Effects of mesoscale sea-surface temperature fronts on the marine atmospheric boundary layer   总被引：1，自引：0，他引：1  

Eric D. Skyllingstad  Dean Vickers  Larry Mahrt  Roger Samelson 《Boundary-Layer Meteorology》2007,123(2):219-237

A numerical modelling study is presented focusing on the effects of mesoscale sea-surface temperature (SST) variability on surface fluxes and the marine atmospheric boundary-layer structure. A basic scenario is examined having two regions of SST anomaly with alternating warm/cold or cold/warm water regions. Conditions upstream from the anomaly region have SST values equal to the ambient atmosphere temperature, creating an upstream neutrally stratified boundary layer. Downstream from the anomaly region the SST is also set to the ambient atmosphere value. When the warm anomaly is upstream from the cold anomaly, the downstream boundary layer exhibits a more complex structure because of convective forcing and mixed layer deepening upstream from the cold anomaly. An internal boundary layer forms over the cold anomaly in this case, generating two distinct layers over the downstream region. When the cold anomaly is upstream from the warm anomaly, mixing over the warm anomaly quickly destroys the shallow cold layer, yielding a more uniform downstream boundary-layer vertical structure compared with the warm-to- cold case. Analysis of the momentum budget indicates that turbulent momentum flux divergence dominates the velocity field tendency, with pressure forcing accounting for only about 20% of the changes in momentum. Parameterization of surface fluxes and boundary-layer structure at these scales would be very difficult because of their dependence on subgrid-scale SST spatial order. Simulations of similar flow over smaller scale fronts (<5 km) suggest that small-scale SST variability might be parameterized in mesoscale models by relating the effective heat flux to the strength of the SST variance.  相似文献   

Tidally dominated, rimmed-shelf facies of the Picún Leufú Formation (Jurassic/Cretaceous boundary) in southwest Gondwana, Neuquén Basin, Argentina     

Claudia Armella  Nora Cabaleri  Hctor A. Leanza 《Cretaceous Research》2007,28(6):961-979

A palaeoenvironmental model for the Picún Leufú Formation (Jurassic/Cretaceous boundary), which crops out in the Neuquén Basin, Argentina, on the southwestern margin of Gondwana, is presented in this paper for the first time. Detailed stratigraphic sections exposed along National Road 40 where it crosses the Picún Leufú Creek (type locality) and in the Cerrito Caracoles area, were examined and sampled. Based on a combination of the sedimentological data obtained (facies/microfacies analysis) and the relationship between benthic macrofaunas and their taphonomic attributes, it is concluded that the formation reflects a tidally dominated, rimmed-shelf setting characterized by prograding bars dissected by channels and thick lagoonal facies with shoal developments. In the Cerrito Caracoles area, where only the basal part of the formation is exposed, it is interpreted to have been deposited in a shallow subtidal marine environment in which shelf margin facies with patch reefs have been recognized.  相似文献   

A Comparison between a Modified Counter Propagation Network and an Extended Self-Organizing Map in Remotely Sensed Data Classification     

Yongliang Chen  Micha I. Pazner  Wei Wu 《Mathematical Geology》2007,39(6):559-574

A modified counter propagation network model and an extended self-organizing map model have the same three-layer network architecture while employing slightly different learning rules. Their network architecture comprises an input layer, a Kohonen layer and an output layer. The neurons between two neighboring layers are fully connected and the neighboring neurons within the Kohonen layer also have neighborhood connections. The modified counter propagation network model employs the Kohonen algorithm to train the Kohonen layer while using the Widrow–Hoff rule to train the output layer. However, the extended self-organizing map model applies a modified Kohonen’s learning rule to train both the Kohonen layer and the output layer. This paper compares the performances of these two models in supervised classification of remotely sensed data. The training results show that compared to the extended self-organizing map model, the modified counter propagation model has faster learning speed but larger output errors. The classification results indicate that the extended self-organizing map model has a faster classification speed and a much higher classification precision than the modified counter propagation model.  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   

A computational method for approximating a Darcy–Stokes system governing a vuggy porous medium     

Todd Arbogast  Dana S. Brunson 《Computational Geosciences》2007,11(3):207-218

We develop and analyze a mixed finite element method for the solution of an elliptic system modeling a porous medium with large cavities, called vugs. It consists of a second-order elliptic (i.e., Darcy) equation on part of the domain coupled to a Stokes equation on the rest of the domain, and a slip boundary condition (due to Beavers–Joseph–Saffman) on the interface between them. The tangential velocity is not continuous on the interface. We consider a 2-D vuggy porous medium with many small cavities throughout its extent, so the interface is not isolated. We use a certain conforming Stokes element on rectangles, slightly modified near the interface to account for the tangential discontinuity. This gives a mixed finite element method for the entire Darcy–Stokes system with a regular sparsity pattern that is easy to implement, independent of the vug geometry, as long as it aligns with the grid. We prove optimal global first-order L ² convergence of the velocity and pressure, as well as the velocity gradient in the Stokes domain. Numerical results verify these rates of convergence and even suggest somewhat better convergence in certain situations. Finally, we present a lower dimensional space that uses Raviart–Thomas elements in the Darcy domain and uses our new modified elements near the interface in transition to the Stokes elements.  相似文献   

An immersed boundary method for compressible multiphase flows: application to the dynamics of pyroclastic density currents     

Mattia de’ Michieli Vitturi  Tomaso Esposti Ongaro  Augusto Neri  Maria Vittoria Salvetti  François Beux 《Computational Geosciences》2007,11(3):183-198

  相似文献   

Application of micromagnetic mapping for defining geological and anthropogenic heterogeneities in recent coastal sediments of the Ekspeditsii Bay (Petr Velikii Gulf, Sea of Japan)     

E. A. Bessonova 《Russian Journal of Pacific Geology》2007,1(6):537-549

The comprehensive analysis of the multiparameter and diverse information made it possible to reconstruct sedimentation patterns in the coastal zone of the Ekspeditsii Bay at the recent development stage of the geological environments. Geological and anthropogenic sources of the anomalous magnetic field are distinguished based on the measured module of a complete magnetic field vector. It is inferred that sedimentary material constituting the cultural layer in the Kraskino site of the ancient settlement that represents the largest archeological monument of the Bohai State in the Primorye region originates from different sources. The internal topography of the cultural layer of the medieval flat site of the ancient settlement is first reconstructed in the southern Russian Far East based on a micromagnetic survey with defining of the most informative objects important for understanding the cultural-historical development of the archaeological monument.  相似文献   

Subtropical to temperate facies from a transition zone, mixed carbonate–siliciclastic system, Palaeogene, North Carolina, USA     

BRIAN P COFFEY  J. FRED READ† 《Sedimentology》2007,54(2):339-365

Palaeogene passive margin sediments on the US mid‐Atlantic coastal plain provide valuable insight into facies interaction and distribution on mixed carbonate–siliciclastic shelves. This study utilizes well cuttings, outcrop, core, and seismic data to document temporal and spatial variations in admixed bryozoan‐rich skeletal carbonates and sandy siliciclastic units that were deposited on a humid passive margin located in the vicinity of a major marine transition zone. This zone was situated between north‐flowing, warm waters of the ancestral Gulf Stream (carbonate dominated settings) and south‐flowing, cold waters of the ancestral Labrador Current (siliciclastic dominated settings). Some degree of mixing of carbonates and siliciclastics occurs in all facies; however, siliciclastic‐prone sediments predominate in nearshore settings, while carbonate‐prone sediments are more common in more open marine settings of the inner shelf break and deep shelf. A distinctive dual‐break shelf depositional profile originated following a major Late Cretaceous to Palaeocene transgression that drowned the earlier shallow platform. This profile was characterized by prominent mid‐shelf break dividing the shallow shelf from the deep shelf and a major continental shelf/slope break. Incomplete filling of available accommodation space during successive buildup of the shallow shelf preserved the topographic break on this passive margin. Storm wave base also contributed to the preservation of the dual‐break shelf geometry by beveling shallow shelf sediments and transporting them onto and seaward of the mid‐shelf break. Sediment fines in deep shelf facies were produced in place, transported downdip from the shallow shelf by storm ebb currents and boundary currents, and reworked from adjacent areas of the deep shelf by strike‐parallel boundary currents. Regional climate and boundary currents controlled whether carbonate or siliciclastic material was deposited on the shelf, with warmer waters and more humid climates favouring carbonate deposition and cooler, more arid conditions favouring glaucony and siliciclastic dominated deposition. Continuous wave and current sweeping of the shallow shelf favoured deposition of mud‐lean facies across much of the shallow shelf. Skeletal components in much of the carbonate‐rich strata formed in warm, nutrient‐rich subtropical waters, as indicated by widespread occurrences of larger benthic foraminifera and molluscan assemblages. These indicators of warm water deposition within the bryozoan‐mollusk‐rich carbonate assemblage on this shelf provide an example of a warm water bryomol assemblage; such facies generally are associated with cooler water depositional settings.  相似文献   

一次持续性强暴雨过程的平均特征   总被引：4，自引：1，他引：4       下载免费PDF全文

陈忠明闵文彬  高文良何光碧 《应用气象学报》2006,17(3):273-280

2004年9月2—6日四川盆地中东部发生了一次持续性强暴雨过程。利用时间平均合成分析方法对强暴雨维持期间 (9月3日20:00—5日08:00, 北京时) 的探测资料进行合成平均, 再对合成平均资料做诊断分析, 以揭示持续性强暴雨过程持续期的平均特征。诊断分析显示, 台风西进导致稳定的环流以及中低层大量的水汽输送为暴雨持续提供了背景条件。在时间平均流场上, 与暴雨相联系的中尺度系统十分显著, 它在对流层中低层表现为准东西向的中尺度辐合带, 在对流层高层表现为中尺度辐散带, 两者垂直耦合为深厚系统。此外, 在暴雨持续期间, 对流层低层大气运动表现出强烈的非平衡特征, 这种非平衡的动力强迫作用支撑着低层强辐合的维持。  相似文献   

东北地区降水与大气环流关系   总被引：6，自引：2，他引：6       下载免费PDF全文

贾丽伟李维京  陈德亮 《应用气象学报》2006,17(5):557-566

利用Lamb-Jenkinson大气环流分型方法, 将1951—2004年逐日的海平面气压场分型, 得到27种不同的环流型, 研究了大气环流型与我国东北地区降水的关系。给出了8种出现频率最高的主要环流型出现的规律及它们平均的环流形势, 分析了8种主要环流型下东北地区降水异常分布状况, 并选出东北地区资料齐全、有代表性的9个站点进行了深入细致地分析, 成功地建立了降水与环流型出现频率的统计关系, 并用此重建了9个代表站54年的降水序列。结果表明:Lamb-Jenkinson大气环流分型方法可以很好地应用于我国东北地区, 由此划分的环流型符合实际情况; 8种主要环流型与降水的空间分布特征有很好的对应关系; 所建立的9个代表站降水距平回归方程能够解释近54年各站的大部分降水变化, 进一步证明了东北地区降水与大气环流之间的密切关系。  相似文献