fits to the data. We compare the derived masses with previous estimates and the masses for larger samples of isolated white dwarfs and those in CVs.  相似文献   

The power spectrum of rich clusters of galaxies on large spatial scales     

Helen Tadros  George Efstathiou  & Gavin Dalton 《Monthly notices of the Royal Astronomical Society》1998,296(4):995-1003

We present an analysis of the redshift-space power spectrum, P ( k ), of rich clusters of galaxies based on an automated cluster catalogue selected from the APM Galaxy Survey. We find that P ( k ) can be approximated by a power law, P ( k )∝ kⁿ , with n ≈−1.6 over the wavenumber range 0.04< k <0.1 h Mpc⁻¹. Over this range of wavenumbers, the APM cluster power spectrum has the same shape as the power spectra measured for optical and IRAS galaxies. This is consistent with a simple linear bias model in which different tracers have the same power spectrum as that of the mass distribution, but shifted in amplitude by a constant biasing factor. On larger scales, the power spectrum of APM clusters flattens and appears to turn over on a scale k ∼0.03 h Mpc⁻¹. We compare the power spectra estimated from simulated APM cluster catalogues with those estimated directly from cubical N -body simulation volumes, and find that the APM cluster survey should give reliable estimates of the true power spectrum at wavenumbers k ≳0.02 h Mpc⁻¹. These results suggest that the observed turnover in the power spectrum may be a real feature of the cluster distribution, and that we have detected the transition to a near-scale-invariant power spectrum implied by observations of anisotropies in the cosmic microwave background radiation. The scale of the turnover in the cluster power spectrum is in good agreement with the scale of the turnover observed in the power spectrum of APM galaxies.  相似文献   

Late Quaternary shedding of shallow-marine carbonate along a tropical mixed siliciclastic–carbonate shelf: Great Barrier Reef, Australia     

Gavin B. Dunbar†  Gerald R. Dickens†‡ 《Sedimentology》2003,50(6):1061-1077

Abstract The north-east Australian margin is the largest modern example of a tropical mixed siliciclastic/carbonate depositional system, with an outer shelf hosting the Great Barrier Reef (GBR) and an inner shelf dominated by fluvially sourced siliciclastic sediment wedges. The long-term interplay between these sediment components and sea level is recorded in the Queensland Trough, a 1–2 km deep N–S elongate basin situated between the GBR platform and the Queensland Plateau. In this paper, 154 samples from 45 surface grabs and six well-dated piston cores were analysed for total carbonate content, carbonate mineralogy and Sr concentration to establish spatial and temporal patterns of carbonate accumulation in the Queensland Trough over the last 300 kyr. Surface carbonate contents are lowest on the inner-shelf (<5%) and in the trough axis (<60%) because of siliciclastic dilution. Carbonate on the shelf is mostly Sr-rich aragonite and high-Mg calcite (HMC), whereas that in the basin is mostly low-Mg calcite. Once normalized to remove the effects of siliciclastic dilution, surface Sr-rich aragonite and HMC abundances decrease linearly to background levels ≈ 100 km seaward of the shelf edge. Core samples show that, over time, normalized aragonite and Sr abundances are greatest during periods of shelf flooding and lowest when sea level drops below the shelf edge. This is consistent with changes in the production of coral and calcareous algae, and the shedding of their debris from the shelf. Interestingly, normalized HMC concentrations on the slope peak during periods of major transgression, perhaps because of maximum off-shelf transport from inter-reef areas or intermediate water dissolution. After accounting for siliciclastic dilution, there are strong similarities in both spatial and temporal patterns of carbonate minerals between slopes and basins of the north-east Australian margin and those of pure carbonate margins such as the Bahamas. A limited set of basic processes, including the formation and breakdown of carbonate on the shelf, the transport of carbonate off the shelf and eustatic sea level, probably controls carbonate accumulation in slope and basin settings of tropical environments, irrespective of proximal siliciclastic sediment sources.  相似文献