Numerical Study on the Impact of Ground Heating and Ambient Wind Speed on Flow Fields in Street Canyons     

LI Lei  YANG Lin  ZHANG Li-Jie  JIANG Yin 《大气科学进展》2012,29(6):1227-1237

The impact of ground heating on flow fields in street canyons under different ambient wind speed conditions was studied based on numerical methods.A series of numerical tests were performed,and three factors including height-to-width(H/W) ratio,ambient wind speed and ground heating intensity were taken into account.Three types of street canyon with H/W ratios of 0.5,1.0 and 2.0,respectively,were used in the simulation and seven speed values ranging from 0.0 to 3.0 m s 1 were set for the ambient wind speed.The ground heating intensity,which was defined as the difference between the ground temperature and air temperature,ranged from 10 to 40 K with an increase of 10 K in the tests.The results showed that under calm conditions,ground heating could induce circulation with a wind speed of around 1.0 m s 1,which is enough to disperse pollutants in a street canyon.It was also found that an ambient wind speed threshold may exist for street canyons with a fixed H/W ratio.When ambient wind speed was lower than the threshold identified in this study,the impact of the thermal effect on the flow field was obvious,and there existed a multi-vortex flow pattern in the street canyon.When the ambient wind speed was higher than the threshold,the circulation pattern was basically determined by dynamic effects.The tests on the impact of heating intensity showed that a higher ground heating intensity could strengthen the vortical flow within the street canyon,which would help improve pollutant diffusion capability in street canyons.  相似文献   

Influence of an oxygen minimum zone and macroalgal enrichment on benthic megafaunal community composition in a NE Pacific submarine canyon          下载免费PDF全文

Lia Domke  Myriam Lacharité  Anna Metaxas  Marjolaine Matabos 《Marine Ecology》2017,38(6)

Megafaunal diversity in the deep sea shows a parabolic pattern with depth. It can be affected by factors such as low oxygen concentration, which suppresses diversity, or the presence of submarine canyons, which enhances it. Barkley Canyon, located off the west coast of British Columbia, Canada, is a submarine canyon that extends from the continental margin (200 m) into the deep ocean (2,000 m). This canyon receives drift kelp from shoreline kelp forests and contains an oxygen minimum zone (OMZ) at 500 to 1,500 m depth. Our study investigated the abundance and diversity of epibenthic megafauna over a range of depths (200–2,000 m) and oxygen concentrations (0.5–5.0 ml/L) within Barkley Canyon, as well as changes in abundance near detrital kelp. Video was collected using the remotely operated vehicle ROPOS along seven 1‐km cross‐canyon (i.e., across the axis of the canyon) transects and three 40‐m perpendicular cross‐transects over kelp. Taxonomic groups were associated with depth, temperature, and the presence of pebbles. The OMZ restricted pennatulids, and edge effects along OMZ boundaries were observed for ophiuroids. The geomorphology of the sea floor affected the distribution of taxa across the canyon, with Porifera mainly found along the walls and Echinoidea within the canyon axis. Expected richness exhibited a bimodal pattern, peaking at 300 and 2,000 m, possibly due to the combined effect of the OMZ and the submarine canyon. Echinoidea aggregated near drift kelp at 200 and 300 m. We found that faunal communities in Barkley Canyon were influenced by several confounded factors including depth, oxygen and substrate. Understanding faunal patterns is paramount with increased exploitation and a changing climate.  相似文献   

塔里木盆地塔河油田岩溶峡谷区海西早期洞穴系统发育模式^*          下载免费PDF全文

李源  鲁新便  蔡忠贤  张恒  刘显凤 《古地理学报》2017,19(2):364-372

塔河油田岩溶峡谷区发育大型岩溶洞穴型储集层,勘探效果较好。基于三维地震资料、钻井资料,并结合地震属性提取技术,对地下岩溶洞穴系统、古地貌、古水文系统进行精细刻画,探讨洞穴形成机理,进而总结洞穴发育模式。研究结果表明: (1)峡谷上游段地表水垂向侵蚀作用强烈,峡谷失去了排水功能演变为干谷,下游段水动力条件减弱。(2)峡谷区岩溶洞穴类型划分为暗河洞穴、峡谷—断裂双控型洞穴。暗河洞穴主要发育在峡谷上游段,与峡谷呈“映射”关系。峡谷—断裂双控洞穴发育于峡谷两侧,垂向上具有多层性特征。(3)综上探讨峡谷区岩溶洞穴形成机理,认为较充足的水源补给条件以及水流强烈的垂向侵蚀溶蚀作用控制了暗河洞穴发育,多期次排泄基面下降以及断裂系统共同控制峡谷—断裂双控洞穴的发育。结合现代恩施地区洞穴系统特征,提出了峡谷地区洞穴发育模式,为下一步洞穴储集层预测和勘探实践提供理论借鉴。  相似文献   

2.5D scattering of incident plane SH waves by a canyon in layered half-space     

Zhenning Ba  Jianwen Liang 《地震学报(英文版)》2010,(1):25-33

This paper presents 2.5D scattering of incident plane SH waves by a canyon in layered half-space by the indirect boundary element method (IBEM). The free field response is carried out to give the displacements and stresses on the line which forms boundary of the canyon. The fictitious uniform moving loads are applied to the same line to calculate the Green’s functions for the displacements and stresses. The amplitudes of the loads are determined by the boundary conditions. The displacements due to the free ...  相似文献   

未来气候变化科学研究的主要方向和挑战     

孙颖  秦大河  周波涛 《气候变化研究进展》2015,11(5):324-330

2014年9月,IPCC联合世界气候研究计划（WCRP）,在瑞士伯尔尼大学召开了一次特别的研讨会,总结过去几年气候变化科学研究中所取得的经验教训。此次会议针对IPCC最新评估报告中的关键不确定性,梳理并总结了未来气候变化研究的主要科学方向和面临的主要挑战,讨论了如何与WCRP计划结合并解决这些问题,以期在未来更好地应对这些挑战。在此次会议上,与会专家提出,未来气候变化科学研究的重大挑战应包括如下8个主题。云、环流与气候敏感度;理解和预测极端天气气候事件;冰冻圈变化;区域气候信息;区域海平面上升及其对沿海地区的影响;水资源可利用量;生物地球化学、气溶胶和大气化学;理解年代际变化：归因与预测。这些主题涵盖了WCRP计划的六大挑战和其他被认为具有挑战性的主题。本文将在此次会议报告的基础上,对相关内容进行介绍,以供当前的气候变化工作参考。  相似文献   

四川八台山绝壁峡谷地质遗迹特色及保护策略   总被引：1，自引：0，他引：1  

张会明  万新南  陈利娟  张玲 《四川地质学报》2009,29(1):84-86

位于川、陕、渝交界的八台山省级地质公园,发育着独特的绝壁峡谷地貌,地质遗迹资源丰富,具有重要的旅游和科研价值。文章初步论述了绝壁峡谷地貌发育的区域地质背景、地貌景观特色,提出了对景区地质遗迹景观的保护策略。  相似文献   

城市街道峡谷对称性对内部气流场的影响研究   总被引：4，自引：1，他引：3       下载免费PDF全文

何泽能  高阳华  李永华  李振山 《气象与环境学报》2008,24(2):62-67

应用雷诺应力湍流模型,模拟了不同高度比的城市街道峡谷的气流场。结果表明:峡谷的对称性对其内部气流场有显著影响。前高后低型峡谷下部为逆时针旋涡,上部为顺时针旋涡,峡谷越深,流场发展的越充分;峡谷内部墙面存在明显的驻点。前低后高型峡谷只存在一个大的顺时针旋涡,随着峡谷的加深,内部气流速率有减小的趋势;峡谷达到一定深度后出现驻点。对称型峡谷内部形成了顺时针旋涡,强度不大;随着峡谷的加深,内部流场转为一顺一反2个旋涡的二元结构;仅当峡谷很深时才出现明显驻点。前低后高型峡谷的气流场形式更有利于污染物的迁移、扩散,在城市规划中应尽量结合主导风向设计这类建筑布局。  相似文献   

Near-inertial motions in and around the Palamós submarine canyon (NW Mediterranean) generated by a severe storm     

Antoni Jordi  Dong-Ping Wang 《Continental Shelf Research》2008,28(17):150-2534

During 9–16 November 2001 the western Mediterranean Sea was lashed by one of the most extreme storms of the last decades. Current meter data from seven moorings in the Palamós submarine canyon (northwestern Mediterranean) are analyzed to understand the vertical propagation of near-inertial energy generated by the storm. The daily inertial rotary components are examined for evidence of free and forced near-inertial oscillations. Free near-inertial motions are increased during the storm, although they are larger outside the canyon than inside. Conversely, forced near-inertial motions are relatively large inside the canyon but are almost negligible outside. Based on the results of a three-dimensional ocean circulation model, these differences are shown to be caused by the presence of a storm-generated alongshore front. The mechanisms by which near-inertial energy propagates are distinct at each side of the front. On the onshore side of the front (inside the canyon), free near-inertial motions are rapidly carried away by normal inertial waves, and wave reflection off canyon wall is responsible for the dissipation of free near-inertial motions and enhancement of forced near-inertial motions. On the offshore side of the front (outside the canyon), on the other hand, free near-inertial motions propagates first downward with anomalously low frequency internal waves and are then advected southward and offshore by the mean flow.  相似文献   

Dense shelf water cascades and sedimentary furrow formation in the Cap de Creus Canyon,northwestern Mediterranean Sea   总被引：1，自引：0，他引：1  

P. Puig  A. Palanques  D.L. Orange  G. Lastras  M. Canals 《Continental Shelf Research》2008

To investigate the processes by which sediment is transported through a submarine canyon incised in a continental margin affected by recurrent dense shelf water cascading events, several instrumented moorings were deployed in the Cap de Creus Canyon from September 2004 to September 2005. This was done as part of the EuroSTRATAFORM Program that investigated sediment transport and accumulation processes in the Gulf of Lions. Results obtained in this observational study confirm that major cascading events can effectively contribute to the rapid export of sediment from the shelf and upper slope to deeper environments, and suggest that the associated strong currents carrying coarse particles are able to erode the canyon floor and generate sedimentary furrows. During winter 2004–2005, persistent northerly winds and the absence of river floods contributed to decrease the buoyancy of coastal waters and to dramatically enhance the intensity of dense shelf water cascades in the Gulf of Lions. Under such conditions, cascading continuously affected the entire Cap de Creus upper canyon section for more than a month and sustained cold temperatures and down-canyon steady currents >60 cm/s (up to 100 cm/s), showing periodic fluctuations that lasted between 3 and 6 days. Increases in suspended sediment concentrations were associated with dense shelf water cascading outbursts, but the magnitude of the concentration peaks decreased with time, suggesting a progressive exhaustion of the resuspendable sediments from the shelf and canyon floor. Grain size analyses of the particles caught by a near-bottom sediment trap show that dense shelf water cascades are able to transport coarse sediments (up to 65% sand) in suspension (and presumably as bed load), which have the potential to abrade the seafloor and generate erosive bed forms. The orientation of a large field of “wide” (i.e., widths about 1/2 spacing indicative of erosive formation) sedimentary furrows recently observed in the Cap de Creus Canyon clearly coincides with the preferential direction of highest velocities measured by the moored current meters, indicating a causative relationship between contemporary dense shelf water cascades and furrow formation.  相似文献   

徒步穿越考察世界第一大峡谷最新成果   总被引：4，自引：0，他引：4  

杨逸畴 《山地学报》1999,17(3)

介绍了人类首次徒步穿越和科学考察雅鲁藏布大峡谷的最新成果。  相似文献