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1.
基于高精度海洋动力模型FVCOM (finite-volume community ocean model), 模拟分析了1999—2010年珠江口羽状流的季节和年际变化规律, 并结合经验正交函数(empirical orthogonal function, EOF)分析探讨了影响珠江口羽状流扩展变化的主要动力因子。采用模拟时段内的现场观测数据对多年模拟结果进行验证, 结果表明模型具有较高的精度, 能够较好地模拟珠江口羽状流的扩展变化规律。模拟结果显示, 珠江口羽状流存在显著的季节变化。夏季, 受大径流和西南风的影响, 羽状流的扩展呈现双向特征, 即粤西沿岸扩展和粤东离岸扩展同时存在, 扩展范围最大; 冬季, 径流衰减为最小值, 风场转变为强烈的东北风, 羽状流被紧紧挤压在西岸, 形成狭窄的条带状, 扩展范围最小; 春、秋两季属于过渡季节, 羽状流扩展情况类似, 均表现为沿岸向粤西扩展。年际变化层面, 夏季羽状流的年际变化最为显著, 呈现粤东扩展占优型、近似对称型和粤西扩展占优型三种形态; 春季羽状流的年际变化次之, 羽状流的差异主要体现在珠江口和粤西海域; 秋、冬两季羽状流的年际变化较小, 尤以冬季最小。EOF分析的第一模态可以解释整体变化的91.2%, 反映了径流量对珠江口羽状流的影响; 第二模态可以解释整体变化的4.1%, 反映了盛行风对珠江口羽状流的影响。 相似文献
2.
深海采矿尾矿排放产生的细颗粒羽状流会对海底生态环境造成影响,预测尾矿排放羽状流行为及其对环境影响具有工程意义。基于欧拉多相流方法,采用欧拉双流体模型对深海采矿细颗粒羽状流开展数值模拟研究,分析近海底排放的羽状流演化和发展过程,探究羽状流初始排放质量浓度、排放速度对羽状流扩散过程的影响。结果表明：初始排放条件对羽状流演化性质有重要影响。主射流区被稀释的程度随着初始入射速度的增大而减小,随着入射质量浓度的增大而增大;初始羽状流入射速度和质量浓度越大,撞击海底后的水平方向流动速度越快,影响区域越广;水平速度的峰值随着初始入射速度的增大呈对数增长;当初始质量浓度和速度高于50 g/L和 0.5 m/s 时可能会导致颗粒在海底撞击点附近堆积成坡状,影响底流的后续发展。研究结果可以为深海采矿尾矿排放参数选择提供参考。 相似文献
3.
冷泉活动区气泡羽状流数值模拟的进一步研究 总被引：1，自引：1，他引：0
以南海气泡羽状流赋存特征为参考,本文继续研究冷泉活动区气泡羽状流的地震响应。为使羽状流建模方案更合理,根据水中气泡在上升过程时其半径的变化情况,修改原建模方案,重新建立了羽状流水体模型。通过正演模拟得到了羽状流炮集地震记录,单炮记录上显示出明显的散射波场特征和模型的周期特点。通过叠前深度偏移处理炮集地震记录,得到边界收敛效果较好的成像剖面,且成像精度较高。以上研究又一次奠定了羽状流地震响应进一步研究的基础,也逐步探索出更适合羽状流地震资料的处理方法,为识别羽状流提供了理论指导。 相似文献
4.
热液羽状流是海底热液活动的重要标志，海底多金属硫化物是热液活动的产物。现阶段洋中脊多金属硫化物勘探工作的第一步是开展热液羽状流的近底探测；综合各类异常信息，实现从发现热液活动喷口到发现矿床的突破。本文以热液羽状流为研究对象，从羽状流的近底探测、扩散机制和分布特征3个方面，概述了最新的研究进展和有待完善的方面，阐述了羽状流在洋中脊多金属硫化物找矿中的指示作用，最后总结性地指出时空连续性、参数多元化将是热液探测的发展趋势，有助于提升对热液羽状流分布特征的认识，将为热液区分布模式的研究提供更加精细的探测资料。 相似文献
5.
一个概化的潮汐河口羽状流动力学的初步研究 总被引：1，自引：0，他引：1
基于区域陆架海水动力-生态耦合模型(COHERENS)中的三维水动力模型,对一个概化的潮汐河口羽状流动力学进行了初步研究。在均一水深和无风的理想条件下,模拟得到了一个潮周期内概化的潮汐河口表层水体:a)羽状流流场和盐度场的平面分布;b)3种不同河流径流量作用下的羽状流流场和盐度场的平面分布;c)4种不同底床粗糙长度下的羽状流流场和盐度场的平面分布。结果分析表明:a)羽状流的长度在潮汐的作用下递增,而其最大宽度近似呈周期性的变化;b)羽状流的长度和最大宽度都随着河流径流量的增大而分别变长和变宽;c)羽状流的长度和最大宽度都随底床粗糙长度的增大而变小;d)无潮情况下羽状流的凸起明显并存在沿岸流,然而在有潮情况下凸起不明显且无沿岸流;e)水平扩散可能限制了沿岸羽状流的发展。 相似文献
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2002年黄河实施调水调沙以来,黄河入海泥沙普遍以异轻羽状流的形式在河口附近的有限区域内堆积下来。采用2011年、2012年以及2013年调水调沙期间3期静止轨道海洋水色卫星(GOCI)数据对黄河口附近海域进行悬浮物浓度反演,提取了黄河口羽状流的逐时变化信息;通过黄河口水动力数值模拟以及风场、潮汐等实测数据分析,阐明了羽状流逐时变化的驱动机制。研究结果表明:黄河调水调沙前后黄河口羽状流表现出单向变化和往复变化两种不同的变化过程;而悬浮物浓度的逐时变化显示:河口附近不同站位的悬浮物浓度逐时变化过程差异较大,同一站位的悬浮物浓度可在1小时之内升高或降低约100mg/L。单向变化型羽状流主要受单向潮流的控制,且GOCI观测时段位于一个落潮或者涨潮过程,河流动力较弱;往复变化型羽状流受涨、落潮往复潮流的控制,涨、落潮流向的转换驱使羽状流向相反的方向运动,而且羽状流位于潮流切变带以内,切变锋对羽状流的形态、分布范围具有明显的切变效应。 相似文献
8.
利用2016年在南海西北部陆坡琼东南海域采集的多波束水体数据,发现了海底气体渗漏至海水中形成的羽状流。在多波束数据上, 羽状流成火焰状,直径大约为30~50 m,从1 380多米的海底延伸至大约650 m的深度,高度超过700 m。在经过羽状流的浅剖剖面上,存在显示浅层气存在的声学空白区域,并识别出断裂和裂隙区域,但在水体中并无明显的异常。这可能是由于浅剖数据的分辨率不够未能捕捉到水体异常,或者气体渗漏具有间歇性。该海域存在明显的似海底反射显示,气体渗漏可能与水合物系统之间存在复杂的相互作用。由于缺乏经过羽状流的多道地震数据,难以对羽状流的形成机制进行进一步的推测。南海北部陆坡羽状流的发现对于理解被动大陆边缘的甲烷渗漏机制、水合物的形成与分解具有重要的意义。 相似文献
9.
羽状流的近场扩散角作为河口动力学的关键参数,对河流入海物质的输运扩散过程有重要影响,而在真实环境中由于受到复杂因素的影响,羽状流扩散角存在着显著的变化。数据挖掘技术尽管在地学数据的应用上尚处于探索阶段,但研究这一问题提供了一种有效途径。本文基于马格达莱纳河羽状流近场扩散角及周边环境数据,利用多重数据挖掘算法开展数据分析和评估,最终建立了羽状流扩散模型,对其影响因素和时间序列开展研究。结果表明,数据挖掘算法能够有效指示环境因素的贡献值而不受量纲、极值的影响,从而为进一步探究河口羽状流控制因素提供参考。受数据量和数据精度的影响,随机森林算法得到的变量分析结果与实际情况更为相似,数据集特征与数据量之间的博弈是造成模型结果差异的主要原因。根据数据挖掘算法结果,可以在马格达莱纳河河口建立羽状流扩散角模型,并分析其随环境参数和时间变化的趋势。模型结果显示,对马格达莱纳河而言,环境因素与羽状流扩散角均存在负相关关系,河流的指向方向为最主要影响因素,其次为风速,因此在开展进一步分析时可以针对环境因素添加不同权重以期获得更真实的结果。随时间增长,羽状流扩散角将进一步收紧,可能会引起河口的通道化。 相似文献
10.
《海洋地质与第四纪地质》2017,(5)
羽状流对天然气水合物的识别起到了间接指示作用,为研究冷泉活动区气泡羽状流产生的地震响应,需建立符合实际羽状流特征的模型。为此,参考实际羽状流赋存状态,结合含气泡水体特征,在已建立模型基础上,从羽状流气泡的垂直运移规律、分布特点及羽状流外观特征上对模型进行了改进,先后获得3个羽状流模型,最后的模型Ⅲ更接近实际羽状流赋存特征。通过与实际羽状流的对比,讨论分析了模型Ⅲ的合理性,并得出结论:所建模型体现了实际羽状流气泡的本质特征,并包含了更为复杂的气泡含量变化,可用于进一步深入研究羽状流地震响应特征,也为气泡羽状流的地震识别及天然气水合物的相关研究提供了较好的数值模型。 相似文献
11.
By E. DARELIUS L. H. SMEDSRUD S. ØSTERHUS A. FOLDVIK T. GAMMELSRØD 《地球，A辑:动力气象学与海洋学》2009,61(3):446-464
Properties of the dense ice shelf water plume emerging from the Filchner Depression in the southwestern Weddell Sea are described, using available current meter records and CTD stations. A mean hydrography, based on more than 300 CTD stations gathered over 25 yr points to a cold, relatively thin and vertically well-defined plume east of the two ridges cross-cutting the continental slope about 60 km from the Filchner sill, whereas the dense bottom layer is warmer, more stratified and much thicker west of these ridges. The data partly confirm the three major pathways suggested earlier and agree with recent theories on topographic steering by submarine ridges. A surprisingly high mesoscale variability in the overflow region is documented and discussed. The variability is to a large extent due to three distinct oscillations (with periods of about 35 h, 3 and 6 d) seen in both temperature and velocity records on the slope. The oscillations are episodic, barotropic and have a horizontal scale of ∼20–40 km across the slope. They are partly geographically separated, with the longer period being stronger on the lower part of the slope and the shorter on the upper part of the slope. Energy levels are lower west of the ridges, and in the Filchner Depression. The observations are discussed in relation to existing theories on eddies, commonly generated in plumes, and continental shelf waves. 相似文献
12.
MPAS-Ocean is used to simulate an idealized, density-driven overflow using the dynamics of overflow mixing and entrainment (DOME) setup. Numerical simulations are carried out using three of the vertical coordinate types available in MPAS-Ocean, including z-star with partial bottom cells, z-star with full cells, and sigma coordinates. The results are first benchmarked against other models, including the MITgcm’s z-coordinate model and HIM’s isopycnal coordinate model, which are used to set the base case used for this work. A full parameter study is presented that looks at how sensitive overflow simulations are to vertical grid type, resolution, and viscosity. Horizontal resolutions with 50 km grid cells are under-resolved and produce poor results, regardless of other parameter settings. Vertical grids ranging in thickness from 15 m to 120 m were tested. A horizontal resolution of 10 km and a vertical resolution of 60 m are sufficient to resolve the mesoscale dynamics of the DOME configuration, which mimics real-world overflow parameters. Mixing and final buoyancy are least sensitive to horizontal viscosity, but strongly sensitive to vertical viscosity. This suggests that vertical viscosity could be adjusted in overflow water formation regions to influence mixing and product water characteristics. Lastly, the study shows that sigma coordinates produce much less mixing than z-type coordinates, resulting in heavier plumes that go further down slope. Sigma coordinates are less sensitive to changes in resolution but as sensitive to vertical viscosity compared to z-coordinates. 相似文献
13.
In the summer seasons of 2004–2007, the intensive runoff (cascading) of the Antarctic shelf water (ASW) down the shelf and
continental slope was revealed thanks to the recording of numerous thermohaline profiles across the shelf and continental
slope of the Commonwealth Sea and Prydz Bay. The quickly executed profiles (4–10 h) with submesoscale resolution (near the
shelf’s edge, the scale was even eddy-determinative, i.e., within 1.9–5.6 km), in combination with the fine-structure sounding
and fine vertical resolution of the near-bottom boundary layer, provided a qualitatively new level of understanding the natural
data. The detailed analysis of the temperature, salinity, and density patterns revealed the regularities and peculiarities
of the ASW shelf and slope cascading. The intensive ASW cascading near the shelf break and lower part of the slope can be
forced (appearing as discrete frontal meanders) or free (appearing as discrete plumes) and often has a wave-eddy character.
The field observational data confirmed the obtained representative estimates of the elements of the ASW slope cascading. The
basic area of the ASW formation is near the Amery Shelf Ice, from where the ASW spreads to the northwest, goes around the
Fram Bank, and flows down the continental slope. The evaluative contribution of the ASW slope cascading to the ventilation
of the deep and slope water of the Southern Ocean (near the shelf break 70 km long where the ASW cascading was observed) is
Q
K
= 0.04–0.24 Sv, which agrees well with the analogous estimates obtained in other regions of the Antarctic. 相似文献
14.
G. A. Platov 《Izvestiya Atmospheric and Oceanic Physics》2011,47(3):362-376
In this study the capability of numerical models to transport anomalously dense bottom waters from the areas of their generation on the shelf to deepwater areas is considered. These numerical models have a number of mechanisms that are favorable for this transport, but unrelated directly with the real physics of that motion. A more accurate account of the resupply of oceanic deep waters requires either a very fine resolution for the numerical model or an efficient parametrization. Two such parametrizations are proposed in this study. The first is based on amplified lateral diffusion exchange if slope instability exists. The second is related to an additional procedure allowing dense waters to leak under waters of lesser density along a shelf slope with their displacement to higher layers. The first parametrization is shown to be less efficient because it leads to a significant interaction between anomaly waters and ambient waters and to a quick loss of their original features. The second procedure is more preferable because it leads to a significant resupply of dense deep waters at the expense of dense waters generated at a distance significantly far from the shelf break. With the help of the given parametrization, during a numerical experiment these waters can be transported considerable distances away from their place of generation to the shelf boundary and deepwater areas of the ocean with a slight change in their original density characteristics. 相似文献
15.
L. D. Wright Z. -S. Yang B. D. Bornhold G. H. Keller D. B. Prior W. J. Wiseman Jr. 《Geo-Marine Letters》1986,6(2):97-105
The Huanghe (Yellow River) discharges extremely high suspended sediment concentrations (25 to 220 g/l) which favor sustained hyperpycnal plumes (underflows). Observations of weakly hyperpycnal unchannelized plumes and indirect evidence of strongly hyperpycnal channelized underflows over the delta front indicate the importance of these modes of sediment dispersal. The weakly hyperpycnal plumes occupy the entire water column over the shallow (<5 m) delta top. From a pronounced front near the break in slope at about 5 m depth, they descend over the delta-front slope as wide-spread underflows. Evidence of strongly hyperpycnal underflows was shown from subaqueous valleys partly filled with low-density mud. 相似文献
16.
A two-dimensional non-hydrostatic ocean model and a hydrostatic version of the same model are used to simulate convective adjustment, without the use of an instantaneous adjustment parameterization. The model geometry is a domain on the vertical plane of width 40 km and depth 500 m. Model results for four cases are examined: hydrostatic and non-hydrostatic, at 0.1 and 1 km spatial resolution. The convectively adjusted stable state obtained in all four cases are qualitatively similar; thus the hydrostatic approximation does not eliminate convective adjustment. The details of the simulated convective plumes depend on resolution and whether the hydrostatic approximation is made. The adjusted state has significant stratification which cannot be captured by the conventional instantaneous adjustment or diffusion-based parameterizations. We also compare the results to the case when an instantaneous adjustment parameterization is used. 相似文献
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In OMEX-II-II, 9 cruises gathered optical data, principally by transmissometer. The distribution of optical turbidity caused by concentration of particulate matter (PMC) in the water column over the northern Iberian margin shows several features related to hydrography. It is concluded that a signal of PMC seen in Mediterranean Water (MW) found north of 42°N is not carried from its source at the Gibraltar Sill and Gulf of Cadiz because it is shown, using intermediate stations, that this turbid plume decays, mainly by fall out but also partly by mixing, to very low levels around southern Portugal. PMC maxima sometimes seen in MW on the northern Iberian margin are thus most likely to result from intermittent local resuspension by MW interacting with slope sediments. The highest turbidity is found over the upper slope and is the result of (i) shelf edge resuspension and off-shelf flow of turbid plumes, mainly between 100 and 300 m depth, and (ii) resuspension under the slope current aided by internal waves, in the depth range 500–800 m where the density gradient between ENACW and MW is maximal. Below the MW, flows are generally slow, and turbidity is low. The bottom nepheloid layer in deep water is also weak with PMC values <100 mg m-3. The focus of resuspension activity on the upper slope means that the region is an efficient exporter to the ocean of sediment that either escapes from the shelf or sinks to the bed from surface production. This accounts for upper slope sediments recorded in other studies as sandy or in places as rocky bottom. 相似文献
19.
P. N. Golovin 《Oceanology》2007,47(1):42-50
Comprehensive field observations of hydrological processes in the region of the continental slope of Severnaya Zemlya in the Laptev Sea allowed us to reveal descending dense (cold) shelf water over the slope (cascading) and to determine the spatiotemporal variability of the cascading [2]. The observations represented a series of polygon surveys in the autumn-winter-spring period. The estimates of the characteristics of the slope convection of the shelf water (cascading) were based on the results of laboratory and theoretical studies of the descending of the dense water over a sloping bottom in a rotating fluid with sources of different geometry. It was shown that the cascading of dense shelf water over the continental slope mainly corresponds to a smooth (geostrophic) regime. An analysis of some thermohaline and density sections indicates, however, the possibility of the development of a wave-eddy regime of cascading and/or generation of fast gravity waves in the upper part of the continental slope. The most representative estimation of the contribution of the cascading of dense shelf water on the northern continental slope of Severnaya Zemlya to the ventilation of the intermediate waters in the Nansen Basin for five winter months is ≈0.0614 Sv. 相似文献