Measurements of Flows Over Isolated Valleys     

Brian?Garvey  Ian?P.?CastroEmail author  Giles?Wiggs  Joanna?Bullard 《Boundary-Layer Meteorology》2005,117(3):417-446

Wind-tunnel measurements of the flow over an isolated valley both normal and at an angle (45°) to a simulated neutrally stable atmospheric boundary layer are presented. Attention is concentrated on the nature of the flow within the valley itself. The work formed part of a wider study that included detailed field measurements around an African desert valley and some limited comparisons with that work are included. A scale of about 1:1000 was used for the laboratory work, in which an appropriate combination of hot wire and particle image velocimetry was employed. For a valley normal to the upwind flow, it is shown that the upstream influence of the valley extends to a distance of at least one half of the axial valley width upstream of the leading edge, whereas differences in mean flow and turbulence could be identified well beyond two valley widths from the downwind edge. Non-normal wind angles lead to significant along-valley flows within the valley and, even at two valley heights above the valley ridge level, there remains a significant spanwise flow component. Downwind turbulence levels are somewhat lower in this case, but are still considerably higher than in the undisturbed boundary layer. At both flow angles, there are significant recirculation regions within the valleys, starting from mean separation just beyond the leading edge, but the strong spanwise flow in the 45° case reduces the axial extent of the separated zone. The flow is shown to be in some ways analogous to flow over an isolated hill. Our results usefully enhance the field data and could be used to improve modelling of saltation processes in the field.  相似文献   

The Scale of VGI in Map Production: A Perspective on European National Mapping Agencies          下载免费PDF全文

Ana‐Maria Olteanu‐Raimond  Glen Hart  Giles M. Foody  Guillaume Touya  Tobias Kellenberger  Demetris Demetriou 《Transactions in GIS》2017,21(1):74-90

The perspective of European National Mapping Agencies (NMA) on the role of citizen sensing in map production was explored. The NMAs varied greatly in their engagement with the community generating volunteered geographic information (VGI) and in their future plans. From an assessment of NMA standard practices, it was evident that much VGI was acquired with a positional accuracy that, while less than that typically acquired by NMAs, actually exceeded the requirements of the nominal data capture scale used by most NMAs. Opportunities for VGI use in map revision and updating were evident, especially for agencies that use a continuous rather than cyclical updating policy. Some NMAs had also developed systems to engage with citizen sensors and examples are discussed. Only rarely was VGI used to collect data on features beyond the standard set used by the NMAs. The potential role of citizen sensing and so its current scale of use by NMAs is limited by a series of concerns, notably relating to issues of data quality, the nature and motivation of the contributors, legal issues, the sustainability of data source, and employment fears of NMA staff. Possible priorities for future research and development are identified to help ensure that the potential of VGI in mapping is realized.  相似文献   

Neutralizing homelessness, 2015: the story to date     

David Boarder Giles 《Urban geography》2017,38(3):332-340

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Solar modulation in surface atmospheric electricity     

R. Giles Harrison  Ilya Usoskin 《Journal of Atmospheric and Solar》2010,72(2-3):176-182

The solar wind modulates the flux of galactic cosmic rays impinging on Earth inversely with solar activity. Cosmic ray ionisation is the major source of air's electrical conductivity over the oceans and well above the continents. Differential solar modulation of the cosmic ray energy spectrum modifies the cosmic ray ionisation at different latitudes, varying the total atmospheric columnar conductance. This redistributes current flow in the global atmospheric electrical circuit, including the local vertical current density and the related surface potential gradient. Surface vertical current density and potential gradient measurements made independently at Lerwick Observatory, Shetland, from 1978 to 1985 are compared with modelled changes in cosmic ray ionisation arising from solar activity changes. Both the lower troposphere atmospheric electricity quantities are significantly increased at cosmic ray maximum (solar minimum), with a proportional change greater than that of the cosmic ray change.  相似文献   

Land cover classification by an artificial neural network with ancillary information     

Giles M. Foody 《International journal of geographical information science》2013,27(5):527-542

Abstract

Remote sensing is an important source of land cover data required by many GIS users. Land cover data are typically derived from remotely–sensed data through the application of a conventional statistical classification. Such classification techniques are not, however, always appropriate, particularly as they may make untenable assumptions about the data and their output is hard, comprising only the code of the most likely class of membership. Whilst some deviation from the assumptions may be tolerated and a fuzzy output may be derived, making more information on class membership properties available, alternative classification procedures are sometimes required. Artificial neural networks are an attractive alternative to the statistical classifiers and here one is used to derive a fuzzy classification output from a remotely–sensed data set that may be post–processed with ancillary data available in a GIS to increase the accuracy with which land cover may be mapped. With the aid ancillary information on soil type and prior knowledge of class occurrence the accuracy of an artificial neural network classification was increased by 29–93 to 77–37 per cent. An artificial neural network can therefore be used generate a fuzzy classification output that may be used with other data sets in a GIS, which may not have been available to the producer of the classification, to increase the accuracy with which land cover may be classified.  相似文献   

Energetic Charged Particles Above Thunderclouds     

Martin Füllekrug  Declan Diver  Jean-Louis Pinçon  Alan D. R. Phelps  Anne Bourdon  Christiane Helling  Elisabeth Blanc  Farideh Honary  R. Giles Harrison  Jean-André Sauvaud  Jean-Baptiste Renard  Mark Lester  Michael Rycroft  Mike Kosch  Richard B. Horne  Serge Soula  Stéphane Gaffet 《Surveys in Geophysics》2013,34(1):1-41

The French government has committed to launch the satellite TARANIS to study transient coupling processes between the Earth’s atmosphere and near-Earth space. The prime objective of TARANIS is to detect energetic charged particles and hard radiation emanating from thunderclouds. The British Nobel prize winner C.T.R. Wilson predicted lightning discharges from the top of thunderclouds into space almost a century ago. However, new experiments have only recently confirmed energetic discharge processes which transfer energy from the top of thunderclouds into the upper atmosphere and near-Earth space; they are now denoted as transient luminous events, terrestrial gamma-ray flashes and relativistic electron beams. This meeting report builds on the current state of scientific knowledge on the physics of plasmas in the laboratory and naturally occurring plasmas in the Earth’s atmosphere to propose areas of future research. The report specifically reflects presentations delivered by the members of a novel Franco-British collaboration during a meeting at the French Embassy in London held in November 2011. The scientific subjects of the report tackle ionization processes leading to electrical discharge processes, observations of transient luminous events, electromagnetic emissions, energetic charged particles and their impact on the Earth’s atmosphere. The importance of future research in this area for science and society, and towards spacecraft protection, is emphasized.  相似文献   

Crystal reaming during the assembly, maturation, and waning of an eleven-million-year crustal magma cycle: thermobarometry of the Aucanquilcha Volcanic Cluster   总被引：1，自引：1，他引：0  

Barry A. Walker Jr.  Erik W. Klemetti  Anita L. Grunder  John H. Dilles  Frank J. Tepley  Denise Giles 《Contributions to Mineralogy and Petrology》2013,165(4):663-682

Phenocryst assemblages of lavas from the long-lived Aucanquilcha Volcanic Cluster (AVC) have been probed to assess pressure and temperature conditions of pre-eruptive arc magmas. Andesite to dacite lavas of the AVC erupted throughout an 11-million-year, arc magmatic cycle in the central Andes in northern Chile. Phases targeted for thermobarometry include amphibole, plagioclase, pyroxenes, and Fe–Ti oxides. Overall, crystallization is documented over 1–7.5 kbar (~25 km) of pressure and ~680–1,110 °C of temperature. Pressure estimates range from ~1 to 5 kbar for amphiboles and from ~3 to 7.5 kbar for pyroxenes. Pyroxene temperatures are tightly clustered from ~1,000–1,100 °C, Fe–Ti oxide temperatures range from ~750–1,000 °C, and amphibole temperatures range from ~780–1,050 °C. Although slightly higher, these temperatures correspond well with previously published zircon temperatures ranging from ~670–900 °C. Two different Fe–Ti oxide thermometers (Andersen and Lindsley 1985; Ghiorso and Evans 2008) are compared and agree well. We also compare amphibole and amphibole–plagioclase thermobarometers (Ridolfi et al. 2010; Holland and Blundy 1994; Anderson and Smith 1995), the solutions from which do not agree well. In samples where we employ multiple thermometers, pyroxene temperature estimates are always highest, zircon temperature estimates are lowest, and Fe–Ti oxide and amphibole temperature estimates fall in between. Maximum Fe–Ti oxide and zircon temperatures are observed during the middle stage of AVC activity (~5–3 Ma), a time associated with increased eruption rates. Amphibole temperatures during this time are relatively restricted (~850–1,000 °C). The crystal record presented here offers a time-transgressive view of an evolving, multi-tiered subvolcanic reservoir. Some crystals in AVC lavas are likely to be true phenocrysts, but the diversity of crystallization temperatures and pressures recorded by phases in individual AVC lavas suggests erupting magma extensively reams and accumulates crystals from disparate levels of the middle to upper crust.  相似文献   

Melt production during granulite-facies anatexis: experimental data from “primitive” metasedimentary protoliths   总被引：11，自引：0，他引：11  

Gary Stevens  John D. Clemens  Giles T. R. Droop 《Contributions to Mineralogy and Petrology》1997,128(4):352-370

We conducted fluid-absent partial melting experiments, at 0.5 and 1.0?GPa in the temperature range 750 to 1000?°C, to investigate the influence of bulk rock Mg ? [100Mg/(Mg+Fe)] and the effects of additional TiO₂ on the granulite-grade anatectic evolution of relatively magnesian metapelites and metagreywackes. In these experiments, melting began between 780 and 830?°C by the incongruent breakdown of biotite to produce quartz-saturated, granulite-facies residual mineral assemblages in equilibrium with H₂O-undersaturated granitic melt. The glass (quenched melt) compositions produced in this study vary little. Generally, the glasses have compositions similar to those of many natural strongly peraluminous leucogranites. The solidus temperatures in both rock types increase with increasing Mg ?, but are unaffected by the presence or absence of a TiO₂ component. At 0.5?GPa the metapelites melted at temperatures up to 50?°C lower than the equivalent metagreywackes, but at 1?GPa there was no discernible difference. This study suggests that the fluid-absent solidus has a steep positive dP/dT slope in metapelites and steep negative dP/dT slope in metagreywackes. The pattern of melt production with increasing temperature is strongly controlled by the upper limit of biotite stability. In TiO₂-free compositions this was found to increase by 15 to 20?°C in the metapelites and by 30 to 40?°C in the metagreywackes, as a function of increasing Mg ? from 49 to 81. The presence of a TiO₂ component increases the upper limit of biotite stability by ～50?°C in the metapelites and by ～80?°C in the metagreywackes, over that observed in the equivalent TiO₂-free compositions. In consequence, in the TiO₂-free samples large pulses of melt (up to 35 wt%) are produced over narrow temperature ranges (as little as 15?°C in these experiments) between 830 and 875?°C. In the TiO₂-bearing samples the major pulse of melt production occurs more gradually between 830 and >900?°C.  相似文献   

Diurnal rainfall variations at Thessaloniki,Greece     

B. D. Giles  A. A. Flocas 《Theoretical and Applied Climatology》1990,41(4):221-225

Summary Hourly precipitation amounts recorded at the Aristotelian University of Thessaloniki for the period 1947–1985 are analysed. The contributions of each hour towards the annual, seasonal, and monthly mean diurnal variations are discussed and possible causes outlined. The probabilities of measurable precipitation occurring at any particular hour in a month and the importance of such a statistic to the tourist industry are noted.With 5 Figures  相似文献   

STRUCTURE AND ROTATION OF THE SOLAR INTERIOR: INITIAL RESULTS FROM THE MDI MEDIUM-L PROGRAM     

Kosovichev  A. G.  Schou  J.  Scherrer  P. H.  Bogart  R. S.  Bush  R. I.  Hoeksema  J. T.  Aloise  J.  Bacon  L.  Burnette  A.  De Forest  C.  Giles  P. M.  Leibrand  K.  Nigam  R.  Rubin  M.  Scott  K.  Williams  S. D.  Basu  Sarbani  Christensen-dalsgaard  J.  DÄppen  W.  Duvall  T. L.  Howe  R.  Thompson  M. J.  Gough  D. O.  Sekii  T.  Toomre  J.  Tarbell  T. D.  Title  A. M.  Mathur  D.  Morrison  M.  Saba  J. L. R.  Wolfson  C. J.  Zayer  I.  Milford  P. N. 《Solar physics》1997,170(1):43-61

The medium-l program of the Michelson Doppler Imager instrument on board SOHO provides continuous observations of oscillation modes of angular degree, l, from 0 to 300. The data for the program are partly processed on board because only about 3% of MDI observations can be transmitted continuously to the ground. The on-board data processing, the main component of which is Gaussian-weighted binning, has been optimized to reduce the negative influence of spatial aliasing of the high-degree oscillation modes. The data processing is completed in a data analysis pipeline at the SOI Stanford Support Center to determine the mean multiplet frequencies and splitting coefficients. The initial results show that the noise in the medium-l oscillation power spectrum is substantially lower than in ground-based measurements. This enables us to detect lower amplitude modes and, thus, to extend the range of measured mode frequencies. This is important for inferring the Sun's internal structure and rotation. The MDI observations also reveal the asymmetry of oscillation spectral lines. The line asymmetries agree with the theory of mode excitation by acoustic sources localized in the upper convective boundary layer. The sound-speed profile inferred from the mean frequencies gives evidence for a sharp variation at the edge of the energy-generating core. The results also confirm the previous finding by the GONG (Gough et al., 1996) that, in a thin layer just beneath the convection zone, helium appears to be less abundant than predicted by theory. Inverting the multiplet frequency splittings from MDI, we detect significant rotational shear in this thin layer. This layer is likely to be the place where the solar dynamo operates. In order to understand how the Sun works, it is extremely important to observe the evolution of this transition layer throughout the 11-year activity cycle.  相似文献