Generation of overtides and compound tides in Amazon estuary     

Marcos Nicolás Gallo  Susana Beatriz Vinzon 《Ocean Dynamics》2005,55(5-6):441-448

Tidal propagation in estuaries is affected by friction and fresh water discharge, besides changes in the depth and morphology of the channel. Main distortions imply variations in the mean water level and asymmetry. Tidal asymmetry can be important as a mechanism for sediment accumulation and turbidity maximum formation in estuaries, while mean water level changes can affect navigation depths. Data from several gauges stations from the Amazon estuary and the adjacent coast were analyzed and a 2DH hydrodynamic model was configured in a domain covering the continental shelf up to the last section of the river where the tidal signature is observed. Based on data, theoretical and numerical results, the various influences in the generation of estuarine harmonics are presented, including that of fresh water discharge. It is shown that the main overtide, M₄, derived from the most important astronomic component in the Amazon estuary, M₂, is responsible for the tidal wave asymmetry. This harmonic has its maximum amplitude at the mouth, where minimum depths are found, and then decreases while tide propagates inside the estuary. Also, the numerical results show that the discharge does not affect water level asymmetry; however, the Amazon river discharge plays an important role in the behavior of the horizontal tide. The main compound tide in Amazon estuary, Msf, generated from the combination of the M₂ and S₂, can be strong enough to provoke neap low waters lower than spring ones. The results show this component increasing while going upstream in the estuary, reaching a maximum and then slightly decaying.  相似文献   

Glacier Distribution in the Alps: Statistical Modelling of Altitude and Aspect     

Ian S. Evans 《Geografiska Annaler: Series A, Physical Geography》2006,88(2):115-133

Mass balance of glaciers in mountain areas varies not only with altitude and regional position but also with aspect, gradient, glacier size, glacier type and detailed topographic position. These factors are combined here in models of how glacier altitude varies, tested with data for the Alps edited from the World Glacier Inventory. An overall northward tendency in glacier numbers (toward 005 ± 4°) and lower altitudes (013 ± 5°) is maintained across a range of glacier sizes, types, altitudes and the major divisions of the Alps. Variation with aspect of glacier altitude (and, by implication, of glacier balance) in the Alps is essentially unimodal, and north‐facing glaciers average 220 m lower in middle altitude than south‐facing: 148 m in the Western Alps, 232 m in the West‐central, 252 m in the East‐central, and 268 m in the Eastern Alps. For smaller subdivisions, confidence intervals on estimates are broader and many differences lack statistical significance. Contrasts are greater in the higher massifs, with greater relief, and lower in cloudy, windward areas. There are small windrelated tendencies east of north along the northern and western fringes, but trends across space are weak: position is thus treated by subdivision into districts and groups. Mid‐altitude averages 2891 m overall and varies from 2552 to 3127 m for 27 glacier districts, and from 2124 to 3209 m for 103 glacier groups. Glacier mid‐altitude varies also with glacier form, nourishment, height range and area, which account for over two‐thirds of variance in combined models.  相似文献   

The North-South Asymmetry in the Green Corona     

Elena Dzifčáková  Vojtech Rušin 《Studia Geophysica et Geodaetica》1998,42(2):101-111

The north-south asymmetry of the Fe XIV 530.3 nm coronal emission line (the green corona) over cycle 22 was investigated. The green corona line brightness was dominant in the southern hemisphere during cycle 22 (A = –0.07), except for short periods of the ascending phase of the activity cycle. The asymmetry of the semi-annual mean over the period 1940 – 1996 was also studied. The asymmetry, during these years, reached its maximum in 1962 – 1966, and then decreased. Important periodicities of the asymmetry in cycle 22, e.g., 158 and 350 days, 2.39 years were found. Similar periodicities were also detected in the years 1940 – 1996. An FFT analysis was used to detect these periodicities.  相似文献   

盾构隧道衬砌结构受力分析的梁—弹簧系统模型   总被引：44，自引：6，他引：38  

朱合华  陶履彬 《岩土力学》1998,19(2):26-32

盾构隧道衬砌结构由若干管片及其间的连接螺栓组成。在其断面受力的工程设计中,目前普遍采用梁-弹簧系统模型来模拟其受力性态。其中,梁可分成直梁和曲梁两类。本文在考虑弹簧刚度的轴向、切向和转动效应的同时,从卡氏（Castigliano）第二定理出发,给出了梁-弹簧模型的矩阵式,并论证了直梁-弹簧模型与曲梁-弹簧模型的一致性关系。在数值模拟计算过程中,还考虑了地层反作用力非线性情形和管片接头转动刚度正、负弯矩时的非对称性问题。  相似文献   

Tidal flow asymmetry in the diurnal regime: bed-load transport and morphologic changes around the Red River Delta     

D. S. van Maren  P. Hoekstra  A. J. F. Hoitink 《Ocean Dynamics》2004,54(3-4):424-434

The relation between tidal flow asymmetry and net transport of sediment in the semidiurnal regime has been extensively described. This study reveals that in the diurnal regime, the direction of long-term net bed-load transport and resulting morphologic changes is partly determined by the phase-angle relationship of O₁, K₁, and M₂. Simple analytical formulations of time-averaged bed-load transport were derived which separate the relative contributions of tidal asymmetry from that of residual flow with tidal stirring. In this particular case, the Red River Delta in Vietnam, transports related to tidal asymmetry are larger than those induced by the monsoon currents, and are an order of magnitude larger than those associated with topographic residual flow around the delta. Tide-induced morphologic changes dominate at water depths between 10 and 25 m, of which the patterns of erosion and deposition overlap with observed bathymetric changes. Additional observed changes that occur in more shallow water cannot be explained by tidal asymmetry and are probably related to wave action and to deposition from the buoyant river plume.Responsible Editor: Jens Kappenberg  相似文献   

Climate negotiations beyond Kyoto: developing countries concerns and interests     

Adil Najam  Saleemul Huq  Youba Sokona 《Climate Policy》2003,3(3):221-231

Five years down the road from Kyoto, the Protocol that bears that city’s name still awaits enough qualifying ratifications to come into force. While attention has been understandably focussed on the ratification process, it is time to begin thinking about the next steps for the global climate regime, particularly in terms of a deeper inclusion of developing countries’ concerns and interests. This paper begins doing so from the perspective of the developing countries. The principal argument is that we need to return to the basic principles outlined in the Framework Convention on Climate Change in searching for a north-south bargain on climate change. Such a bargain may be achievable if we can realign the policy architecture of the climate regime to its original stated goals of sustainable development.  相似文献   

Competition and Knowledge in Javanese Rural Business     

Stein Kristiansen 《Singapore journal of tropical geography》2002,23(1):52-69

The paper focuses on information flows and the need for change in cottage industries in rural Indonesia. The context for small-scale business entrepreneurs has changed dramatically during the last decade of economic liberalisation and crisis. Emerging market opportunities, as well as national and international competition, now challenge indigenous businesses in their different geographical settings, and new information is indispensable for survival and growth. The principal question in the paper is whether small-scale agribusiness entrepreneurs are able to identify and utilise existing knowledge for the purpose of improving their competitive strength. By using case studies taking an actor's perspective, the empirical data give insight into the small entrepreneurs' perceptions of their business environments and the hindrances to innovation. Theories on dual economies, path dependence and information asymmetry form the basis for analysing two cases of Javanese agribusiness. The paper concludes that a gap prevails between "traditional" and "modern" sectors of this society, and that cottage industries have much to gain from linking up with external agencies. Regional universities may play a crucial role in enhancing information flows and disseminating competence.  相似文献   

潮汐汊道形态动力过程研究综述   总被引：5，自引：0，他引：5  

高抒 《地球科学进展》2008,23(12):1237-1248

潮汐汊道是潮流作用占优势的沉积环境之一。潮汐汊道系统的口门水道往往是天然航道,在海港建设上具有重要性。从动力地貌学的观点来看,口门水道形态特征和演化研究涉及多种关键的海岸动力过程,因而具有重要的理论意义。均衡态下的潮汐汊道的口门过水断面面积与纳潮量之间存在着幂函数关系,当用传统的O′Brien方法来确定幂函数曲线时,指数n的值变化范围较大,这是由于参与统计分析的部分汊道系统未达到均衡态而造成的;而应用沉积动力学方法,所获的n值稳定在1.15左右,能更好地代表均衡态断面面积。在断面形状上,小型潮汐汊道可以形成宽浅水道中镶嵌次级水道的形态,以适应沉积物输运和堆积过程,提高汊道系统的稳定性。因此,小型潮汐汊道具有不同于大型潮汐汊道的时间—流速不对称特征。这些研究结果在小型汊道的开发和整治工程上具有应用价值。由于口门断面形态是与口门水道和潮流三角洲的整体特征及其动态相联系的,因此,今后的研究重点应是水动力条件、沉积物输运和堆积过程、水道形态之间的反馈关系,以及与纳潮海湾充填同步的潮流三角洲的生长过程,从而使水道地貌演化能够被定量地模拟。  相似文献   

不对称性相互依赖背景下中吉自由贸易实现路径——基于局部均衡理论的模拟          下载免费PDF全文

高志刚  宋亚东 《干旱区地理》2018,41(4):679-685

不对称性相互依赖是中国和吉尔吉斯斯坦经贸合作的常态,中吉自由贸易是丝绸之路经济带互联互通战略的重要组成部分,也是我国向西开展自贸区进程的突破点。文章运用局部均衡模型从BEC产品层面模拟分析了不同关税策略下中吉自贸区的贸易效应及本国经济效应。研究表明：在相同的关税削减幅度的情形下,2002-2016年间中吉贸易效应与其贸易额呈正相关;关税削减对中国和吉尔吉斯斯坦的贸易效应、福利效应及关税损失比较显著,尤其是中国,且对不同商品的影响存在显著差异,其中尤以工业品最为显著;综合考量贸易效应和福利效应,中国的最优策略是直接采取零关税,而吉国则是逐渐削减关税。  相似文献   

On the stability relationships between tidal asymmetry and morphologies of tidal basins and estuaries          下载免费PDF全文

Zeng Zhou  Giovanni Coco  Ian Townend  Zheng Gong  Zhengbing Wang  Changkuan Zhang 《地球表面变化过程与地形》2018,43(9):1943-1959

Simple stability relationships are practically useful to provide a rapid assessment of coastal and estuarine landforms in response to human interventions and long‐term climate change. In this contribution, we review a variety of simple stability relationships which are based on the analysis of tidal asymmetry (TA). Most of the existing TA‐based stability relationships are derived using the one‐dimensional tidal flow equations assuming a certain regular shape of the tidal channel cross‐sections. To facilitate analytical solutions, specific assumptions inevitably need to be made, for example by linearizing the friction term and dropping some negligible terms in the tidal flow equations. We find that three major types of TA‐based stability relationships have been proposed between three non‐dimensional channel geometric ratios (represented by the ratio of channel widths, ratio of wet surface areas and ratio of storage volumes) and the tide‐related parameter a/h (i.e. the ratio between tidal amplitude and mean water depth). Based on established geometric relations, we use these non‐dimensional ratios to restate the existing relationships so that they are directly comparable. Available datasets are further extended to examine the utility of these TA‐based relationships. Although a certain agreement is shown for these relationships, we also observe a large scatter of data points which are collected in different types of landscape, hydrodynamic and sedimentological settings over the world. We discuss in detail the potential reasons for this large scatter and subsequently elaborate on the limited applicability of the various TA‐based stability relationships for practical use. We highlight the need to delve further into what constitutes equilibrium and what is needed to develop more robust measures to determine the morphological state of these systems. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献