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31.
Rory O. R. Y. Thompson 《Boundary-Layer Meteorology》1974,6(3-4):515-518
A Simple slab model of the planetary boundary layer is extended to include vertical shear of the geostrophic wind. The layer depth is assumed to be determined by a Richardson number criterion. The cross-isobar angle for the surface wind is given in terms of the drag coefficient, the Froude number of the layer, and the angle between the thermal wind and the surface isobars. The theoretical results resemble the observations rather well. 相似文献
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We present N-body simulations of planetary accretion beginning with 1 km radius planetesimals in orbit about a 1 M⊙ star at 0.4 AU. The initial disk of planetesimals contains too many bodies for any current N-body code to integrate; therefore, we model a sample patch of the disk. Although this greatly reduces the number of bodies, we still track in excess of 105 particles. We consider three initial velocity distributions and monitor the growth of the planetesimals. The masses of some particles increase by more than a factor of 100. Additionally, the escape speed of the largest particle grows considerably faster than the velocity dispersion of the particles, suggesting impending runaway growth, although no particle grows large enough to detach itself from the power law size-frequency distribution. These results are in general agreement with previous statistical and analytical results. We compute rotation rates by assuming conservation of angular momentum around the center of mass at impact and that merged planetesimals relax to spherical shapes. At the end of our simulations, the majority of bodies that have undergone at least one merger are rotating faster than the breakup frequency. This implies that the assumption of completely inelastic collisions (perfect accretion), which is made in most simulations of planetary growth at sizes 1 km and above, is inappropriate. Our simulations reveal that, subsequent to the number of particles in the patch having been decreased by mergers to half its initial value, the presence of larger bodies in neighboring regions of the disk may limit the validity of simulations employing the patch approximation. 相似文献
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This study examined water quality in the upper Animas River watershed, a mined watershed that gained notoriety following the 2015 Gold King mine release of acid mine drainage to downstream communities. Water-quality data were used to evaluate trends in metal concentrations and loads over a two-decade period. Selected sites included three sites on tributary streams and one main-stem site on the Animas River downstream from the tributary confluences. During the study period, metal concentrations and loads varied seasonally and annually because of hydrologic variability and remedial actions designed to ameliorate the effects of acid mine drainage. Water-quality data were divided into two periods based on the timing of remedial activities in the watershed. The first period includes active water treatment, surface reclamation and installation of bulkheads in adits; the second period includes the decade following these activities. Water-quality data were used to estimate annual and monthly zinc loads using the Adjusted Maximum Likelihood Method (using LOADEST software) and U.S. Geological Survey streamflow data. This study presents one of the first applications of LOADEST focused on metal loads. Monthly flow-weighted concentrations were analysed using a Mann-Kendall trend test to determine the direction, magnitude, and significance of temporal trends in zinc loading in any given month and using t-test comparisons between the two periods. Zinc loads estimated for the Animas River below the tributaries indicate decreased zinc loading during the rising limb of the hydrograph in the second period, perhaps reflecting a reduction of snowmelt-derived zinc load following surface reclamation activities. In contrast, base-flow zinc loading increased at the main-stem site, perhaps because of the cessation of water treatment in tributary streams. Flow weighting of monthly load estimates yielded increased statistical significance and enabled more nuanced differentiation between the effects of hydrologic variability and remedial activities on zinc loading. 相似文献
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Patterns of soil water repellency change with wetting and drying: the influence of cracks,roots and drainage conditions 
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下载免费PDF全文 Laboratory experiments were used to investigate the influence of simulated cracks and roots on soil water repellency (SWR) dynamics with and without basal drainage impedance in wetting–drying cycles. Observations and measurements were taken following water application equivalent to 9.2‐mm rainfall and then periodically during 80 h of drying. In total, 180 experiments were carried out using 60 samples of three homogeneous, reconstituted soils with different organic matter contents and textures, but of similar initial severity of SWR [18% molarity of an ethanol droplet (MED)]. Water flowing down the cracks and roots left the soil matrix largely dry and water repellent except for vertical zones adjacent to them and a shallow surface layer. A hydrophilic shallow basal layer was produced in experiments where basal drainage was impeded. During drying, changes in SWR were largely confined to the zones that had been wetted. Soil that had remained dry retained the initial severity of SWR, while wetted soil re‐established either the same or slightly lower severity of SWR. In organic‐rich soil, the scale of recovery to pre‐wetting MED levels was much higher, perhaps associated with temporarily raised levels (up to 36% MED) of SWR recorded during drying of these soils. With all three soils, the re‐establishment of the original SWR level was less widespread for surface than subsurface soil and with impeded than unimpeded basal drainage. Key findings are that as follows: (1) with unimpeded basal drainage, the soils remained at pre‐wetting repellency levels except for a wettable thin surface layer and zones close to roots and cracks, (2) basal drainage impedance produced hydrophilic basal and surface layers, (3) thorough wetting delayed a return to water‐repellent conditions on drying, and (4) temporarily enhanced SWR occurred in organic‐rich soils at intermediate moisture levels during drying. Hydrological implications are discussed, and the roles of cracks and roots are placed into context with other influences on preferential flow and SWR under field conditions. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Rory Mortimore 《Proceedings of the Geologists' Association. Geologists' Association》2011,122(2):232-297
Inversion tectonic episodes are identified in the Upper Turonian - Lower Coniacian, Santonian - Lower Campanian and later Lower Campanian Chalk. It is suggested that episodic tectonism created the seabed topography on which sea levels and erosional currents acted. Marked differentiation into linear belts of local basins and swells with a greater variety of sediments is present in the Santonian and Lower Campanian. During this same period the locus of sedimentation shifts westwards from the southern margin of the Weald to Wessex as Weald Basin inversion increases. Tectonic episodes also produced synsedimenary fracturing of the Chalk and evolution of vein networks and stylolytes. Upper Cretaceous tectonic and sea-level events also affected the platform of Europe, the Carpathians and the Syrian Arc where sedimento-tectonic scenarios provide analogues for the Chalk. Linking sea-level oscillations and tectonic episodes with microtectonic studies suggests a frequency of events within the range of 0.35-1.5 Ma. 相似文献
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We present early to Mid‐Holocene paleo‐geographic reconstructions for the Ramore Head area (Northern Ireland). This coastal area is characterized by Mesolithic occupation (c. 10–6 ka) and preserved early–Mid‐Holocene peats both on‐ and offshore. This paper improves on previous reconstructions by employing a backstripping methodology, which removes accumulated recent deposits from identified buried paleo‐landsurfaces instead of using modern topography as an analogue to the past landscape. Paleo‐landsurfaces are identified offshore from seismic profiles supplemented by cores, and onshore through legacy borehole records. The paleo‐landsurface can be traced offshore to depths of −2 to −19 m and is buried by <5 m of modern sediment. It extends onshore under the coastal town of Portrush and is buried <2.5–10 m below modern ground level. The identified paleo‐landsurface is combined with sea‐level curves from recent Glacio‐Isostatic‐Adjustment models to reconstruct marine transgression during the early–Mid‐Holocene. Comparison is also made with reconstructions based on modern topography. Together, the identified paleo‐landsurfaces and revised reconstructions can assist future site prospection on‐ and offshore and delimit high‐potential areas for heritage management. Revised reconstructions also allow placement of extant archaeology into a more accurate context of landscape change and help develop insights into local‐scale site location patterns. 相似文献
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Rory N. Mortimore 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(3):392-420
Late Cretaceous sedimentary history has been strongly influenced by both sea-level fluctuations and inversion tectonics. Evidence for tectonic movements, originally identified in German Late Cretaceous basins, is applied to the UK successions. Two periods of movement are conspicuous: a Middle Turonian episode involving huge loss of section along anticlinal axes in southern England and a Late Santonian-Early Campanian episode also involving section loss on structure and section gain off structure. This pattern is repeated where folds or blocks are underlain by inversion thrust faults (e.g. the Purbeck Fault in Dorset, the Falmer Fault in Sussex, the Portsdown Fault in Hampshire and the Bray Fault in Upper Normandy). Other episodes of inversion in the Late Turonian to Middle Coniacian and the late Early Campanian are investigated and are a probable cause of slump beds and slides. These tecto-sedimentary episodes can be applied to structures in Northern Ireland, Inner Hebrides, North Sea and Yorkshire as well as southern Britain. Beyond NW Europe the Late Santonian – Early Campanian event is widely recognised in the Carpathians, southern Europe, Africa and the Levant and coincides with the end of the Long Cretaceous Quiet Zone (Chron 34N to 33R) perhaps representing a major change in Earth dynamics related to Mid-Ocean Ridge crustal production and intra-continental crust tectonism. 相似文献
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AbstractA simple model is given that describes the response of the upper ocean to an imposed wind stress. The stress drives both mean and turbulent flow near the surface, which is taken to mix thoroughly a layer of depth h, and to erode the stably stratified fluid below. A marginal stability criterion based on a Froude number is used to close the problem, and it is suggested that the mean momentum has a strong role in the mixing process. The initial deepening is predicted to obeywhere u. is the friction velocity of the imposed stress, N the ambient buoyancy frequency, and t the time.After one-half inertial period the deepening is arrested by rotadeon at a depth h = 22/4 u.{(Nf)+ where f is the Coriolis frequency. The flow is then a “mixed Ekman” layer, with strong inertial oscillations superimposed on it. Three quarters of the mean energy of the deepening layer is found to be kinetic, and only one-quarter potential.Heating and cooling are included in the model, but stress dominates for time-scales of a day or less. Non-uniform stratification and currents existing prior to the onset of the wind are easily included.Agreement between the first formula above and laboratory experiments of Kato and Phillips is very satisfactory; the second formula is consistent with observations of Francis and Stommel, though a more thorough test is needed. Oceanic observations in general support the assumption of slab-like mean profiles and direct response of the fluid to local winds. 相似文献
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