我国周边海域典型海洋锋特征建模研究     

卢晓亭  濮兴啸  李玉阳 《海洋科学》2013,37(6):37-41

基于海洋锋空间位置、水平分布结构和垂直扩展特征等时空特征参数,结合海洋锋空间结构几何模型,建立了区域海洋锋温盐三维结构快速重构特征模型,对黄海西部沿岸锋和东海黑潮中段锋锋区温度场进行了仿真计算,并与实测数据进行了比较分析,实验结果表明：仿真结果与实测数据符合较好,实验结果验证了特征模型的有效性和可推广性。海洋锋区声速具有明显的水平梯度变化,对声纳的水下探测和反探测产生显著影响,因此,需要建立实时估计获取锋区水下温、盐结构的方法。海洋锋特征模型能够快速有效地重构海洋锋区温度场,为实时获取海洋锋水下结构特征提供了方法。  相似文献   

用于成像光谱数据特征矿物识别的人工神经网络结构研究     

何勇强  姚国清 《国土资源遥感》2004,15(3):23-27

当某一问题很难甚至无法用数学方法建立精确模型时,人工神经网络的方法则显示了优势。对于一个具体问题,采用何种网络结构是至关重要的。本文以美国内华达州Cuprite矿区成像光谱数据特征矿物识别为例,采用6种不同结构的多层前馈网络模型,从其训练难度、运算效率及识别效果等方面进行了综合对比分析。  相似文献   

Wave propagation along freely propagating surface gravity current fronts     

Richard P. Mied  Arnold L. Cooper  Gloria J. Lindemann  Mark A. Sletten 《Dynamics of Atmospheres and Oceans》2002,36(1-3)

This work deals with the propagation and evolution of disturbances which move along freely propagating two-dimensional gravity current fronts. Examples of evolving perturbations on fronts are displayed in real-aperture radar images of gravity currents in the coastal zone. The theory of Cooper et al. (2001), which is based upon the ray tube formulation of Whitham (1974), is employed to simulate disturbances of the sort seen in this imagery and in the larger body of literature. Initial anomalies in both shape and velocity are introduced and allowed to evolve, and several types of new and interesting behaviors emerge. Shape perturbations of the form x=a sech δy evolve into two anomalies, which separate in time as they propagate in opposite directions along the front. When the value of a is increased, the disturbances, which propagate along the gravity current, can break, forming breaking frontal waves (BFWs). These manifest themselves as sharp angular features to either side of the main bulge. Two types of velocity disturbances are employed. The first has the form U=U₀(1+â sech δy), and evolves to preserve a single frontal bulge that increases in amplitude and width as it propagates. Here again, large values of â result in BFWs. In this case, they replicate the general behavior present in the imagery. The second type of velocity perturbation used is U=U₀(1+â cos δy). The smallest values of a generate no BFWs, but yield fronts which oscillate in space and time. Larger values produce a string of BFWs which are qualitatively similar to the cusp-and-trough morphology observed so frequently in nature. The largest values of a allow the gravity current to form a string of large, bulbous structures which intersect one another as they propagate forward and spread laterally. And finally, we make an effort to correlate the results of the simulations with the shapes seen in radar and visible imagery in the literature.  相似文献   

A Bulk Theory For Air Mass Motion Along A High Mountain Ridge     

Georgy I. Burde  Elena Morozovsky  Lev N. Gutman 《Boundary-Layer Meteorology》2002,103(2):177-204

A steady-state, spatial, large-scale, non-linear problemof the air massmotion along an undulating mountain ridge is consideredin the framework of bulktheory. The ridge is assumed to be so high that the airmass cannot top it, and, insteadof the actual ridge itself, a high vertical wall withsinuousities identical to those of theridge is considered. It is assumed that the air massis bounded above by an inversioninterface (idealized inversion layer) overlain by ageostrophic, polytropic, atmospherethat is thermally homogeneous along the horizontaland stably stratified with aconstant geostrophic wind blowing along the meandirection of the ridge. Theinversion strength (potential temperature deficit) isnot constant and considered as anadditional dependent variable. Because of the Earth'srotation effects, the air massflow to the left of the ridge and that to the rightof the ridge differ considerably intheir features. The fact that the characteristictransverse linear scale of the problem(the generalized Rossby radius of deformation) issmall compared with thelongitudinal scale permits making simplificationsthat result in a semi-geostrophicmodel of the boundary-layer type. Then the problemcan be reduced to an ordinarydifferential equation, which admits a closed-formsolution. Analysis of the solutionenables one to deduce some general features ofthe process under investigation suchas, for example, orographic front formation,a transition from sub-critical to super-criticalwind and others.  相似文献   

Labile barite contents and dissolved barium concentrations on Blake Ridge: New perspectives on barium cycling above gas hydrate systems   总被引：1，自引：0，他引：1  

G.T. Snyder  G.R. Dickens  D.G. Castellini 《Journal of Geochemical Exploration》2007,95(1-3):48

Blake Ridge hosts an extensive gas hydrate system where escaping CH₄ is consumed through anaerobic oxidation of methane (AOM) at a sulfate–methane transition (SMT) in shallow sediment. Previous geochemical work on ridge crest sediment has documented Ba fronts above the SMT, and has suggested that these horizons can be used to constrain the evolution of the SMT and AOM over time. We expand on this concept and further test it by determining the labile Ba contents of sediment and the dissolved Ba²⁺ concentrations of pore waters at four ODP sites on Blake Ridge (on the crest at Sites 994, 995 and 997, and on the southern flank at Site 1059). Labile Ba contents are fairly low at all four sites (0.44 and 1.32 mmol/kg), except within 3 m above the SMT at Sites 994, 995 and 997, where they typically exceed 1.24 mmol/kg and can reach 11.3 mmol/kg. These Ba fronts have a diagenetic origin, and SEM analyses show them to be composed of microcrystalline barite. Site 1059 lacks a prominent Ba front. The lowest labile Ba contents generally underlie the Ba fronts and correlate to the base of the SMT. Dissolved Ba²⁺ concentrations are low (< 1–4 μM) from the seafloor to within 2 m above the main Ba front. Below this depth, they rapidly increase at Sites 994, 995, and 1059, reaching peak concentrations (to 57 μM) at the base of the SMT. By contrast, a rapid rise in dissolved Ba²⁺ is not observed at Site 997. Dissolved Ba²⁺ concentrations are only moderately high (10–25 μM) below the SMT at all four sites. Collectively, this information supports a diagenetic model where barite passing into the SMT dissolves, and some of the dissolved Ba²⁺ then migrates up to form an authigenic barite peak. The contrasting signatures at the different sites indicate non-steady-state differences in the overall process. The size of the peaks on the crest of Blake Ridge necessitates that the recycling of Ba across the SMT has been operating at the current sub-bottom depths for > 100 kyr. Thus, CH₄ escaping through the AOM has likely been fairly constant over this time. It is possible that the SMT is currently rising toward the seafloor at Site 1059.  相似文献   

Evidences linking ENSO and coral growth in the Southwestern-South Atlantic     

H. Evangelista  D. Godiva  A. Sifeddine  Z. M. A. N. Leão  N. R. Rigozo  B. Segal  T. Ambrizzi  M. Kampel  R. K. P. Kikuchi  F. Le Cornec 《Climate Dynamics》2007,29(7-8):869-880

Physical and biological changes in the marine environment, induced by oceanic-atmospheric processes, can be imprinted in massive coral skeletons. Herein, we present an evidence of potential El Niño impacts at the Southwestern South Atlantic Ocean (SWSA) inferred from the sclerochronology of the reef coral Favia leptophylla. The application of spectral analysis (wavelet decomposition and the iterative regression) to coral growth length and to meteorological-oceanographic parameters (air temperature, sea surface temperature and precipitation) as well as to Southern Oscillation Index (SOI) and solar irradiation indicated a major significant inverse relationship between SOI and coral growth length at the 4–8 years frequency band. We propose here that coral growth length from the SWSA could be affected by El Niño Southern Oscillation (ENSO) events through an “atmospheric bridge”, in contrast to its direct effect at the Pacific Ocean, related to the increase in sea surface temperature.  相似文献   

Acoustic study of the Rio de la Plata estuarine front   总被引：1，自引：0，他引：1  

Cabreira  A.G.; Madirolas  A.; Alvarez Colombo  G.; Acha  E.M.; Mianzan  H.W. 《ICES Journal of Marine Science》2006,63(9):1718-1725

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Trace metal fronts in Scottish coastal waters     

P. W. Balls 《Estuarine, Coastal and Shelf Science》1985,20(6):717-728

Dissolved cadmium and copper concentrations have been determined in 76 surface water samples in coastal and ocean waters around Scotland by anodic stripping voltammetry (ASV). A trace metal/salinity ‘front’ is observed to the west, north and north-east of Scotland separating high salinity ocean water (>35 × 10⁻³) with low concentrations of dissolved Cd and Cu from lower salinity (<35 × 10⁻³) coastal water containing higher concentrations of Cd and Cu. Mean Cd concentrations in ocean and coastal waters are 7 ng dm⁻³ (0·06 n ) and 11 ng dm⁻³ (0·10 n ) respectively; for Cu the respective levels are 60 ng dm⁻³ (0·95 n ) and 170 ng dm⁻³ (2·68 n ). The observed distribution is attributed principally to freshwater runoff and the advection of contaminated Irish Sea water into the study area.  相似文献   

Spring phytoplankton bloom in the fronts of the East China Sea   总被引：2，自引：0，他引：2  

SeungHyun Son  Sinjae Yoo  Jae-Hoon Noh 《Ocean Science Journal》2006,41(3):181-189

Frontal areas between warm and saline waters of the Kuroshio currents and colder and diluted waters of the East China Sea (ECS) influenced by the Changjiang River were identified from the satellite thermal imagery and hydrological data obtained from the Coastal Ocean Process Experiment (COPEX) cruise during the period between March 1^st and 10^th, 1997. High chlorophyll concentrations appeared in the fronts of the East China Seas with the highest chlorophyll-a concentration in the southwestern area of Jeju Island (~2.9 mg/m³) and the eastern area of the Changjiang River Mouth (~2.8 mg/m³). Vertical structures of temperature, salinity and density were similar, showing the fronts between ECS and Kuroshio waters. The water column was well mixed in the shelf waters and was stratified around the fronts. It is inferred that the optimal condition for light utilization and nutrients induced both from the coastal and deep waters enhances the high phytoplankton productivity in the fronts of the ECS. In addition, the high chlorophyll-a in the fronts seems to have been associated with the water column stability as well.  相似文献   

渤海的潮混合特征及潮汐锋现象   总被引：9，自引：3，他引：9  

赵保仁  曹德明  李徽翡  王其茂 《海洋学报》2001,23(4):113-118

人们对黄海的潮汐锋现象已有一些报道和研究[1～4],但对渤海的潮汐锋现象却没有进行过认真的分析和讨论,迄今只有赵保仁[1]在讨论黄海的潮汐锋时,指出过渤海海峡的潮汐锋现象;而黄大吉等[5]在数值计算渤海的温度变化时也指出在渤海内部存在着潮汐锋现象,但却没有进行深入的分析和给出任何实测证据.本文试图根据方国洪和曹德明最近在渤海取得的潮汐潮流数值计算结果1),计算由Simpson等[6]提出的陆架海的潮混合层化参量,来讨论渤海的潮混合特征;并进一步利用实测水文资料和海面温度的卫星遥感图像来说明渤海潮汐锋的分布和变化特征.  相似文献