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Philippe Machetel 《Comptes Rendus Geoscience》2003,335(1):91-97
The numerical models of mantle convection agree to depict avalanches behaviour according to the level of endothermicity of the spinel → perovskite phase change. Their potential effects on the global thermal and dynamical states of the mantle have been computed thanks to a numerical code, which takes into account both the 400-km exothermic and the 660-km endothermic phase changes. The cycle followed by the avalanches is: local layering, destabilization of the 660-km thermal layer, travelling and spreading on the core, and reappearing of the local layering. Therefore, mantle convection is characterized by quiet periods of partial layering embedded in catastrophic events. During the avalanche, the amplitude of the surface velocity is multiplied by two, which would imply an enhanced plate tectonic and ridge activities. The global thermal effects of the avalanche are compatible with a high mantle temperature and an acceleration of Earth's rotation during the Cretaceous. They also offer a coherent explanation to locate the origin of mantle plumes both within the CMB and just below the transition zone. 相似文献
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Ü. Rannik T. Markkanen J. Raittila P. Hari T. Vesala 《Boundary-Layer Meteorology》2003,109(2):163-189
Observations of wind statistics within and above a Scots pine forest are comparedwith those predicted from an analytical second-order closure model. The roughnesssublayer (RSL) effects, and the influence of stability on similarity functions, arestudied using observations. The commonly accepted forms of similarity functionsdescribe the influence of diabatic effects above the RSL well. According to earlierstudies they are expected also to apply within the RSL. As an exception, the averagewind speed normalised with friction velocity was found to be invariant with stabilityclose to the canopy top under unstable conditions. Lagrangian stochastic trajectorysimulations were used to evaluate the influence of canopy turbulence profiles onfootprint prediction. The main uncertainty was found to arise from parameterisationof the random forcing term in the Lagrangian velocity equation. The influence ofdiabatic conditions was studied, and it was found that thermal stability affectssignificantly the footprint function above the forest canopy, but significantuncertainty exists because of uncertainties in the formulation of stability functions. 相似文献
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A Simple Parameterisation for Flux Footprint Predictions 总被引:9,自引:6,他引:9
Flux footprint functions estimate the location and relative importance of passive scalar sources influencing flux measurements
at a given receptor height. These footprint estimates strongly vary in size, depending on receptor height, atmospheric stability,
and surface roughness. Reliable footprint calculations from, e.g., Lagrangian stochastic models or large-eddy simulations
are computationally expensive and cannot readily be computed for long-term observational programs. To facilitate more accessible
footprint estimates, a scaling procedure is introduced for flux footprint functions over a range of stratifications from convective
to stable, and receptor heights ranging from near the surface to the middle of the boundary layer. It is shown that, when
applying this scaling procedure, footprint estimates collapse to an ensemble of similar curves. A simple parameterisation
for the scaled footprint estimates is presented. This parameterisation accounts for the influence of the roughness length
on the footprint and allows for a quick but precise algebraic footprint estimation. 相似文献
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This paper presents the detailed results and analyses on the ecological footprints and bio-capacities of the individual cities and the province as a whole for the year 2001, providing a clear picture of sustainability for the province. Results show that the ecological footprints of most cities in Liaoning exceeded their respective bio-capacities, incurring high ecological deficits. The ecological deficit of the province as a whole was 1.31 ha/cap. Those cities with resources extraction and/or primary material-making as their major industries constitute the "ecologically black band", whose ecological deficits ranged from 2.45 to 5.23 ha/cap, the highest of all cities in the province. Fossil energy consumption was the major source of footprint amounting to 1.63 ha/cap at the provincial level, taking up 67.3% of the total. For cropland, modest ecological surpluses occurred in Jinzhou, Tieling, Huludao, and Panjin while modest ecological deficits in Dalian, Benxi, Fushun, and Dandong, resulting in an overall surplus for the province. Liaoning had a certain level of surplus in fishing ground (water area), mainly distributed in the coastal cities of Dalian, Panjin, Huludao, Yingkou, Jinzhou, and Dandong. Most cities had a small ecological deficit in pasture and all had a small ecological surplus in forest. The eco-efficiency, expressed as GDP value per hectare of footprint, exhibits high variations among the cities, with the highest (Shenyang) more than 10 times the lowest (Fuxin). Cities with manufacture, high-tech, and better developed service industries had high eco-efficiency, while those with resources extraction, primary material-making, and less developed service industries had low eco-efficiency. Based on the components and geographical distribution of ecological footprint, strategic policy implications are outlined for Liaoning's development toward a sustainable future. 相似文献
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生态足迹模型在山区生态可持续评价中的初步应用--以1999年北京西部山区为例 总被引:3,自引:0,他引:3
在剖析生态足迹分析法的理论基础上,进一步考虑不同消费水平对生态足迹时空变异的影响,划分农村居民和城镇居民两类不同的消费群体,分别计算各自的生态足迹,其次进一步细化模型中人均水资源足迹,从而构建生态足迹与生态容量平衡模型。根据平衡模型计算出生态盈亏,得出区域生态持续性评价结果。并以1999年北京西部山区门头沟区为例,进行模型计算和生态可持续评价,结果表明1999年门头沟区处于生态赤字状态,说明该区生态系统处于不可持续状态。在对门头沟区的初步研究基础上,指出生态足迹作为山区生态可持续评价指标的优点及当前存在的缺点。 相似文献
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基于生态足迹理论和计算模型,根据工业生产的特点,计算了1997-2007年重庆市人均工业生态足迹和万元工业产值的生态足迹,并与有关研究数据进行了对比分析.结果显示:重庆市的人均工业生态足迹约相当于全国平均水平,但已超出重庆市总的生态承载力,并呈现出持续上升趋势,工业生产处于生态不可持续状态;万元工业产值的生态足迹略低于全国平均水平,下降趋势明显.表明重庆市通过转变工业发展模式,在不降低生产能力的条件下,减少工业生态足迹大有作为. 相似文献
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中国不同区域能源消费碳足迹的时空变化(英文) 总被引:2,自引:2,他引:2
Study on regional carbon emission is one of the hot topics under the background of global climate change and low-carbon economic development, and also help to establish different low-carbon strategies for different regions. On the basis of energy consumption and land use data of different regions in China from 1999 to 2008, this paper established carbon emission and carbon footprint models based on total energy consumption, and calculated the amount of carbon emissions and carbon footprint in different regions of China from 1999 to 2008. The author also analyzed carbon emission density and per unit area carbon footprint for each region. Finally, advices for decreasing carbon footprint were put forward. The main conclusions are as follows: (1) Carbon emissions from total energy consumption increased 129% from 1999 to 2008 in China, but its spatial distribution pattern among different regions just slightly changed, the sorting of carbon emission amount was: Eastern China > Northern China > Central and Southern China > Southwest China > Northwest China. (2) The sorting of carbon emission density was: Eastern China > Northeast China > Central and Southern China > Northern China > Southwest China > Northwest China from 1999 to 2003, but from 2004 Central and Southern China began to have higher carbon emission density than Northeast China, the order of other regions did not change. (3) Carbon footprint increased significantly since the rapid increasing of carbon emissions and less increasing area of pro-ductive land in different regions of China from 1999 to 2008. Northern China had the largest carbon footprint, and Northwest China, Eastern China, Northern China, Central and Southern China followed in turn, while Southwest China presented the lowest area of carbon footprint and the highest percentage of carbon absorption. (4) Mainly influenced by regional land area, Northern China presented the highest per unit area carbon footprint and followed by Eastern China, and Northeast China; Central and Southern China, and Northwest China had a similar medium per unit area carbon footprint; Southwest China always had the lowest per unit area carbon footprint. (5) China faced great ecological pressure brought by carbon emission. Some measures should be taken both from reducing carbon emission and increasing carbon absorption. 相似文献