The role of wavegroup velocity in the blocking problem     

Martin Dunst 《Pure and Applied Geophysics》1977,115(3):459-471

Considering the blocking problem as a baroclinic instability problem in a dispersive wave system with diabatic heating effects, it is of great interest to investigate the role of wavegroup velocityv _gr in blocking processes, becausev _gr controls the energy transfer in the wave field. Using a Newtonian Cooling —type of forcing with a phase differencek to the main field and taking the linearized version of a two-level model, the phase speedc _r, the group velocityv _gr and the growth ratekc _i have been obtained as analytical functions of the mean zonal windU, the thermal windU _T, the coefficient of diabatic heating x, the phase differencek and the wavelengthL. Now the hypothesis is introduced, that a blocking should be expected, ifv _gr has a maximum value in the vicinity ofL _o, for whichc _r vanishes and thee-folding timet=1/kc _i (kc _i>0) is smaller than 6 days (see condition (20) in the text). One finds, that for special parameter combinations (U _T, U, ), where 15 m/secU _T25m/sec,U=10m/sec, 0.8·10^–51.5·10^–5 [sec^–1], certain valuesL _o with an appropriate phase differencek exist, which satisfy the conditions mentioned above (for values see Table 2). TherebyL _o varies within the range 8500 km <L _o<11000 km corresponding to the preferred planetary blocking wavenumber 2 in middle latitudes 50°<<70° N.  相似文献   

Test of scale modelling of sediment transport in steady unidirectional flow     

John B. Southard  Lawrence A. Boguchwal  Richard D. Romea 《地球表面变化过程与地形》1980,5(1):17-23

In two steady uniform flows at different physical scales in a small open channel, with variables characterizing flow, sediment, and fluid adjusted for dynamic similitude by means of four dimensionless modelling parameters (a Reynolds number, a Froude number, a density ratio, and a length ratio), measured frequency distributions of height, spacing, and migration rate of current ripples were almost identical when scaled, thus verifying that exact Reynolds-Froude modelling of loose-sediment transport is valid and workable. Modelling should be valid as well for a wide range of other transport conditions in the same kind of flow, because no additional kinds of forces or effects would be present in transport of loose grains in modes other than as ripples. In scaled-down modelling, a scale ratio of 2.5 is attainable without recourse to exotic fluids by use of water at 85°C to model natural flows at 10°C.  相似文献   

基于典型地质特征分析的大同盆地V_S30预测研究     

张龙飞  董斌  史琳娜 《震灾防御技术》2020,15(1):102-113

土体剪切波速是进行土层地震反应分析的动力学参数，对场地地震动参数确定具有重要意义。基于地质地貌分析，将大同盆地划分为5类典型地质单元。对盆地1429个钻孔剪切波速资料进行分析，探讨V_S30与V_S20的相关性，研究土体埋深、岩性、地质单元、标贯击数及密实度等地质特征对V_S的影响，并基于地质单元、剪切波速比、密实度系数及第四系上部覆盖层厚度相关性分析给出土体V_S30预测模型。研究结果表明，基于典型地质特征的V_S30预测模型拟合优度R2>0.90，预测精度很高，对于离散性较大、直接拟合估算较差及无剪切波速场地来说，以区分地质单元及土体类型的方式进行V_S30分解预测是良好的研究思路。首次在区分地质单元及土体类型的前提下提出剪切波速比及密实度系数，并将其与第四系上部覆盖层厚度综合应用于V_S30预测研究。研究结果可为大同盆地城市防震减灾规划、震害预测、区域性地震安全评价提供重要技术支撑。  相似文献   

Dynamic Response of Shallow-Buried Tunnels Traversing High Loess Slopes     

SUN Wen  LIANG Qingguo  WANG Lili  CAO Xiaoping 《中国地震研究》2020,34(4):496-509

Considering the existence of numerous shallow-buried tunnels traversing high slopes in the loess area in western China and the fact of high seismic intensity there, we investigate the dynamic response rules of a shallow-buried loess tunnel and its slope under the action of seismic waves with different intensities. Through large-scale shaking table model tests,we successfully analyze the characteristics and process of the destabilization of tunnels and slopes, and propose valuable suggestions regarding the reinforcement parts of a tunnel for reducing seismic damage. The results show that the main seismic damage on a slope include the failure of the sliding surface between the top and foot and the stripping of the soil around the tunnel entrance, while the damage on a tunnel is mainly manifested as the seismic-induced subsidence at the portal section and the cracking deformation at the joint areas. Finally,we propose that the "staggered peak distribution" phenomenon of the maximum acceleration values at the vault and inverted arch area can be considered as a criterion indicating that the tunnel enters into the threshold of dynamic failure.  相似文献   

GPS技术在县级土地利用动态监测中的应用   总被引：10，自引：0，他引：10  

王晓栋  崔伟宏 《遥感学报》1999,3(4):318-323

准确、定量地把握土地利用及其变化状况具有重要的意义。全球定位系统（ＧＰＳ） 在土地利用动态监测中既是遥感技术的辅助定位手段,也可以作为独立的数据获取手段。介绍了ＧＰＳ定位方式和特点,结合中国国家“九五”攻关项目,讨论了县级土地利用动态监测中的ＧＰＳ选型思路和综合考虑ＧＩＳ功能的ＧＰＳ数据获取方法。通过实验证明了２Ｄ异常数据处理方法和ＧＰＳ数据处理中“假５４”代替“真５４”的可行性。这些结论将有效地提高内、外业工作效率和数据精度。  相似文献   

East African topography and volcanism explained by a single,migrating plume     

《地学前缘(英文版)》2020,11(5):1669-1680

Anomalous topographic swells and Cenozoic volcanism in east Africa have been associated with mantle plumes.Several models involving one or more fixed plumes beneath the northeastward migrating African plate have been suggested to explain the space-time distribution of magmatism in east Africa.We devise paleogeographically constrained global models of mantle convection and,based on the evolution of flow in the deepest lower mantle,show that the Afar plume migrated southward throughout its lifetime.The models suggest that the mobile Afar plume provides a dynamically consistent explanation for the spatial extent of the southward propagation of the east African rift system(EARS),which is difficult to explain by the northeastward migration of Africa over one or more fixed plumes alone,over the last≈45 Myr.We further show that the age-progression of volcanism associated with the southward propagation of EARS is consistent with the apparent surface hotspot motion that results from southward motion of the modelled Afar plume beneath the northeastward migrating African plate.The models suggest that the Afar plume became weaker as it migrated southwards,consistent with trends observed in the geochemical record.  相似文献   

基于双桥静力触探的饱和砂土液化判别方法刍议     

孙君  韩琪 《地质灾害与环境保护》2020,(1):87-92

饱和砂土液化是地震引发地基变形失稳、建筑受损破坏的主因之一,合理判定液化可能性是勘察实践和理论研究的重大课题。国内规范要求砂土液化判别仍以标准贯入试验为主,静力触探等原位测试方法为辅,静力触探较其他原位测试手段,在操作便利性、数据采集连续性、测试成本和抗干扰能力等方面更具优势。针对国内规范常用静力触探砂土液化判别方法进行了分析研究,并结合勘察实例进行了计算和对比,探讨了静力触探判别液化方法的土层适用性,并提出有关改进建议。  相似文献   

顺层蠕动边坡变形破坏机理及稳定性动态分析   总被引：11，自引：5，他引：11  

杨天鸿  芮勇勤  李连崇  马新民  申力 《工程地质学报》2003,11(2):155-161

本文以阜新海州露天矿边坡为例, 分析了边坡变形规律和破坏机制。在弱层流变试验的基础上, 建立了弱层流变力学模型, 通过确定加速蠕变阶段来临的极限应变量和应变速率, 建立了弱层长期强度的时间效应方程, 对于不同边坡工况进行了动态稳定性评价, 为采取抗滑措施控制蠕动边坡的变形破坏发展提供了科学依据。最后提出了一个边坡加速蠕变阶段来临的预测预报方法, 分析结果和实测资料较为一致。  相似文献   

《地理信息系统》空间分析教学动态演示系统开发     

王永波  杜培军  盛业华 《四川测绘》2003,26(3):134-137

针对《地理信息系统》课程教学中空间分析部分的特点，以优化教学效果为目标，探讨了CAI在空间分析教学中应用的模式，提出开发专用的小型动态演示系统的思路，并对系统设计中的相关问题进行了分析，最后以缓冲区分析动态演示为例说明了系统开发实现和应用效果。  相似文献   

河南省2002—01—12雷暴成因探析     

王蕊苏爱芳  李保生 《河南气象》2003,(2):10-11

利用实时资料，分析了2002—01—12河南省雷暴产生前后的大气能量和动力条件，揭示了雷暴的成因。  相似文献