南大洋混合层的时空变化特征     

应美佳  刘海龙  王夫常  张召儒  钟贻森 《海洋与湖沼》2019,50(6):1223-1232

过去对南大洋的研究受限于长期观测的缺乏,而现在地转海洋学实时观测阵(Arrayfor Real-timeGeostrophicOceanography,Argo)项目自开始以来持续提供了高质量的温度盐度观测,使系统地研究南大洋海洋上层结构成为可能。本研究使用2000—2018年的Argo浮标观测数据,分析了南大洋混合层深度(Mixed Layer Depth, MLD)的时空分布特征。结果表明:南大洋混合层存在明显的季节变化,冬春两季MLD在副南极锋面北侧达到最高值并呈带状分布,夏秋两季由于海表加热导致混合层变浅,季节变化幅度达到400m以上;在年际尺度上,MLD受南半球环状模(Southern HemisphereAnnularMode,SAM)调制,呈现纬向不对称空间分布特征,这与前人结果一致;本文指出在所研究时段,南大洋混合层在90°E以东,180°以西有加深趋势,而在60°W以西,180°以东有变浅趋势,显示出偶极子分布特征,并且这种趋势特征主要是风场的作用。  相似文献   

The multi-component Hekla Ö Tephra,Iceland: a complex widespread mid-Holocene tephra layer     

Daníel Freyr Jónsson  Esther Ruth Gudmundsdóttir  Gudrún Larsen  Bergrún Arna Óladóttir  Egill Erlendsson  Sigrún Dögg Eddudóttir  Olgeir Sigmarsson 《第四纪科学杂志》2020,35(3):410-421

Large Plinian eruptions from Hekla volcano, Iceland, produce compositionally zoned tephra used as key markers in tephrochronology. However, spatial variations in chemical composition of a tephra layer may complicate its identification. An example is the 5950–6180 cal a bp Hekla Ö tephra layer, which shows compositional spread from rhyolite, dacite and andesite to basalt. In soil sections north of Hekla, the SiO₂ content of the tephra glass reaches 76 wt% in the lowest unit of the Hekla Ö deposit and decreases to 62–63 wt% in the uppermost unit. Intermingled within the whole deposit are basalt tephra grains having 46–47 wt% SiO₂. The composition of the basalt glass includes primitive basalt and a more evolved basalt (MgO >6 and <6 wt%, respectively). Together with literature data, the Hekla Ö tephra and the so-called T-Tephra/Hekla-T are most likely from contemporaneous eruptions of different vents on the Hekla volcanic system, forming a single important marker tephra (Hekla ÖT) deposited over 80% of Iceland. Identification is complicated by its spatial compositional heterogeneity, such as systematic decrease in SiO₂ content from the east to the west of Hekla volcano. Consequently, an individual tephra layer from a large explosive eruption can have different composition at different locations. © 2020 John Wiley & Sons, Ltd.  相似文献   

Modelling spatial variations in dissolved oxygen in fine‐grained streams under uncertainty          下载免费PDF全文

Vahid Zahraeifard  Zhiqiang Deng  Ronald Malone 《水文研究》2015,29(2):212-224

This paper presents a novel triple‐layer model, called VART DO‐3L, for simulation of spatial variations in dissolved oxygen (DO) in fine‐grained streams, characterized by a fluid mud (fluff or flocculent) layer (an advection‐dominated storage zone) as the interface between overlying stream water and relatively consolidated streambed sediment (a diffusion‐dominated storage zone). A global sensitivity analysis is conducted to investigate the sensitivity of VART DO‐3L model input parameters. Results of the sensitivity analysis indicate that the most sensitive parameter is the relative size of the advection‐dominated storage zones (A_s/A), followed by a lumped reaction term (R) for the flocculent layer, biological reaction rate (μ_o) in diffusive layer and biochemical oxygen demand concentration (L) in water column. In order to address uncertainty in model input parameters, Monte Carlo simulations are performed to sample parameter values and to produce various parameter combinations or cases. The VART DO‐3L model is applied to the Lower Amite River in Louisiana, USA, to simulate vertical and longitudinal variations in DO under the cases. In terms of longitudinal variation, the DO level decreases from 7.9 mg l at the Denham Springs station to about 2.89 mg l^?1 at the Port Vincent station. In terms of vertical variation, the DO level drops rapidly from the overlying water column to the advection‐dominated storage zone and further to the diffusive layer. The DO level (C_F) in the advective layer (flocculent layer) can reach as high as 40% of DO concentration (C) in the water column. The VART DO‐3L model may be applied to similar rivers for simulation of spatial variations in DO level. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Comparison of runoff characteristics of two adjacent basins in a tropical rainforest using a modified hydrologic cycle model with outflow          下载免费PDF全文

Taeko Wakahara  Katsushige Shiraki  Masakazu Suzuki 《水文研究》2014,28(3):509-520

We propose a new runoff model including an outflow process that was applied to two adjacent basins (CL, TL) located in Lambir Hills National Park in north‐central Sarawak, Malaysia. Rainfall, runoff, topography, and soil layer thickness were observed. About 19% of annual runoff was observed in the CL basin (21.97 ha), whereas about 46% was observed in the TL basin (23.25 ha). It was inferred that the CL basin has an outflow because of low base flow, small runoff peak, and excessive water loss. By incorporating the outflow process into the HYdrological CYcle MODEL, good agreement between the data generated by the model and that observed was shown, with the exception of the data from the rainless period. Then, the fitting parameters for each basin were exchanged, except for the outflow parameter, and the characteristics of each basin were compared by calculating virtual runoff. As a result, the low base flow of the CL basin was estimated by the movement of the rainwater that escaped from the basin as deep percolation or lateral flow (11% of rainfall). The potential of the CL basin for mitigating flood and drought appeared to be higher than that of the TL basin. This is consistent with the topographic characteristics of the CL basin, which has a gentler slope than the TL basin. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Analytical layer‐element method for non‐axisymmetric consolidation of multilayered soils     

Zhi Yong Ai  Wen Ze Zeng 《国际地质力学数值与分析法杂志》2012,36(5):533-545

A numerically efficient and stable method is developed to analyze Biot's consolidation of multilayered soils subjected to non‐axisymmetric loading in arbitrary depth. By the application of a Laplace–Hankel transform and a Fourier expansion, the governing equations are solved analytically. Then, the analytical layer‐element (i.e. a symmetric stiffness matrix) describing the relationship between generalized displacements and stresses of a layer is exactly derived in the transformed domain. Considering the continuity conditions between adjacent layers, the global stiffness matrix of multilayered soils is obtained by assembling the inter‐related layer‐elements. Once the solution in the Laplace–Hankel transformed domain that satisfies the boundary conditions has been obtained, the actual solution can be derived by the inversion of the Laplace–Hankel transform. Finally, numerical examples are presented to verify the theory and to study the influence of the layered soil properties and time history on the consolidation behavior. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Steady‐state analytical solutions of flow and deformation coupling due to a point sink within a finite fluid‐saturated poroelastic layer          下载免费PDF全文

P. Li  K. Wang  G. Fang  D. Lu 《国际地质力学数值与分析法杂志》2017,41(8):1093-1107

An exact steady‐state closed‐form solution is presented for coupled flow and deformation of an axisymmetric isotropic homogeneous fluid‐saturated poroelastic layer with a finite radius due to a point sink. The hydromechanical behavior of the poroelastic layer is governed by Biot's consolidation theory. Boundary conditions on the lateral surface are specifically chosen to match the appropriate finite Hankel transforms and simplify the transforms of the governing equations. Ordinary differential equations in the transformed domain are solved, and then the analytical solutions in the physical space for the pore pressure and the displacements are finally obtained by using finite Hankel inversions. The analytical solutions at some special locations such as the top and bottom surfaces, lateral surface, and the symmetrical axis are given and analyzed. And a case study for the consolidation of a water‐saturated soft clay layer due to pumping is conducted. The analytical solution is verified against the finite element solution. Meanwhile, an analysis of coupled hydromechanical behavior is carried out herein. The presented analytical solution is an exact solution to the practical poroelastic problem within an axisymmetric finite layer. It can provide us a better understanding of the poroelastic behavior of the finite layer due to fluid extraction. Besides, it can be applied to calibrate numerical schemes of axisymmetric poroelasticity within finite domains. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Probabilistic Approach of Coastal Defense Against Typhoon Attacks for Nuclear Power Plant     

刘德辅  韩凤亭  庞亮  李华军  谢波涛  王风清 《中国海洋工程》2010,24(2):265-275

With the global wanning and sea level rising, it is widely recognized that there is an increasing tendency of typhoon occurrence frequency and intensity. The defenses code against typhoon attacks for nuclear power plant should be calibrated because of the increasing threat of typhoon disaster and severe consequences. This paper discusses the probabilistic approach of definitions about "probable maximum typhoon" and "probable maximum storm surge" in nuclear safety regulations of China and has made some design code calibrations by use of a newly proposed Double Layer Nested Multi-objective Probability Model (DLNMPM).  相似文献   

Role of buffer layer in electronic structures of iron phthalocyanine molecules on Au(111)     

孙家涛  潘理达  胡昊  杜世萱  高鸿钧 《海洋学报(英文版)》2010,29(9)

We investigate the electronic structures of one and two monolayer iron phthalocyanine (FePc) molecules on Au(111) surfaces. The first monolayer FePc is lying flat on the Au(111) substrate, and the second monolayer FePc is tilted at ～15° relative to the substrate plane along the nearest neighbour [101^-] direction with a lobe downward to the central hole of the unit cell in the first layer. The structural information obtained by first-principles calculations is in agreement with the experiment results. Furthermore, it is demonstrated that the electronic structures of FePc molecules in one-monolayer FePc/Au(111) system are perturbed significantly, while the electronic structures of FePc molecules in the second monolayer in two-monolayer FePc/Au(111) system remain almost unchanged due to the screening of the buffer layer on Au(111).  相似文献   

The impact of highly permeable layer on hydraulic system in a coastal aquifer     

Kue‐Young Kim  Weon Shik Han  Eungyu Park 《水文研究》2013,27(22):3128-3138

This study is aimed to understand the hydraulic mechanism of coastal aquifer systems that include highly permeable layers (HPLs). These hydrologic conditions can be found in many volcanic islands that are composed of a series of lava flows discharged into sea or other standing body of water. In the first part, we developed a numerical model based on the geologic and hydrologic data obtained from the eastern Jeju Island, Korea, of which the aquifer contains clinker and hyaloclastite layers. The simulation results reproduced spatial location of fresh‐saline water interface, especially the abrupt decline of interface at the inland part and the thickness variation of transition zone along the cross‐section observed at the eastern Jeju coastal aquifer. We were able to find out that these phenomena are strongly related to the presence of the HPL. In the second part, quantitative analyses were conducted with the use of hypothetical models in order to understand the dynamic characteristics of coastal system that includes HPLs. A series of sensitivity studies were conducted to assess the effect of the horizontal length and vertical depth of HPL on the spatial location of the interface toe and the configuration of transition zone. Various case studies have shown that the seawater intruded into the inland more as the horizontal length of HPL was increased and its vertical depth was decreased. In other simulations including two HPLs, the vertical distance between these two HPLs primarily controlled the flow regime, flux variations, and the configuration of the transition zone. Finally, we performed simulations to evaluate the effect of a rising sea‐level. This study provides more understanding of how the presence of HPL controls the seawater intrusion processes, and the spatial configurations of fresh‐saline water interface at coastal aquifers. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Tests and applications of an approach to absorbing reflected waves towards incident boundary     

张洪生  王炎  许春辉  商辉  于小伟 《中国海洋工程》2013,27(6):703-718

If the upstream boundary conditions are prescribed based on the incident wave only, the time-dependent numerical models cannot effectively simulate the wave field when the physical or spurious reflected waves become significant. This paper describes carefully an approach to specifying the incident wave boundary conditions combined with a set sponge layer to absorb the reflected waves towards the incident boundary. Incorporated into a time-dependent numerical model, whose governing equations are the Boussinesq-type ones, the effectiveness of the approach is studied in detail. The general boundary conditions, describing the down-wave boundary conditions are also generalized to the case of random waves. The numerical model is in detail examined. The test cases include both the normal one-dimensional incident regular or random waves and the two-dimensional oblique incident regular waves. The calculated results show that the present approach is effective on damping the reflected waves towards the incident wave boundary.  相似文献