Scalar fluxes from urban street canyons. Part I: Laboratory simulation   总被引：3，自引：3，他引：0  

Janet?F.?BarlowEmail author  Ian?N.?Harman  Stephen?E.?Belcher 《Boundary-Layer Meteorology》2004,113(3):369-385

Flow over urban surfaces depends on surface morphology and interaction with the boundary layer above. However, the effect of the flow on scalar fluxes is hard to quantify. The naphthalene sublimation technique was used to quantify scalar vertical fluxes out of a street canyon under neutral conditions. For an array of eight canyons with aspect ratio H/W=0.75 (here, H is building height and W is the street width), increased flux was observed in the first two or three canyons for moderate and low roughness upstream. This is consistent with predictions of the length scale for initial adjustment of flow to an urban canopy. The flux was constant after the initial adjustment region and thus dependent only on local geometry. For a street canyon in the equilibrium part of the array, each facet of the street canyon was coated with naphthalene to simulate scalar release from street, walls and roof, to evaluate the effect of street canyon geometry on fluxes for H/W=0.25, 0.6, 1 and 2. Fluxes from the roof and downstream wall were considerably larger than fluxes from the street and upstream wall, and only the flux from the downstream wall exhibited a simple decrease with H/W. For each H/W there was a monotonic decrease between downstream wall, street and upstream wall transfer. This suggests that flow decelerates around the recirculation region in the lee of the upstream building, i.e. a recirculating jet rather than a symmetrical vortex. The addition of a second source within the street canyon resulted in reduced fluxes from each facet for H/W>0.25, due to increased concentration of naphthalene in the canyon air.  相似文献   

Trawl-induced bottom disturbances off the south coast of Portugal: direct observations by the 'Delta' manned-submersible on the Submarine Canyon of Portimão     

Paulo Morais  Teresa C. Borges  Vera Carnall  Pedro Terrinha  Christopher Cooper  & Richard Cooper 《Marine Ecology》2007,28(S1):112-122

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Shelf-slope exchanges by frontal variability in a steep submarine canyon     

A. Jordi  A. Orfila  G. Basterretxea  J. Tintor 《Progress in Oceanography》2005,66(2-4):120

We study the dynamics of a frontal jet and its short-timescale variability generated by the interaction with a submarine canyon using a limited-area fine-resolution three-dimensional coastal ocean model. The focus is on the steep and narrow Palamós Canyon located off the northeast Catalan coast (northwestern Mediterranean) that is characterized by the presence of a permanent along-slope density-driven current. First, we analyse the stationary circulation induced with different jet locations and show a deflection of the flow in the vicinity of the canyon. Significant vertical motions develop as a result of these current adjustments; the general pattern such as downwelling upstream of the canyon and upwelling downstream are always observed. Second, we analyse the circulation and exchanges associated with an onshore displacement of the jet; thus produces a meander propagating with the flow that interacts with the canyon. We find that the resulting three-dimensional patterns present an oscillation characterized by an intense downwelling followed by upwelling. As a result of this interaction, shelf-slope exchanges and vertical motions are enhanced in the area compared with the passing of a meander above a shelf that is not indented by a submarine canyon. The resulting horizontal transports through the Palamós canyon represent up to 10% of the along-shore fluxes on the shelf and appear to be sufficient to exchange the shelf water of the Gulf of Lions and Catalan sea in 2.5 years. Considering the number of canyons existing in the area, we can estimate an exchange of all the shelf waters in less than 3 months.  相似文献   

南极中山站附近海域水深地形特征   总被引：5，自引：1，他引：4       下载免费PDF全文

冯守珍 《极地研究》2004,16(1):75-80

南极普里兹湾是我国南极中山站建站的重要依托海域 ,是科考船前往中山站进出的必由之路。本文根据普里兹湾近岸的中山站附近海域概略水深 ,研究分析了地形基本概况 ,崎岖不平的中山站近海湾部水下地形 ,沿其湾顶部轴线SN向形成了一条绵延弯曲的水深达 80 0m以浅的海底峡谷 ,通往冰盖底部。峡谷两侧地形复杂 ,水下丘岭嶙峋。从冰盖沿峡谷崩裂下来的冰山 ,最终依其适宜的水深 ,绕过地形障碍 ,沿海底峡谷西侧随风和流往西离去。除中山锚地抛锚区域属于浅水低洼的平缓台地外 ,湾内其它水域可供科考船抛锚的优越水下地形极少  相似文献   

Migration of the lower North Palawan submarine canyon: characteristics and controls     

Shaoru Yin  Weiwei Ding  Weifeng Ding  Yuanyuan Wang 《International Geology Review》2020,62(7-8):988-1005

ABSTRACT

The North Palawan Canyon is a large, previously undescribed submarine canyon that incises the continental shelf and slope of the southern South China Sea. Using multibeam bathymetric data and two-dimensional seismic reflection data, we have characterized current canyon morphology and documented lower-canyon migration in cross-section since the middle Miocene. We have also explored possible causes for the ancient migrations. The 175 km modern canyon is flanked by sediment waves outside its northern bank, and depositional lobes fan out from the canyon mouth. Over the past 15 million years, at least 20 cycles of significant canyon incising and infilling have occurred, along with significant canyon migration. This migration, as recorded in the sedimentary (seismic) record near a leftward bend in the canyon’s lower reach, can be divided into three stages: southward migration during the middle Miocene (averaging 1.24 km/m.y.), northward migration during the late Miocene (1.34 km/m.y.), and stationarity since the Pliocene. The overall zigzagging pattern of the canyon thalweg (as seen in cross-section through time) results from lateral and downstream migration in an aggradational environment. The early (middle to late Miocene) rapid zigzagging migration of the lower main channel, first southward and then northward, was probably associated with the strong collision of the North Palawan Block with the Philippine Mobile Belt, which would have triggered submarine instabilities and deformed the seafloor. The more recent (Pliocene and later) slowing or cessation of canyon migration is likely the result of the now quieter tectonic setting and long-term climatic cooling and drying.  相似文献   

新沭河特大桥工程35m箱梁架桥机架设边梁施工验算     

胡银宝  赖国鳞 《海岸工程》2000,19(2):69-72

新沭河大桥35m预制箱梁在江苏省是首次使用,较以往跨径仅20m的箱梁对架桥机的材料和性能要求高。本文对BBG150型架桥机架设边粱进行了详细验算,为边梁安全架设提供了理论依据。  相似文献   

Diffraction of plane P waves by a canyon of arbitrary shape in poroelastic half-space (Ⅰ): Formulation          下载免费PDF全文

Jianwen Liang  Zhongxian Liu 《地震科学（英文版）》2009,22(3):215-222

This paper presents an indirect boundary integration equation method for diffraction of plane P waves by a two-dimensional canyon of arbitrary shape in poroelastic half-space. The Green's functions of compressional and shear wave sources in poroelastic half-space are derived based on Biot's theory. The scattered waves are constructed using the fictitious wave sources close to the boundary of the canyon, and magnitude of the fictitious wave sources are determined by the boundary conditions. The precision of the method is verified by the satisfaction extent of boundary conditions, the comparison between the degenerated solutions of single-phased half-space and the well-known solutions, and the numerical stability of the method.  相似文献   

固体地球科学研究的重大科学问题     

刘羽 《地球科学进展》2006,21(6):656-657

应美国能源部、美国国家科学基金会、美国地质调查局和美国宇航局的要求,美国国家科学委员会组织专家,研讨驱动固体地球科学研究的重大科学问题。这些问题的研究将深刻影响我们对地球的理解。  相似文献   

SH波入射时半圆形凸起与凹陷地形的地震动   总被引：2，自引：0，他引：2  

吕晓棠  刘殿魁 《地震工程与工程振动》2006,26(5):14-20

研究了弹性半空间中半圆形凸起与凹陷相连地形对SH波的散射问题。将整个求解区域分割为2部分,在其中分别构造满足边界条件的位移解,通过移动坐标使之满足“公共边界”以及半圆形凹陷表面上的边界条件,从而建立起求解该问题的无穷代数方程组。最后,给出了地表位移幅值的数值结果以及凸起地形顶点和凹陷地形最低点处位移幅值的反应谱并进行了讨论。  相似文献   

冲绳海槽西南部新发现"通道-天然堤"系统的成因   总被引：3，自引：0，他引：3  

李军 《海洋地质前沿》2004,20(2):5-7

Sibuet等(1998)首次发现了冲绳海槽西南部发育有两条大型的海底“通道一天然堤”沉积系统。这一大型海底冲积扇典型组成单元的发现为冲绳海槽南部以海底峡谷为主要渠道的陆源物质输运作用和浊流沉积作用提供了直接证据。结合地球物理调查资料,同时对比其他典型区域的特征,对其成因和形成时代进行了初步探讨。  相似文献