共查询到20条相似文献，搜索用时 31 毫秒
1.
J. Abaurrea J. Asín A. C. Cebrián 《Stochastic Environmental Research and Risk Assessment (SERRA)》2015,29(1):309-322
A joint model is proposed for analyzing and predicting the occurrence of extreme heat events in two temperature series, these being daily maximum and minimum temperatures. Extreme heat events are defined using a threshold approach and the suggested model, a non-homogeneous common Poisson shock process, accounts for the mutual dependence between the extreme events in the two series. This model is used to study the time evolution of the occurrence of extreme events and its relationship with temperature predictors. A wide range of tools for validating the model is provided, including influence analysis. The main application of this model is to obtain medium-term local projections of the occurrence of extreme heat events in a climate change scenario. Future temperature trajectories from general circulation models, conveniently downscaled, are used as predictors of the model. These trajectories show a generalized increase in temperatures, which may lead to extrapolation errors when the model is used to obtain projections. Various solutions for dealing with this problem are suggested. The results of the fitted model for the temperature series in Barcelona in 1951–2005 and future projections of extreme heat events for the period 2031–2060 are discussed, using three global circulation model trajectories under the SRES A1B scenario. 相似文献
2.
Caballero A Espino M Sagarminaga Y Ferrer L Uriarte A González M 《Marine pollution bulletin》2008,56(3):475-482
A main conclusion following the oil spill from the Prestige tanker was that improvements in ocean circulation models were necessary; this was in order to predict, more accurately, the trajectories followed by the oil slicks and hence assist in fight against oil pollution operations. In this contribution, the results of the validation of a semi-empirical ocean circulation model, parameterised for the Bay of Biscay and forced with operational oceano-meteorological remote sensing observations, are shown. The model results have been validated with observations from drifting buoys, deployed in the Bay of Biscay during the crisis. The results show that the model explains a relatively large percentage of the current variability. The comparisons between the real and the estimated drifter trajectories indicate that for 3, 5 and 7 day-long trajectories, the drifter position is estimated with errors of approximately 23, 35 and 46km, respectively. The model reproduces relatively well the trajectory followed by the drifter with the shortest period (23 days). 相似文献
3.
Three-component recordings permit the construction of particle trajectories. These three-dimensional pictures of particle motion show successive predominant directions of polarization and allow wave modes with distinct polarization directions to be recognized. A polarization selection, called ‘spatial directional filtering’, can be accomplished by several methods; four techniques are described. The application of these polarization filters to a noise shot, offset VSPs and CDP stack are also presented. This type of filtering is shown to cancel waves with undue polarization and to enhance the signal-to-noise ratio. 相似文献
4.
A study of the atmospheric circulation between equator and 60oN during the winter and summer seasons
Stefan L. Hastenrath 《Pure and Applied Geophysics》1969,77(1):207-226
Summary The mean zonal and meridional wind components and the mean mass circulation in different latitudes are discussed in relation to previous studies. Divergence and vertical motion are calculated for various latitude belts. There is evidence for a strong tropical Hadley cell with a temperate latitude indirect circulation during the winter season. During summer, the northern Hadley cell is weaker and displaced poleward; a circulation in the opposite sense appears in equatorial latitudes.The regional patterns of divergence and vertical motion appear related particularly to the position of the subtropical high pressure cells. Subsidence and lower-layer divergence are characteristic of the eastern flanks of the subtropical anticyclones, while the opposite pattern prevails on its western flanks. These longitudinal contrasts appear particularly pronounced during the summer season. The three-dimensional flow pattern in the tropics is illustrated by selected trajectories for the winter and summer seasons. 相似文献
5.
Taroh Matsuno 《Pure and Applied Geophysics》1980,118(1):189-216
Development of thoughts on tracer transport mechanisms in the stratosphere which lead to new approaches to two-dimensional modeling of the tracer problem is reviewed.Three-dimensional motions of individual air parcels affected by a planetary wave are investigated theoretically, treating a steady, upward propagating wave in a uniform flow. It is shown that trajectories of air parcels are of elliptical form when projected onto the meridional plane and that they have no mean meridional or vertical motion, even though the usual zonal Eulerian-mean vertical motion exists. The origin of the difference between the mean air parcel motion and the Eulerian-mean motion is discussed.On the basis of the knowledge of air parcel motion, two approaches to two-dimensional modeling are considered. The generalized Lagrangian mean motion (quasi-zonal weighted mean taken over a meandering material tube), recently introduced by Andrews and McIntyre, is identical with the mean motion of an air parcel in a steady state. Such a mean meridional circulation may be used for advecting a tracer in the meridional plane in a two-dimensional model. The transport effect is represented solely by the advection and an eddy transport does not appear in this scheme, to a first approximation.The finding that trajectories of air parcels are elliptical necessitates a reexamination of the Reed-German eddy diffusivity currently used in two-dimensional chemical-dynamical models. By applying a mixing length type hypothesis, we derive an eddy diffusivity formula for use in Eulerian-mean calculations, which, in the case of a conservative tracer is dominated by an anti-symmetric tensor. The eddy transport due to this anti-symmetric tensor diffusivity is of advective type (not diffusive) and has the effect of taking the Stoke drift effect into account, when used in the usual Eulerian-mean formulation. 相似文献
6.
Jacob Bortnik Richard M. Thorne Nigel P. Meredith 《Journal of Atmospheric and Solar》2009,71(16):1636-1646
A brief overview is given of the history of plasmaspheric hiss research, particularly in the context of the recent work by Bortnik et al. (2008) indicating that chorus could be the likely source of plasmaspheric hiss. Previous suggestions given in the literature for this theory are reviewed and then the mechanism itself is outlined, focusing on the characteristic cyclical trajectories executed by typical ray paths that enter into the plasmasphere. A number of directional propagation studies performed in the past are then discussed as well as other work which bears relevance to the present mechanism. 相似文献
7.
N. P. Danilkin G. A. Zhbankov S. V. Zhuravlev N. G. Kotonaeva 《Geomagnetism and Aeronomy》2014,54(4):468-479
Further development of the method of transionospheric radiosounding of the ionosphere in the range of its plasma frequencies is presented. The trajectories of radiowaves with a reflection from the Earth are newly included in the consideration. A modeling of the transionospheric radiosounding was performed in conditions of an irregular ionosphere including moderate-dimensional irregularities with drawing possible trajectories, as well as the obtainment and analysis of the corresponding transionograms. 相似文献
8.
The responses to tidal and/or wind forces of Lagrangian trajectories and Eulerian residual velocity in the southwestern Yellow Sea are investigated using a high-resolution circulation model. The simulated tidal harmonic constants agree well with observations and existing studies. The numerical experiment reproduces the long-range southeastward Eulerian residual current over the sloping bottom around the Yangtze Bank also shown in previous studies. However, the modeled drifters deployed at the northeastern flank of the Yangtze Bank in the simulation move northeastward, crossing over this strong southeastward Eulerian residual current rather than following it. Additional sensitivity experiments reveal that the influence of the Eulerian tidal residual currents on Lagrangian trajectories is relatively weaker than that of the wind driven currents. This result is consistent with the northeastward movement of ARGOS surface drifters actually released in the southwestern Yellow Sea. Further experiments suggest that the quadratic nature of the bottom friction is the crucial factor, in the southwestern Yellow Sea, for the weaker influence of the Eulerian tidal residual currents on the Lagrangian trajectories. This study demonstrates that the Lagrangian trajectories do not follow the Eulerian residual velocity fields in the shallow coastal regions of the southwestern Yellow Sea. 相似文献
9.
Problems of constructing microaccelerometers with the maximally possible resolution are examined, the principles of their
construction and the state of modern developments are discussed, and the way of substantially improving their principal characteristics
is considered. The wide range of scientific and applied problems solved by the application of highly sensitive microaccelerometers
is investigated. 相似文献
10.
推进监测预报体系建设,提高地震预测预报水平 总被引：2，自引：0，他引：2
阴朝民 《地震地磁观测与研究》2003,24(5):1-6
对监测预报工作的地位和作用进行了深入的阐述，分析总结了监测预报工作取得的进展以及存在的问题，提出了未来监测预报体系建设的指导思想和总体目标。并对进一步加强监测预报体系建设，提高预测预报水平各环节的工作进行了详细的论述。 相似文献
11.
We investigate migration of fluids through the rock in the stress corrosion process. The fluids migrate along the trajectories
of the principal stress field. We study geometry of these trajectories, including singularities, limit cycles, and possible
bifurcations. We describe corresponding configurations of weakened zones in the lithosphere due to the fluid migration. 相似文献
12.
根据海口市房屋现状及施工调查情况,分析了地震时由于施工质量问题造成工程结构抗震能力破坏的主要原因,探讨了如何提高建筑物施工质量及抗震性能问题。 相似文献
13.
This paper surveys approaches to the economic valuation of ecosystems and the determination of their optimal utilisation. The components of the value of ecosystems are defined and methods of measurement are presented. Also discussed is a simple model of the economic use of a dynamic ecological system. Economically optimal trajectories are shown and scenarios are presented in which it is economically optimal to destroy the ecosystem. Particular problems arise if the ecosystem is a common-property resource as is often the case with marine ecosystems. This issue is also addressed. Moreover, the paper presents some extensions of the model that add complexity and uncertainty. 相似文献
14.
The value of a formally defined Anthropocene for geomorphologists is discussed. Human impacts have been diachronistic, multifaceted and episodic, as demonstrated by the record of alluvial deposition in the UK. Rather than boxing time into discrete eras or periods, modern research uses calendar dates and multiple dating techniques to explore co‐trajectories for a range of human impacts. Despite the value of ‘The Anthropocene’ as an informal concept and as a prompt to useful debate, arriving at a single, generally acceptable formal definition is impractical, and has some disadvantages. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
15.
The use of Lagrangian trajectories for the identification of the environmentally safe fairways 总被引：1，自引：0，他引：1
We propose and test a method for the optimisation of marine fairways to minimise the risk to high-value areas, based on statistical analysis of Lagrangian trajectories of current-driven pollution transport. The offshore areas are quantified according to the probability of pollution released in these areas to reach vulnerable regions. The method contains an eddy-resolving circulation model, a scheme for tracking of Lagrangian trajectories, a technique for the calculation of quantities characterising the potential of different sea areas to supply adverse impacts, and routines to construct the optimum fairway. The gain is expressed in terms of the probability of pollution transport to the nearshore and the associated time (particle age). The use of the optimum fairway would decrease the probability of coastal pollution by 40% or increase the average time of reaching the pollution to the coast from 5.3 to about 9 days in the Gulf of Finland, the Baltic Sea. 相似文献
16.
17.
根据超声波三维地震模拟实验的结果,研究了绕射波射线轨迹的问题。对绕射波的运动学特征进行了讨论,并引用极值光程律进行了解释。实验和理论的分折指出,绕射点的位置经常按照一定的规律偏离震源--接收点联线的一侧。 本文还提出了“双曲线叠加法”,从而在实际较复杂的情况下,可以用它迅速地确定绕射点的空间位置及波的旅行时间。 文中提出绕射波的运动学特征,从中可以提供一些有关断层或绕射棱结构的情况。至于绕射波的动力学特征及机制将另文阐述。所获的结果及结论有助于物探资料的解释。 相似文献
18.
水库地震监测是我国地震监测的重要组成部分。文中阐述了红水河梯级水电站水库地震监测台网的建设发展历程,详细介绍了天生桥一级、龙滩、岩滩、大化及大藤峡水库专用地震监测台网的建设和发展,并对比分析了库区蓄水前后的地震活动记录,讨论了水库地震监测台网面临的升级改造及运行管理等问题,建议采用流域化统一管理。 相似文献
19.
Transformation of the Ebro River Delta under the Impact of Intense Human-Induced Reduction of Sediment Runoff 总被引：1，自引：0，他引：1
The regularities of the Ebro River delta formation and the impact of hydraulic construction on the river sediment runoff are discussed. As shown, the drastic reduction of the sediment runoff after the construction of two large reservoirs in the lower river reaches in the 1960s slowed down the delta protrusion and intensified the delta coastline washout. 相似文献
20.
Numerical analysis of dislocations of the face slabs of the Zipingpu Concrete Faced Rockfill Dam during the Wenchuan earthquake 总被引：1，自引：1，他引：0
The Zipingpu Concrete Faced Rockfill Dam (CFRD) was obviously damaged during the Wenchuan earthquake in 2008. A wide range of dislocations occurred along the horizontal construction joints at EL. 845m, between the face slabs constructed in the second and third stages. The maximum displacement of the dislocations reached 17cm. In this study, the slab dislocations were investigated using finite element (FE) analysis. The method based on strain potential was applied to compute the permanent deformation of the Zipingpu Dam during the Wenchuan earthquake. The calculated magnitude of the slab dislocation showed good agreements with the field measurements. The dislocation mechanism was discussed. The results show that the dislocation of the concrete slab is a subsequent damage after the permanent deformation of the rockfill materials. The effects of the shear strength and the direction of the construction joints, the reservoir water level and the seismic waves were studied. The shear strength and the direction of the construction joints, reservoir water level and have a significant effect on the dislocation displacement. The dislocation can be effectively reduced by measures such as changing the direction of the construction joints or improving the shear strength at the horizontal joints. 相似文献