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11.
Mickey Man-Kui Wai 《Boundary-Layer Meteorology》1987,40(3):241-267
A one-dimensional grid-level model including longwave radiative transfer and a level-4 second-order turbulent transfer closure which contains prognostic equations for turbulent quantities, is used to study the physics and dynamics of inversion-capped marine stratocumulus clouds.A set of numerical experiments had been performed to examined the role of sea surface temperature, large-scale vertical velocity, wind speed, and vertical wind shear in the formation and the structure of low-level clouds. For a given sea surface and geostrophic wind speed, stratocumulus clouds can grow higher with smaller large-scale subsidence as less dry air entrains into the cloud. Clouds grow higher with higher sea surface temperature for a given geostrophic wind speed and large-scale subsidence as a result of enhanced moist convection. In high wind speeds, the entire cloud deck is lifted up because of larger surface energy flux. In the budget studies of the turbulent kinetic energy (TKE), the buoyancy term is a major source term when the wind speed and the vertical shear are small across the inversion top. When the wind speed and the vertical wind shear across the inversion top become large, the mixed layer is decoupled into a cloud and a subcloud layer. In the TKE budget studies, the shear generation term becomes an important term in the budgets of the TKE and the variance of vertical velocity. 相似文献
12.
Analysis of sediment samples collected from the Coeur d'Alene River in northern Idaho, USA, indicates that the main stem and
the south fork of the river are contaminated with heavy metals (Cd, Pb, Mn, and Zn) from the local mining operations. Laboratory
experiments indicate that these metals in the sediments can be leached and reach saturation concentrations in water in a relatively
short period of time. The rate of leaching of heavy metals with distilled water appeared to follow first-order kinetics. The
saturation concentrations of Mn and Zn in water reached ppm levels from the leaching process. Cadmium and Pb are much less
soluble relative to Zn in the sediments. The high concentrations of heavy metals in the sediments are a source of contamination
that should be considered for the water quality management planning of the Coeur d'Alene River-Lake system. 相似文献
13.
Brendan?P.?Kelaher Jeffrey?S.?LevintonEmail author Jamina?Oomen Bengt?J.?Allen Wai?Hing?Wong 《Estuaries and Coasts》2003,26(6):1505-1516
We studied changes in macrobenthic communities following the environmental clean-up of metal-polluted (cadmium, nickel, and
cobalt) sediments in Foundry Cove, a small inlet within the Hudson River estuary of New York. We used a BACI-style experiment
to test the hypotheses that high levels of cadmium in sediments change macrobenthic assemblages relative to unpolluted areas,
and removal of metals (especially cadmium) by dredging will restore the benthos, such that benthic fauna in Foundry Cove are
not different from unpolluted areas. In 1984, prior to the restoration work, there were no significant differneces between
macrobenthic assemblages in polluted and unpolluted locations, indicating that cadmium had little effect on community structure.
The lack of an observed toxicity effect may have been caused by the compensatory evolution of resistance to cadmium in dominant
organisms. Six years after the restoration work and despite a substantial reduction in metal pollution, there were lower abundances
of oligochaetes, nematodes, and chironomids and a higher abundance of polychaetes at Foundry Cove relative to reference locations.
Correlative analyses identified greater sediment compaction caused by dredging at Foundry, Cove as a possible cause of faunal
differences. The results demonstrate that it is difficult to accurately predict, the effects of anthropogenic disturbances
and restorations in complex natural systems and that unforeseen side effects are inevitable. Documenting these unpredicted
effects and experimentally understanding their causes in past restorations will greatly improve the success and cost-effectiveness
of future projects of a similar type. 相似文献
14.
Hazards caused by mass movement cost many human lives and cause severe damage to property. Accurate zonation of such hazards provides an important tool for preventive measures. Previous approaches for mass movement hazard zonation are costly because they require large amounts of data, time and labor, and are only applicable to specific local areas. In this paper, a Rapid Zonation of Abrupt Mass-movement Hazard (RZAMH), applicable to large regions, is proposed. It involves the selection of appropriate zonation principles, routes, units, and indexes that can be used for the classification of reference groups, identification of matching groups of test sites, evaluation of blank test sites, and coalescence of sub-regions into specified zonation areas. The K-means clustering method is used in the classification processes. The applicability of the RZAMH approach to a large area implies that the number of reference sites required to build the reference groups is not of primary importance as long as the reference sites are representative. Therefore, for large areas, the RZAMH approach would be more economical than other conventional methods. The RZAMH approach is probably applicable to all abrupt mass movement hazards including rock falls, landslides, and debris flows. 相似文献
15.
Significant insight into the dynamic local site response of a horizontally layered sediment deposit to seismic excitation
can be gained from numerical simulations. In this paper we use a nonlinear local site response analysis code SPECTRA to estimate
the coseismic sediment deformation at a seismically active site in Lotung, Taiwan. We address some basic issues relevant for
interpreting the simulation results, including the impact of noise and baseline offsets present in the input ground motion.
We also consider the sensitivity of the predicted deformation responses to statistical variations of sediment constitutive
properties. Finally, we apply a suite of hypothetical strong ground motions to the base of the sediment deposit to better
understand the pattern of inelastic deformation likely to result from strong seismic shaking. 相似文献
16.
多向不规则波绕射的数值模拟 总被引:9,自引:1,他引:8
采用有限元求解Boussinesq方程数值计算模型,对单突堤和双突堤的波浪绕射进行了数值模拟,并与物模试验进行对比验证。模拟结果表明入射波浪的方向分布对波浪的绕射具有明显的影响,使防波堤后的波浪增大,开阔区域的浪浪减小,波浪的方向分布对港内波浪的分布具有一定的均化作用。 相似文献
17.
The problem of wild elephants, or human-elephant conflict (HEC), influences the daily life of local communities and hinders the conservation of wild elephants.The perception and attitudes of local communities who inhabited the frontiers between human activities and wild elephant movement are important to the mitigation of the HEC and conservation of wild elephants. To analyze the perception and attitudes of local communities, the Participatory Rural Appraisal (PRA) was used in the investigation of 423 interviewees from 22 villages in Xishuangbanna from July 2009 to February 2010. The results indicated that local communities had their views on the elephant-related problems. In field survey, we found that 66.5% of interviewees were willing to support, participate in, and assist in the conservation of wild elephants;33.5% of interviewees were opposed or indifferent to such conservation, because their livelihoods and even their lives were endangered by wild elephants. These views and attitudes were influenced by local communities′perception of HEC, education level, gender and self-interest. Therefore, it is necessary to analyze the diverse views among local communities and balance profits and costs in addressing HEC. 相似文献
18.
19.
Seasonal movement and groundwater flow mechanism in an unsaturated saprolitic hillslope 总被引:4,自引:4,他引:0
Numerous field monitoring programs have been conducted to investigate the performance of an unsaturated soil slope subjected to rainfalls in wet seasons. Most case histories focus on the response of matric suction, which is one of the two stress-state variables governing unsaturated soil behaviour. However, effects due to another variable, net normal stress, are often ignored. Also, slope performance under alternative wet and dry seasons is rarely reported and analysed. In this study, a saprolitic hillslope situated in Hong Kong was instrumented heavily to investigate its seasonal movement due to changes of the two variables and also groundwater flow mechanism. Two-year seasonal variations of matric suction and net normal stress were monitored by tensiometers together with heat dissipation matric water potential sensors and earth pressure cells, respectively. During heavy rainstorms in wet season, there was a substantial recharge of the main groundwater table, causing a significant increase of positive pore-water pressure in deeper depths. Rupture surface likely developed at depths between 5.5 and 6 m, hence resulting in a “deep-seated” mode of downslope movement. The downslope movement resulted in a peak increase of horizontal stress. In dry seasons, matric suction of up to 190 kPa was recorded, and the associated soil shrinkage led to substantial upslope rebounds. The stress built up in wet seasons hence reduced. After monitoring period of 2 years, downslope ratcheting is identified. Up to 40 % of the downslope displacements were recovered by the upslope rebounds. 相似文献
20.
A plant is stabilized by its root system. In congested urban cities such as Hong Kong, ground trenching is frequently seen due to the installation of utility lines along the roadside. Soil nailing, which involves soil coring in slopes, is a common solution to improve the slope stability. However, both activities inevitably pose a risk to the integrity of any root systems present, and thus reduce the root anchorage. To prevent or minimize such damage, a careful design of the excavation/drilling location is of prime importance. Ground penetrating radar (GPR) provides a non-destructive method for locating roots by examining the contrast between the dielectric properties of the roots and the surrounding soil. To examine the performance of GPR and promote its use in Hong Kong, a test bed was prepared using local materials to create a controlled environment in which to conduct a series of systematic tests evaluating the performance of a 900 MHz GPR. The reflected radargrams were subject to the influence of the following factors: size and depth of roots, horizontal distance between roots, and contrast between the root and soil water content. Correlations between root size and a number of waveform parameters were also explored. Limiting values for root size, root embedded depth, horizontal separation distance between roots, and water content contrast between root and soil were obtained. A significant correlation was found between the root diameter and time travel parameter T 2 (p<0.001, r=0.795). Because GPR root detection is highly site-specific, this study provides a local reference for GPR performance in the Hong Kong environment. The findings demonstrate that the 900 MHz GPR is applicable in Hong Kong for the detection of main roots. 相似文献