Paramater regimes for studying isolated eddies     

Peter D. Killworth  Michael K. Davey 《地球物理与天体物理流体动力学》2013,107(4):225-264

Abstract

The parameter ranges relevant to propagating oceanic eddies are explored with a view to simplifying the equation sets previously used to simulate such eddies. The reduced gravity shallow-water model is used as a starting point. We consider eddies whose width is of the same order as, or somewhat larger than, the Rossby deformation radius. Two model equations emerge from these scalings, both permitting modon solutions and easy numerical integration. Both, too, give fair simulations of the shallow-water model, but disagree in details.

Using another approach, an ad hoc vortex model is used to predict the path of an eddy. This also gives a fair but not perfect simulation of the one-layer results. It appears that the only ideal way to reproduce primitive equation results accurately is to use the primitive equations themselves.  相似文献   

考虑关断时间的回线源激发TEM三维时域有限差分正演   总被引：14，自引：9，他引：5       下载免费PDF全文

孙怀凤  李貅  李术才  戚志鹏  王祎鹏  苏茂鑫  薛翊国  刘斌 《地球物理学报》2013,56(3):1049-1064

从麦克斯韦旋度方程出发可以直接导出瞬变电磁场扩散方程,然而扩散方程不含电场对时间的一阶导数,不能构成显式的时域有限差分方程,借鉴du Fort-Frankel有限差分离散方法引入虚拟位移电流项构建显式时域有限差分方程.对Wang和Hohmann的经典时域算法进行了两点改进:第一,通过将矩形回线源电流密度加入麦克斯韦方程组的安培环路定理方程,实现回线源瞬变电磁激发源加入;第二,在计算中考虑关断时间.第一点改进使时域有限差分方程考虑了一次场的计算,并且源的计算不再依赖均匀半空间模型响应作为初始条件,使算法能够适应表层电阻率不均匀时的三维复杂模型.由于实际观测中不可能出现阶跃电流的关断形式,第二点改进可以方便设置发射电流下降沿.采用改进的三维时域有限差分正演算法对均匀半空间模型、四类三层模型、均匀半空间中含有低阻块体模型进行了计算并分别与解析解、线性数字滤波解、积分方程解和Wang的三维时域有限差分解进行了对比验证.以H模型为例,采用建立的三维时域有限差分正演算法计算了不同关断时间的斜阶跃脉冲回线源瞬变电磁中心点感应电动势衰减曲线.以实际地质资料为基础,构建包含两层采空区的三维复杂模型,以1 μs的极短关断时间进行了复杂模型定回线源瞬变电磁响应计算,并计算了该复杂模型的视电阻率曲线.  相似文献   

基于尺度变换随机共振的瞬变电磁弱信号检测   总被引：1，自引：0，他引：1       下载免费PDF全文

王国富  张海如  张法全  叶金才 《地球物理学报》2011,54(7):1928-1934

晚期瞬变电磁信号是大参数、多频率、且各频率分量未知的电磁信号,特别在晚期还是强噪声背景下的微弱信号.随机共振系统可以在极限信噪比的情况下提取微弱信号,但仅适用于小参数、单一频率或频率已知的高频信号的情况,为此,本文提出一种基于尺度变换的随机共振算法用于检测晚期瞬变电磁信号,该方法充分利用了随机共振检测弱信号的优势,通过...  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987111000181     

Ka-Kheng Tan  Rex B. Thorpe  Zhidan Zhao 《地学前缘(英文版)》2011,2(2):223-235

This study investigates the mechanism of formation of convection plumes of mushroom shape in sub-solidus mantle and their prediction.The seismic-tomographic images of columnar structures of several hundreds kilometers in diameter have been reported by several researchers,while the much cherished mushroom-shaped plume heads could only be found in computational geodynamics(CGD) models and simple small-scale laboratory analogue simulations.Our theory of transient instability shows that the formation of conv...  相似文献   

Simulated eddy induced vertical velocities in a Gulf of Alaska model     

Shannon H. Nudds  Jennifer A. Shore 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(11):1060-1068

Mesoscale eddies can distribute nutrients, heat and fresh water into the Gulf of Alaska (GOA) from the coastal margins. While many studies have investigated the physical characteristics of GOA eddies, their effects on passive-dispersive particles have not been previously simulated to investigate eddy induced upwelling. A climatologically forced Parallel Ocean Program simulation of the north Pacific Ocean with an online particle tracking scheme was used to simulate passive-dispersive particles in the Gulf of Alaska. In-eddy vertical Lagrangian velocities of the particles were calculated both inside and outside the eddies and showed upwelling rates are generally greater inside the eddies where the vertical velocities of the particles ranged from 0.2 to 0.7 m/day.  相似文献   

用大功率长偏移距瞬变电磁测深圈定深层碳酸盐岩储层     

何青松 《地质与勘探》2013,49(4):731-736

中国西部T盆地ZY构造带在TY2井5900m深层发现下古高产储层,但由于地表复杂、地震物性条件差,一直难以有效的查明白云岩储层的分布;为此本文在该区开展了大功率长偏移距瞬变电磁(LOTEM)测深勘探,并取得了良好效果。本文介绍了沙漠区大功率LOTEM测深法工作原理和资料处理解释中剩余异常的求取和测井微电性层对比解释方法,展示了用大功率LOTEM测深法研究白云岩储层的成果,表明大功率LOTEM测深法对ZY构造带深层高阻碳酸盐岩中的低阻白云岩储层研究是有效的。该方法可以在类似物性条件下的其它地区作为储层研究的有效手段推广应用。  相似文献   

2013年12月华东地区持续性霾天气成因分析     

潘劲松  李超 《气候与环境研究》2020,25(1):55-63

2013年12月华东地区发生历史罕见的超过20 d连续重度霾天气过程。本文利用NCEP/NCAR再分析资料、华东地区大气细颗粒浓度资料以及常规气象观测资料对此次天气过程的环流形势、持续机制和前期外强迫因子展开分析。结果表明，此次华东连续重度霾天气和东亚中高纬阻塞高压活动密切相关。2013年12月白令海到鄂霍茨克海阻塞活动加强导致东亚地区天气瞬变扰动异常偏弱，贝加尔湖东侧弱高空脊长时间维持，我国东部地区受弱偏北风影响，大气扩散条件较差，有利于华东本地大气细颗粒物积累和北方霾粒子向华东地区输送。进一步研究表明2013年12月鄂霍茨克海阻塞高压活动偏强可能和前期热带印度洋暖海温异常有关。  相似文献   

瞬变电磁法的探测深度问题   总被引：9，自引：1，他引：8       下载免费PDF全文

闫述  石显新  陈明生 《地球物理学报》2009,52(6):1583-1591

用解析分析、时域有限差分、时-频分析的方法,以地面中心回线装置和阶跃脉冲激励源为例,分析讨论了瞬变电磁测深法的勘探深度问题,以便为野外勘探工作设计提供依据,达到预期的探测目的.解析计算证实了瞬变场在地下以有限速度传播,数值模拟表示出了准静态条件下瞬变场的反射.研究结果表明,由于时间域电磁场遵循因果律,瞬变电磁法的探测深度主要由观测时间决定. 瞬变电磁场的初始传播速度与大地电阻率无关,继后在大地色散作用下,阶跃脉冲前沿逐渐变得平缓,各频率分量的传播速度与电阻率有关,在低阻地层中探测同样的深度需要较长的观测时间. 最大探测深度是在给定时间内电磁波往返地下某一深度的单程距离,最小探测深度受仪器性能的限制,但是埋藏较浅的异常体也有可能在晚时段被观测到.从时-频密度谱中可得到瞬变电磁场信号时间与频率的关系.  相似文献   

Application of implicit sub-time stepping to simulate flow and transport in fractured porous media     

Y.-J. Park  E.A. Sudicky  S. Panday  J.F. Sykes  V. Guvanasen 《Advances in water resources》2008

In general, the accuracy of numerical simulations is determined by spatial and temporal discretization levels. In fractured porous media, the time step size is a key factor in controlling the solution accuracy for a given spatial discretization. If the time step size is restricted by the relatively rapid responses in the fracture domain to maintain an acceptable level of accuracy in the entire simulation domain, the matrix tends to be temporally over-discretized. Implicit sub-time stepping applies smaller sub-time steps only to the sub-domain where the accuracy requirements are less tolerant and is most suitable for problems where the response is high in only a small portion of the domain, such as within and near the fractures in fractured porous media. It is demonstrated with illustrative examples that implicit sub-time stepping can significantly improve the simulation efficiency with minimal loss in accuracy when simulating flow and transport in fractured porous media. The methodology is successfully applied to density-dependent flow and transport simulations in a Canadian Shield environment, where the flow and transport is dominated by discrete, highly conductive fracture zones.  相似文献   

Atmospheric Response to Mesoscale Ocean Eddies over the South China Sea     

Haoya LIU  Weibiao LI  Shumin CHEN  Rong FANG  Zhuo LI 《大气科学进展》2018,35(9):1189-1204

The South China Sea(SCS) is an eddy-active area. Composite analyses based on 438 mesoscale ocean eddies during 2000–2012 revealed the status of the atmospheric boundary layer is influenced remarkably by such eddies. The results showed cold-core cyclonic(warm-core anticyclonic) eddies tend to cool(warm) the overlying atmosphere and cause surface winds to decelerate(accelerate). More than 5% of the total variance of turbulent heat fluxes, surface wind speed and evaporation rate are induced by mesoscale eddies. Furthermore, mesoscale eddies locally affect the columnar water vapor, cloud liquid water, and rain rate. Dynamical analyses indicated that both variations of atmospheric boundary layer stability and sea level pressure are responsible for atmospheric anomalies over mesoscale eddies. To reveal further details about the mechanisms of atmospheric responses to mesoscale eddies, atmospheric manifestations over a pair of cold and warm eddies in the southwestern SCS were simulated. Eddy-induced heat flux anomalies lead to changes in atmospheric stability. Thus, anomalous turbulence kinetic energy and friction velocity arise over the eddy dipole, which reduce(enhance) the vertical momentum transport over the cold(warm) eddy, resulting in the decrease(increase) of sea surface wind. Diagnoses of the model's momentum balance suggested that wind speed anomalies directly over the eddy dipole are dominated by vertical mixing terms within the atmospheric boundary layer, while wind anomalies on the edges of eddies are produced by atmospheric pressure gradient forces and atmospheric horizontal advection terms.  相似文献