The role of diapycnal mixing for the equilibrium response of thermohaline circulation     

Rezwan Mohammmad  Johan Nilsson 《Ocean Dynamics》2004,54(1):54-65

Using a zonally averaged, one-hemispheric numerical model of the thermohaline circulation, the dependence of the overturning strength on the surface equator-to-pole density difference is investigated. It is found that the qualitative behavior of the thermohaline circulation depends crucially on the nature of the small-scale vertical mixing in the interior of the ocean. Two different representations of this process are considered: constant vertical diffusivity and the case where the rate of mixing energy supply is taken to be a fixed quantity, implying that the vertical diffusivity decreases with increasing stability of the water column. When the stability-dependent diffusivity parameterization is applied, a weaker density difference is associated with a stronger circulation, contrary to the results for a fixed diffusivity. A counterintuitive consequence of the stability-dependent mixing is that the poleward atmospheric freshwater flux, which acts to reduce the thermally imposed density contrast, strengthens the thermally dominated circulation and its attendant poleward heat transport. However, for a critical value of the freshwater forcing, the thermally dominated branch of steady states becomes unstable, and is succeeded by strongly time-dependent states that oscillate between phases of forward and partly reversed circulation. When a constant vertical diffusivity is employed, on the other hand, the thermally dominated circulation is replaced by a steady salinity-dominated state with reversed flow. Thus in this model, the features of the vertical mixing are essential for the steady-state response to freshwater forcing as well as for the character of flow that is attained when the thermally dominated circulation becomes unstable.Responsible Editor: Jin-Song von Storch  相似文献   

新疆博格达山分段及深浅构造转换关系   总被引：15，自引：1，他引：15  

李涛  王宗秀  周高志  柳永清  李寅 《地学前缘》2004,11(3):103-114

研究表明 ,天山及邻区自中生代以来一直处于热衰减状态 ,博格达山新生代再造山具有“冷隆升”性 ,盆山边界断裂多限于上地壳内 ,而非直通中地壳低速体甚至上地幔的“深大断裂”。造山带内的韧性剪切带是在古生代形成的 ,而不是再造山期的断裂 ,它对造山带隆升及盆山耦合无贡献 ,博格达山的隆升为复式背斜构造所支持。博格达山与准东的关系为背斜北翼与盆地平缓基底构成的挠曲构造 ,而不是被深大断裂分隔的断块。博格达山具有独特鲜明的分段性 ,造山带的两个弧形构造与新生代再生前陆盆地构成独特的“斜方对称”分布样式。以板条观点为指导 ,从盆山单元的平面配置关系和深浅构造转换关系入手 ,探讨了博格达山板内造山阶段的几何学和运动学分段性的成因 ,构建了盆山耦合模式  相似文献   

预测和控制深基坑变形的抗隆起稳定系数法   总被引：1，自引：0，他引：1  

谢小林  贾坚 《上海国土资源》2004,107(1):22-27

本文讨论了在软土基坑工程设计施工中所涉及到的抗隆起稳定系数的合理计算方法；通过对大量上海深基坑工程的计算分析并结合现场实测数据论证了利用抗隆起稳定系数进行基坑变形预测和控制的合理性，并提出了适用稳定系数法控制基坑变形的设计计算预测公式：δh/H～Ks关系式。  相似文献   

四川新康风化淋滤型海泡石的热相变研究   总被引：3，自引：0，他引：3  

王吉中  李胜荣  江永宏 《矿物学报》2004,24(1):55-60

以四川新康风化淋滤型海泡石为研究对象，利用X射线衍射分析和红外光谱分析技术，对海泡石的热相变过程及特征进行了研究。结果发现，四川新康风化淋滤型海泡石的相变过程与沉积型、热液型海泡石相变过程明显不同，其相变过程可以划分为两个阶段：800℃以下保持海泡石相；800℃以上海泡石相转化为斜顽辉石相。  相似文献   

Beds comprising debrite sandwiched within co-genetic turbidite: origin and widespread occurrence in distal depositional environments   总被引：11，自引：0，他引：11  

P. J. Talling  L. A. Amy†  R. B. Wynn‡  J. Peakall†  M. Robinson 《Sedimentology》2004,51(1):163-194

Co‐genetic debrite–turbidite beds occur in a variety of modern and ancient turbidite systems. Their basic character is distinctive. An ungraded muddy sandstone interval is encased within mud‐poor graded sandstone, siltstone and mudstone. The muddy sandstone interval preserves evidence of en masse deposition and is thus termed a debrite. The mud‐poor sandstone, siltstone and mudstone show features indicating progressive layer‐by‐layer deposition and are thus called a turbidite. Palaeocurrent indicators, ubiquitous stratigraphic association and the position of hemipelagic intervals demonstrate that debrite and enclosing turbidite originate in the same event. Detailed field observations are presented for co‐genetic debrite–turbidite beds in three widespread sequences of variable age: the Miocene Marnoso Arenacea Formation in the Italian Apennines; the Silurian Aberystwyth Grits in Wales; and Quaternary deposits of the Agadir Basin, offshore Morocco. Deposition of these sequences occurred in similar unchannellized basin‐plain settings. Co‐genetic debrite–turbidite beds were deposited from longitudinally segregated flow events, comprising both debris flow and forerunning turbidity current. It is most likely that the debris flow was generated by relatively shallow (few tens of centimetres) erosion of mud‐rich sea‐floor sediment. Changes in the settling behaviour of sand grains from a muddy fluid as flows decelerated may also have contributed to debrite deposition. The association with distal settings results from the ubiquitous presence of muddy deposits in such locations, which may be eroded and disaggregated to form a cohesive debris flow. Debrite intervals may be extensive (> 26 × 10 km in the Marnoso Arenacea Formation) and are not restricted to basin margins. Such long debris flow run‐out on low‐gradient sea floor (< 0·1°) may simply be due to low yield strength (? 50 Pa) of the debris–water mixture. This study emphasizes that multiple flow types, and transformations between flow types, can occur within the distal parts of submarine flow events.  相似文献   

Transformation of Residuals to Avoid Artifacts in Geostatistical Modelling with a Trend   总被引：1，自引：0，他引：1  

Oy Leuangthong  Clayton V. Deutsch 《Mathematical Geology》2004,36(3):287-305

Trend modelling is an important part of natural resource characterization. A common approach to account for a variable with a trend is to decompose it into a relatively smoothly varying trend and a more variable residual component. Then, the residuals are stochastically modelled independent of the trend. This decomposition can result in values outside the plausible range of variability, such as grades below zero or ratios that exceed 1.0. We transform the residuals conditional to the trend component to explicitly remove these complex features prior to geostatistical modelling. Back transformation of the modelled residual values allows the complex relations to be reproduced. A petroleum-related application shows the robustness of the proposed transformation. Furthermore, a mining application shows that when this conditional transformation is applied to the original variable, instead of the residual, simulated values are assured to be nonnegative.  相似文献   

基于非线性平差模型的坐标转换公式   总被引：4，自引：2，他引：4  

包欢 付子傲陈刚  王玉京 《测绘学院学报》2004,21(3):175-177

用线性近似法以及非线性参数估计法讨论了直角坐标系七参数转换模型，指出改进的Gauss-Newton方法具有理论严密、计算简洁、易于编程、精度较高等持点。对于处理类似坐标转换的非线性模型具有重要的理论和实践意义。  相似文献   

一种基于向量序结构关系的多值形态变换   总被引：1，自引：0，他引：1  

段汕  秦前清 《武汉大学学报(信息科学版)》2004,29(11):1012-1016

提出了一种向量型数据全序关系建立的一般方法，并以此为基础建立了多值形态变换的基本形式，并对其性质进行了讨论。多值形态变换作为数学形态学在多值图像空间中的扩展．具有与灰值形态变换类似的功能和作用，可有效地应用于多值图像的处理和目标形状特征的提取。  相似文献   

适用于大旋转角的三维基准转换的一种简便模型   总被引：33，自引：0，他引：33  

陈义  沈云中  刘大杰 《武汉大学学报(信息科学版)》2004,29(12):1101-1105

基于大角度的空间直角坐标转换，提出了以方向余弦为参数、适用于任何角度旋转的空间直角坐标转换的简明计算方法。  相似文献   

基于Matlab的水准点稳定性分析   总被引：1，自引：0，他引：1  

姚占派  缑忠才 《现代测绘》2004,27(2):25-27

通过使用Matlab功能强大的数学软件，应用于测量工程的数据处理。具体解决变形监测中水准点是否稳定的判定问题。并通过计算实例说明其可行性和优越性。  相似文献