Professor Sir Nicholas Shackleton     

PHILIP GIBBARD 《Boreas: An International Journal of Quaternary Research》2006,35(2):385-390

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BLENDING HEIGHTS FOR WINDS OBLIQUE TO CHECKERBOARDS     

J. R. PHILIP 《Boundary-Layer Meteorology》1997,82(2):263-281

Analysis of the two-dimensional checkerboardproblem of many alternating surfaces with different properties andvarious scales and aspect ratios is extended to the general case ofwinds oblique to the surface pattern. Relevant periodic solutions ofa three-dimensional atmospheric convection-diffusion equation arefound, and used to estimate blending heights for both concentrationand flux.Illustrative results show negligible directional effect on blendingheight for X1* (the smaller pattern wavelength) of 10 m, but a ratio of maximum/minimum heights of about 3 to 5 for X1* = 100 m. For X1* = 1000 mthe directional variation is strongly peaked with a maximum/minimum ratio of 8 to 14. At fixed X1* the maximum increases with check aspect ratio. It is associated withthe case where the wind blows along one check diagonal. In thatsingular situation, damping of the dominant harmonic varying normalto the diagonal depends purely on transverse and vertical diffusion:horizontal convection and wind shear play no part.  相似文献   

Identification of Permian palaeowind direction from wave-dominated lacustrine sediments (Lodève Basin, France)     

STÉPHANE POCHAT  JEAN VAN DEN DRIESSCHE  VALÉRIE MOUTON  FRANÇOIS GUILLOCHEAU 《Sedimentology》2005,52(4):809-825

Lacustrine environments are an excellent indicator of continental palaeoclimate. In particular, the sedimentary record of waves in lakes may be used to constrain atmospheric palaeocirculation. Wave ripples have been identified in a Permian lacustrine basin (the Salagou Formation, 260–250 Ma, Lodève Basin) located in the southern French Massif Central, part of the western European Hercynian mountain chain. Wave ripple patterns are interpreted with regards to hydrodynamics and water palaeodepth. It is shown that, in the case of the Salagou Formation, wave ripple orientations were controlled by the direction of the prevailing palaeowind. The Late Permian wind blew from between north and 20° east of north, possibly over several millions of years and certainly throughout the period of deposition of about 2000 m of strata in the Lodève Basin. Permian lacustrine sedimentation is widespread and well preserved on the Earth's surface and so wave ripple data may help constrain numerical modelling of the Earth's past climates, especially with regards to Permian times outside of desert regions.  相似文献   

Dating the onset of Lower Tagus River terrace formation using electron spin resonance          下载免费PDF全文

PIERLUIGI ROSINA  PIERRE VOINCHET  JEAN‐JACQUES BAHAIN  JORGE CRISTOVÃO  CHRISTOPHE FALGUÈRES 《第四纪科学杂志》2014,29(2):153-162

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Coagulation and transport of sediments in the Gironde Estuary   总被引：3，自引：0，他引：3  

R. J. GIBBS  D. M. TSHUDY  L. KONWAR  JEAN MARIE MARTIN† 《Sedimentology》1989,36(6):987-999

The distribution of suspended particle size and concentration were measured along the Gironde Estuary, France, from the river seaward to the ocean. The suspended particle size and volume concentration were measured using in situ holography and onboard optical techniques utilizing special procedures in order to avoid floc breakage. Sediments discharged by the rivers coagulate upon encountering the very low salinities (0.2‰ of the upper estuary (confirmed with laboratory experiments), and are then transported and deposited by currents in the remainder of the estuary. This coagulation, coupled with estuarine circulation, produces a turbidity maximum which is offset between the surface and bottom waters. The floc size maximum is oceanward of the turbidity maximum and is, likewise, offset along the estuary by about 30 km. The estuary can be subdivided into the following zones: (1) coagulation; (2) hydrodynamic, landward of the null point; and (3) hydrodynamic, seaward of the null point. Initial coagulation appears to be completed in coagulation zone (1), and particles are transported and settled (with very little floc breakage and recoagulation) in zones (2) and (3) only. The floc settling velocities, coupled with estuarine circulation, control the concentration and size distributions of flocs in the water column, and eventually control the deposition of sediments.  相似文献   

Sediment suspension under waves and currents: time scales and vertical structure     

PHILIP D. OSBORNE  BRIAN GREENWOOD 《Sedimentology》1993,40(4):599-622

Field measurements of the vertical structure of near-bed suspended sediment concentrations were obtained from arrays of fast response optical backscatter suspended solids sensors to examine the time-dependent response of sediment resuspension to waves and currents and the constraints imposed by bedforms. Data were recorded from both a nonbarred, marine shoreface and a barred lacustrine shoreface, under both shoaling and breaking waves (significant heights of 0·25–1·50m; peak periods of 3 and 8 s) and in water depths of 0·5–5·0 m. Sediment concentrations are positively correlated with increasing elevation above the bed, but lagged in time. The time lag varies directly with separation distance between measurement locations and inversely with the horizontal component of the near-bed oscillatory velocity. Both the presence of wave groups and the settling velocities of the sediment particules in suspension influence the temporal changes in concentration at a given elevation. Sediment concentrations appear to respond more slowly to the incident wind-wave forcing with distance away from the bed as a result of two factors: (1) the sequential increase in concentration induced by a succession of large waves in a group; and (ii) the relative increase in finer sediments with smaller settling velocities. Bedforms interact with the near-bed horizontal currents to impose a distinct constraint upon the timing of suspension events relative to the phase of the fluid motion, and, therefore, the vertical structure of the suspended sediment concentration at a range of time scales. The near-bed concentrations appear to be strongly dependent upon the vertical convection of sediment associated with the ejection from the wave boundary layer of separation vortices generated in the lee of ripple crests. Concentration gradients in the presence of vortex ripples are large, as are the correlation between concentrations measured at different elevations within the fluid.  相似文献   

Flow speed and calving rate of Kongsbreen glacier, Svalbard, using SPOT images   总被引：2，自引：0，他引：2  

BERNARD LEFAUCONNIER  JON OVE HAGEN  JEAN PAUL RUDANT 《Polar research》1994,13(1):59-65

Kongsbreen, a tide-water glacier located in Kongsfjorden, is the most active calving glacier in Svalbard. Three SPOT images are used to determine its flow speed and calving rate. The position of fourteen reference points was determined on the coast or mountain sides, and the changes in position of 144 characteristic features on the glacier surface were calculated. The obtained speed profiles arc consistent with the findings from previous works from 1962-64 and 1983-86. When comparing the obtained longitudinal profile to the data from 1962–64. it is found that the flow velocity at a given distance from the front has been nearly constant.
The results from the SPOT images analysis are completed by using existing topographic works. The present study shows that SPOT images (panchromatic as well as multichannel), recorded with a periodicity of one year, can be used to determine precisely the annual flow speed and calving rate of active glaciers such as Kongsbreen. Images recorded with a periodicity of two, three or four weeks can allow identical determination on tide-water glaciers during a surging active phase.  相似文献   

ENHANCED MIGRATION OF SEISMIC DATA1     

PHILIP M. CARRION 《Geophysical Prospecting》1990,38(7):689-704

The so-called ‘enhanced migration’ which uses diffraction tomography as the ‘repair tool’ for correction of amplitudes (reflection coefficients) of migrated sections is discussed. As with any linearized procedure, diffraction tomography requires knowledge of the initial model. It is suggested that the initial model is taken as the migrated image. It will be demonstrated that diffraction tomography applied to the data residuals improves the amplitudes of the migrated images. Migration is redefined as the reconstruction of the wavefront sets of distributions (reflection interfaces), and the inversion process as tomographic correction of migrated images.  相似文献   

Pressure--Temperature--Time Paths of Regional Metamorphism I. Heat Transfer during the Evolution of Regions of Thickened Continental Crust   总被引：5，自引：0，他引：5  

ENGLAND  PHILIP C.; THOMPSON  ALAN BRUCE 《Journal of Petrology》1984,25(4):894-928

The development of regional metamorphism in areas of thickenedcontinental crust is investigated in terms of the major controlson regional-scale thermal regimes. These are: the total radiogenicheat supply within the thickened crust, the supply of heat fromthe mantle, the thermal conductivity of the medium and the lengthand time scales of erosion of the continental crust. The orogenicepisode is regarded as consisting of a relatively rapid phaseof crustal thickening, during which little temperature changeoccurs in individual rocks, followed by a lengthier phase oferosion, at the end of which the crust is at its original thickness.The principal features of pressure—temperature—time(PTt) paths followed by rocks in this environment are a periodof thermal relaxation, during which the temperature rises towardsthe higher geotherm that would be supported by the thickenedcrust, followed by a period of cooling as the rock approachesthe cold land surface. The temperature increase that occursis governed by the degree of thickening of the crust, its conductivityand the time that elapses before the rock is exhumed sufficientlyto be affected by the proximity of the cold upper boundary.For much of the parameter range considered, the heating phaseencompasses a considerable portion of the exhumation (decompression)part of the PTt path. In addition to the detailed calculationof PTt paths we present an idealized model of the thickeningand exhumation process, which may be used to make simple calculationsof the amount of heating to be expected during a given thickeningand exhumation episode and of the depth at which a rock willstart to cool on its ascent path. An important feature of thesePTt paths is that most of them lie within 50 °C of the maximumtemperature attained for one third or more of the total durationof their burial and uplift, and for a geologically plausiblerange of erosion rates the rocks do not begin to cool untilthey have completed 20 to 40 per cent of the total uplift theyexperience. Considerable melting of the continental crust isa likely consequence of thickening of crust with an averagecontinental geotherm. A companion paper discusses these resultsin the context of attempts to use metamorphic petrology datato give information on tectonic processes.  相似文献   

Pressure--Temperature--Time Paths of Regional Metamorphism II. Their Inference and Interpretation using Mineral Assemblages in Metamorphic Rocks   总被引：1，自引：0，他引：1  

THOMPSON  ALAN BRUCE; ENGLAND  PHILIP C. 《Journal of Petrology》1984,25(4):929-955

A companion paper (England & Thompson, 1984a) investigatesthe pressure-temperature-time (PTt) paths followed by rocksundergoing burial metamorphism in continental thickening events.This paper discusses problems involved in inferring such pathsfrom the petrological data available in metamorphic rocks and—oncesuch paths are determined—how they may be interpretedin terms of the thermal budgets of metamorphism. Each of theprincipal facies series (glaucophane-jadeite, andalusite- sillimaniteand kyanite-sillimanite) may be encountered by rocks involvedin the thickening and erosion of continental crust in a regimeof average continental heat flow. The inference of a minimumthermal budget required for a given metamorphism depends stronglyon a knowledge of the PTt paths followed by rocks during themetamorphism. Discrimination between possible thermal regimesis greatly enhanced if portions of PTt paths, rather than singlePT points, are available, and additional constraint is possibleif these paths are supplemented by geochronological, structuraland heat flow data.  相似文献