The challenge of modeling pool–riffle morphologies in channels with different densities of large woody debris and boulders     

Douglas M. Thompson 《地球表面变化过程与地形》2012,37(2):223-239

Studies on pool morphologies include reports of over 80% or 90% of pools being associated with structural controls and large obstructions that include boulders, bedrock outcrops and large woody debris (LWD). A Monte Carlo simulation approach and developmental computer model was created to predict pool formation, spacing and the percentage length covered by pools, riffles, scour holes and runs based on input data that include channel slope, width, the number of small and large boulders, and the number of 10–30 cm, 30–60 cm and >60 cm pieces of wood. The statistical‐empirical model is founded on the idea that boulders, bedrock outcrops and large woody debris provide a physical framework that then controls local water‐surface slopes, velocity patterns and the locations of pools and riffles. The spacing values of individual types and sizes of obstructions are modeled as log‐normal distributions with separate distributions for each obstruction type. Pools are assigned different probabilities of development depending on the obstruction type. Pool and riffle lengths used to create the subsequent morphology follow their own slope‐dependent, log‐normal trends. A minimum distance develops between successive pools because of the backwater and turbulent conditions needed for pool formation. The total number and spacing of pools, riffles and scour holes thus reflects the number and locations of obstructions and characteristics of the pool–riffle couplet. The simulation model accurately captures the number of pools in the modeled data range at 65% of all the verification field sites, and 86% of the verification field sites with a more limited range of width and slope characteristics. Lower levels of prediction capabilities are associated with modeled numbers of scour holes and log jams. The model accurately mimics some statistical attributes of pool spacing, and future versions of the model could be developed to improve overall predictive capabilities. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

西太平洋暖池区域热通量变化及其与南海夏季风爆发的关系     

左涛  陈锦年  王宏娜 《海洋学研究》2012,30(2):5-13

利用卫星遥感资料反演出的海洋大气参数,应用目前世界较为先进的通量算法(CORAER 3.0),计算了西太平洋区域海-气热通量(感热通量和潜热通量)。首先分析了海-气热通量的多年平均场和气候场变化的基本特征,以及年际和年代际变化特征;进而对其与南海夏季风爆发之间的关系进行了初步探讨。结果表明,西太平洋海-气热通量具有明显的时空分布特征,感热通量的最大值出现在黑潮区域,潜热通量的最大值出现在北赤道流区和黑潮区域。在气候平均场中,黑潮区域的感热通量和潜热通量最大值均出现在冬季,最小值出现在夏季;暖池区域感热通量除了春季较小外,冬、夏和秋季基本相同,而潜热通量最大值出现在秋、冬季,最小值出现在春、夏季。另外,海-气热通量还具有显著的年际变化和年代际变化,感热通量和潜热通量均存在16 a周期,与南海夏季风爆发存在相同的周期。由相关分析可知,4月份暖池区域的海-气热通量与滞后3 a的南海夏季风爆发之间存在密切相关关系,这种时滞相关性,可以用于进行南海夏季风爆发的预测,为我国汛期降水预报提供科学依据。基于以上结论,建立多元回归方程对2012年的南海夏季风爆发进行了预测,预测2012年南海夏季风爆发将偏晚1～2候左右。  相似文献   

海上溢油油膜厚度浮标结构设计研究     

王晶  王春谊  王项南  王士一 《海洋技术学报》2012,31(1):49-51,122

介绍了海上溢油油膜浮标的采样池和整体结构设计,综合考虑浮标的重量、浮力和压力等因素,分析了浮标在水中的静态特性和结构强度,最终研制了符合结构设计要求的油膜浮标,通过实验证明其可靠性及密封性能良好。  相似文献   

一次切断低压诱发的暖区深对流与异常副热带锋及其平流层-对流层交换   总被引：3，自引：2，他引：1       下载免费PDF全文

施春华  李慧  郑彬  郭栋  刘仁强 《地球物理学报》2014,57(1):21-30

采用Cloudsat/CPR云雷达,FY2C/TBB亮温,Aura/MLS大气成分等卫星遥感资料,结合ECMWF气象分析资料和HYSPLIT4轨迹模式,研究了2009年6月一次东亚切断低压的暖区深对流和异常副热带锋面的结构和演变.分析表明,由于低压切断前的旧槽背景,在低涡的近成熟期,内部冷、暖锋降水偏弱,边沿的高空副热带锋面异常发展到对流层底部,低空西南暖湿水汽在副热带锋前聚集,形成千公里长的暖区深对流降水带.随着该锋面的快速东移,副热带锋区进入原暖区雨带,锋区热力间接次级环流的强上升支,加强了锋下冷侧（原暖湿区）的深对流,但该锋面阻挡了来自暖侧的水汽补充,降水结束.该异常副热带锋区还发生了强烈的平流层-对流层相互交换,在高空急流出口区的下方,平流层1.5PVU等位涡线向下入侵可达5.5 km（约500 hPa）处,锋下向上的深对流注入可达10 km,在入侵-注入混合区,臭氧和水汽的散点图上出现了二者浓度双高和双低的特殊气团.  相似文献   

Linux下一种多核网络服务器模型设计与实现     

杨小宇  杨斌 《成都信息工程学院学报》2010,25(6)

传统的基于Linux操作系统的网络服务器程序在高负载情况下不能充分利用多核服务器硬件资源,其原因主要在于没有找到一种高效的服务器编程解决方案.为了解决这一问题,在分析了线程池技术和linux 2.6内核下的I/O多路复用技术各自的优缺点的基础上,设计并实现了一种在多核服务器平台上结合线程池和I/O多路复用的高性能网络服务器编程模型.通过实验表明,新的编程模型相对于线程池模型和单纯的I/O多路复用模型,其任务平均响应时间只占其它两种模型的8%和29%,而其平均吞吐量则达到了其它两种模型的8.4倍和1.9倍.  相似文献   

沙坡头地区生物土壤结皮-土壤系统生长季氮矿化动态     

虎瑞  王新平  潘颜霞  张亚峰  张浩  陈宁 《中国沙漠》2016,36(1):174-180

以腾格里沙漠东南缘沙坡头天然植被区藻地衣混生结皮和无结皮土壤为对象,采用野外原状土柱封顶埋管法,研究土壤硝态氮、无机氮、净硝化速率和净氮矿化速率的季节动态特征。结果表明:藻地衣混生结皮和无结皮土壤有效氮含量和净氮转化速率存在明显的季节动态,表现为生长季高峰期 > 生长季初期,夏季7月和8月土壤有效氮和净氮转化速率最大;两个样地土壤在生长季不同时期有效氮和净氮转化速率也存在差异。生长季初期,藻地衣混生结皮和无结皮土壤硝态氮和无机氮含量无显著差异,且温度是影响土壤氮素转化的关键环境因子。生长季高峰期,两个样地土壤有效氮含量和净硝化速率均表现为无结皮 > 藻地衣混生结皮,且水分和温度分别是影响土壤氮硝化和矿化过程的关键环境因子。由此可见,藻地衣结皮的繁衍在一定程度上抑制了土壤氮的硝化过程,因而可以减少养分的散失,是养分贮存的重要机制。  相似文献   

酒西坳陷青西凹陷富油的地质-地球化学因素分析   总被引：3，自引：0，他引：3  

杨智明  王琪  史基安  李曼茹  王雷 《沉积学报》2003,21(4):695-700

青西凹陷下白垩统暗色半深湖相-深湖相的泥岩、白云质泥岩和泥质白云岩为研究区主力烃源岩,其沉积时为整体上处于封闭-半封闭强还原-还原环境的断陷湖泊,有利于有机质的保存和转化,且烃源岩厚度占地层比例均大于 5 0%以上,加之有机质类型以混合型为主、有机碳含量普遍大于 1%,为油田形成提供了重要的物质基础。喜山期构造运动形成了许多挤压逆断层、剪切性断层和构造缝,造成地层和构造叠覆,为有机质成熟、运移和聚集提供了动力和空间,从而为该区油藏的形成提供了有利条件.  相似文献   

NUMERICAL STUDY ON THE FORMATION OF THE SOUTH CHINA SEA WARM CURRENT Ⅱ. BAROCLINIC CASE     

王凯方国洪  施心慧 《中国海洋湖沼学报》2001,19(4):306-311

In this part, Levitus‘ climatological temperature and salinity are incorporated in the numerical model developed in Part I. Diagnostic and prognostic experiment on the thermohaline circulation were conducted. The smooth Levitus‘ data do not include any information on the South China Sea Warm Current (SCSWC), so it is not in the model-produced diagnostic thermohaline circulation. Although the SCSWC does not appear in the wind-driven circulation in the barotropic case, it appears in the prognostic wind-driven circulation in the baroclinic case. This implies that the differing circulation pat-terns between barotropic case and bareclinic case are due to the stratification. The prognostic thermohaline circulation with wind stress and inflow/outflow transports at open boundaries are also discussed. Coupling of density and dynamic forces makes the circulation pattern more complicated, Even though the stratification is not always a direct cause of the formation of the SCSWC, it is at least an indirect cause.  相似文献   

NUMERICAL STUDY ON THE FORMATION OF THE SOUTH CHINA SEA WARM CURRENT Ⅰ.BAROTROPIC CASE     

王凯  方越 《中国海洋湖沼学报》2001,19(1):1-9

In this work, Princeton Ocean Model (POM) was used to study the formation of the South China Sea Warm Current (SCSWC) in the barotropic case. Monthly averaged wind stress and the inflow/outflow transports in January were used in the numerical simulation which reproduced the SCSWC. The effects of wind stress and inflow/outflow were studied separately. Numerical experiments showed thatthe Kuroshio intrusion through the Luzon Strait and the slope shelf in the northern SCS are necessary conditions for the founation of the SCSWC. In a flat bottom topography experiment, the wind stress drivennortheast current in the northern SCS is a compensatory current.  相似文献   

西太平洋暖池海温分布型及其与东亚大气环流的关系   总被引：1，自引：0，他引：1  

张增信  刘宣飞  滕代高 《南京气象学院学报》2005,28(6):746-754

采用海温资料和NCEP/NCAR 49 a再分析的高度场、风场资料,利用EOF、合成分析方法,研究了夏季暖池SSTA的时空演变,结果显示:夏季暖池SSTA具有整体一致性分布和南北区域的反对称分布两种空间分布型。根据这两种分布型划分了夏季暖池海温正、负异常年,分析了相应年份的风场环流特征,结果表明:SSTA为一致性分布时,暖异常年850 hPa暖池区上空有一反气旋偏差环流,副热带地区西风和低纬度地区东风都得到加强,200 hPa南亚上空为一反气旋偏差环流,沃克环流得到加强;冷异常年则相反。当SSTA为南北反对称分布时,北暖南冷年850 hPa暖池区上空为一反气旋偏差环流,15°N附近东风气流和赤道附近西风气流增强,200 hPa反气旋偏差环流中心移到东亚大陆上空,长江中下游地区为上升气流,降水明显增多,华北地区为下沉气流,降水减少;冷异常年则相反。  相似文献