A Parameterization of Third-order Moments for the Dry Convective Boundary Layer     

Séverine Tomas  Valéry Masson 《Boundary-Layer Meteorology》2006,120(3):437-454

We describe one-dimensional (1D) simulations of the countergradient zone of mean potential temperature observed in the convective boundary layer (CBL). The method takes into account the third-order moments (TOMs) in a turbulent scheme of relatively low order, using the turbulent kinetic energy equation but without prognostic equations for other second-order moments. The countergradient term is formally linked to the third-order moments and , and a simple parameterization of these TOMs is proposed. It is validated for several cases of a dry CBL, using large-eddy simulations that have been realized from the MESO-NH model. The analysis of the simulations shows that TOMs are responsible for the inversion of the sign of in the higher part of the CBL, and budget analysis shows that the main terms responsible for turbulent fluxes and variances are now well reproduced.  相似文献   

Instabilities of the tidally induced bottom boundary layer in the rotating frame and their mixing effect     

K. Sakamoto  K. Akitomo 《Dynamics of Atmospheres and Oceans》2006,41(3-4):191-211

To investigate the stability of the bottom boundary layer induced by tidal flow (oscillating flow) in a rotating frame, numerical experiments have been carried out with a two-dimensional non-hydrostatic model. Under homogeneous conditions three types of instability are found depending on the temporal Rossby number Ro_t, the ratio of the inertial and tidal periods. When Ro_t < 0.9 (subinertial range), the Ekman type I instability occurs because the effect of rotation is dominant though the flow becomes more stable than the steady Ekman flow with increasing Ro_t. When Ro_t > 1.1 (superinertial range), the Stokes layer instability is excited as in the absence of rotation. When 0.9 < Ro_t < 1.1 (near-inertial range), the Ekman type I or type II instability appears as in the steady Ekman layer. Being much thickened (100 m), the boundary layer becomes unstable even if tidal flow is weak (5 cm/s). The large vertical scale enhances the contribution of the Coriolis effect to destabilization, so that the type II instability tends to appear when Ro_t > 1.0. However, when Ro_t < 1.0, the type I instability rather than the type II instability appears because the downward phase change of tidal flow acts to suppress the latter. To evaluate the mixing effect of these instabilities, some experiments have been executed under a weak stratification peculiar to polar oceans (the buoyancy frequency N²  10⁻⁶ s⁻²). Strong mixing occurs in the subinertial and near-inertial ranges such that tracer is well mixed in the boundary layer and an apparent diffusivity there is evaluated at 150–300 cm²/s. This suggests that effective mixing due to these instabilities may play an important role in determining the properties of dense shelf water in the polar regions.  相似文献   

Quantifying the environmental impacts of artisanal fishing gear on Kenya's coral reef ecosystems     

Mangi SC  Roberts CM 《Marine pollution bulletin》2006,52(12):1646-1660

The environmental impacts of artisanal fishing gear on coral reef ecosystems were studied in the multi-gear fishery of southern Kenya to evaluate which types of gear have the greatest impact on coral reef biodiversity. The gear types studied were large and small traps, gill nets, beach seines, hand lines and spear guns. Levels of coral damage, proportion of juvenile fish and discards, size and maturity stage at first capture were quantified and compared amongst the gear types. Results indicate that fishers using beach seines, spears and gill nets cause the most direct physical damage to corals. Spear fishers showed the highest number of contacts to live corals per unit catch followed by fishers using gill nets (12.6 ± 1.8 and 5.9 ± 2.0 coral contacts per kg fish caught per trip respectively). Apart from discarding 6.5% of their daily catch in the sea, as it was too small, beach seine fishers also landed the highest percentage of juvenile fish (68.4 ± 15.7%), a proportion significantly higher (p < 0.001) than in any other gear. The size and maturity stage at first capture for 150 of 195 species caught by all gear types was well below the lengths at which they mature. For example, 100% of Lethrinus xanthochilus, 99% of Lethrinus nebulosus and 94% of Lethrinus harak caught were juveniles. Across all gear types, 50.1 ± 22.7% of the catch consisted of juvenile fish, indicating serious growth overfishing. Field assessment of levels of coral density showed that fishing grounds where beach seines were still in use had a significantly lower density than where beach seining was not used. This correlation is likely to arise in part because seines cannot be used in the most coral rich areas, and in part because coral loss is a consequence of seine use. On a per gear basis therefore, beach seines had the most impact on coral reef biodiversity. This study emphasizes the need to enforce restrictions on destructive gear and mesh sizes.  相似文献   

基于孔压静力触探(CPTU)测试的连云港海相粘土前期固结压力确定方法研究     

蔡国军  刘松玉  童立元  杜广印 《工程地质学报》2007,15(1):83-87

首先回顾了基于孔压静力触探(CPTU)测试确定前期固结压力的方法,通过连云港海相粘土场地进行的CPTU试验资料,以室内固结试验得到的前期固结压力作为参考值评估了经验方法预测前期固结压力的有效性。最简单的方法是直接建立前期固结压力和净锥尖阻力的关系,同时也是最有效的方法。  相似文献   

桐梓北部大竹坝井田含煤地层及可采煤层地质特征     

廖友常 《贵州地质》2007,24(3):202-206

大竹坝井田位于呈北东向展布的松坎复式向斜南东翼之次级褶皱-乐坪背斜南东翼,含煤地层为上二叠统龙潭组(P3l),厚45.61~71.53m,平均厚61.10m,含煤层(线)2~6层,全区可采煤层一层(C3),局部可采煤层二层(C2、C4)。C3煤层具有低挥发份、中灰、中高硫、高固定碳、高熔灰分、高热值的特点。可作工业用煤、动力用煤、气化用煤和化工用煤以及民用等。井田以含煤地层相对较薄,可采煤层少,煤层厚度小,含煤率低为其特征。  相似文献   

中国海相碳酸盐岩的储层类型、勘探领域及勘探战略   总被引：18，自引：3，他引：18  

赵宗举  范国章  吴兴宁  陈子炓 《海相油气地质》2007,12(1):1-11

中国海相碳酸盐岩有效储层成因类型主要包括古风化壳岩溶储层、礁滩储层及层状白云岩储层三大类。陆上中—古生界盆地三类储层均有分布,海上第三系盆地主要发育礁滩储层。针对我国海相油气地质特别是陆上中—古生界油气成藏的复杂性,提出应该加强对勘探及认识程度相对较低的礁滩储层形成的原生岩性-成岩圈闭油气藏的研究与勘探工作。石灰岩古风化壳岩溶储层具有强烈的非均质性,白云岩储层的含油气性比较依赖于有效储盖组合及构造圈闭。鉴于我国海相油气资源潜力巨大、勘探程度较低,故应该加强海相油气资源特别是陆上主要盆地海相油气资源及南海油气资源的研究与勘探开发,尤其要加强层序地层及岩相古地理编图等基础油气地质研究工作。  相似文献   

混沌功率谱熵方法在识别水淹低阻油层中的应用     

江波  王任一  齐红霞 《江苏地质》2007,31(3):232-235

储集层孔隙度和电阻率曲线间微差形态波形的复杂程度隐含着储集层含油气性的信息,可以用混沌动力学系统加以刻划。油层相空间庞加莱截面明显具有自相似结构,呈现混沌特性;而水淹层和水层的相空间庞加莱截面显示,其混沌性呈显著减弱之势,系统趋于简单有序。其功率谱密度不论水淹程度如何,整体为一随频率增大其能量按指数递减连续频谱;随水淹程度逐渐减弱,递减幅度减小,整体能量逐渐降低,某些频率成分被吸收削弱,由光滑状逐渐演变成锯齿起伏状,其功率谱熵逐渐增大。基于测井信息的混沌特征和功率谱熵特征识别水淹层的方法,对利用传统测井解释理论判别比较困难的低阻油层有较强的识别能力。  相似文献   

机载激光雷达对青岛及周边海域的气溶胶探测   总被引：11，自引：1，他引：11       下载免费PDF全文

毛敏娟  张寅超  方海涛  戚福弟  邵石生  胡欢陵  周军 《地球物理学报》2007,50(2):370-376

工作波长为532 nm的机载大气环境探测激光雷达AEDAL（Atmospheric Environment Detecting Airborne Lidar）装载在CMS_3807飞机上，于2005年11月7～11日期间在青岛地区及周边海域上空进行了飞行探测.此次实验的目的有两个：验证我国用于大气环境探测的激光雷达技术已经具备从地基向空基乃至天基发展的条件；获得青岛地区及周边海域边界层结构及大气气溶胶时空分布变化的特点.激光雷达的高时空分辨率为获取飞行路径上的边界层结构及气溶胶时空分布提供了可能.为了研究下垫面对边界层及气溶胶时空分布的影响，预定的飞行路径上包含了丰富的地形变化，有城市、丘陵、海区等.通过给出11月8日及11日的探测结果，不仅得到了不同地区边界层结构及气溶胶的时空分布特点，还可以看到冷锋、地形、地面气象场等因素对它们的影响.  相似文献   

完全匹配层吸收边界在孔隙介质弹性波模拟中的应用   总被引：14，自引：6，他引：14       下载免费PDF全文

赵海波  王秀明  王东  陈浩 《地球物理学报》2007,50(2):581-591

模拟弹性波在孔隙介质中传播，需要稳定有效的吸收边界来消除或尽可能的减小由人工边界引起的虚假反射. 本文在前人工作基础上，首次建立了弹性孔隙介质情况下完全匹配层吸收边界的高阶速度-应力交错网格有限差分算法，并详细讨论了完全匹配层的构建及其有限差分算法实现. 首先，本文通过均匀孔隙模型的数值解与解析解的对比，验证所提出的数值方法的正确性；然后，本文考察了完全匹配层对不同入射角度入射波和自由表面上的瑞利波的吸收性能，将完全匹配层与廖氏和阻尼吸收边界进行了对比，研究了这三种吸收边界在不同吸收厚度情况下对弹性波吸收能力. 数值结果表明，在孔隙介质中，完全匹配层作为吸收边界能十分有效地吸收衰减外行波，无论对体波还是面波，是一种高效边界吸收算法.  相似文献   

潜孔锤跟管钻进技术在小浪底水利观测孔工程的应用     

郑玉辉 《探矿工程》2007,34(8):4-5,12

在黄河小浪底水利枢纽观测孔工程中,采用气动潜孔锤跟管钻进结合双动力头钻机成功地解决了普通气动潜孔锤及常规钻进工艺在厚度达50 m渣石层成孔难的问题。  相似文献