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题名: 东海黑潮陆架坡折锋不稳定性研究
作者: 张艳华
学位类别: 博士
答辩日期: 2017-07-25
授予单位: 中国科学院大学
授予地点: 北京
导师: 王凯
关键词: 东海黑潮+坡折锋+不稳定性+谱方法
学科分类: 地球科学::海洋科学 ; 地球科学::海洋科学::海洋物理学
学位专业: 理学博士
中文摘要:  现场观测资料和卫星遥感观测表明东海黑潮锋面常出现摆动弯曲。锋区是物质性质急剧变化的区域,它们会对流场结构、热量交换、物质输运、海气相互作用、渔业生产等产生重要影响。因此,研究黑潮摆动弯曲和黑潮陆架坡折锋的不稳定性有重要的理论价值和实际应用意义。
本文建立了一个利用谱方法,求解描述陆架坡折锋的简化线性模型,此模型曾成功的应用于湾流弯曲变化问题的讨论。湾流和黑潮作为大西洋和太平洋中的强劲西边界流,两者性质多有相似之处,但地形、海洋环境要素等有差异,湾流最不稳定波的相速度几乎是黑潮的两倍,最不稳定波的周期为黑潮的一半。为了研究这些差别的原因,探讨东海黑潮坡折锋的稳定性,构建刻画黑潮形态的流速函数和地形函数,通过数值实验考察流速形态参数、地形参数的影响,得到以下结果:
   一,流速形态参数的影响。东海黑潮流速形态多样,本文构造了三种速度流形的解析函数。从流速大小和流核位置两方面,考察对坡折锋不稳定性的影响。流速越大,不稳定发生范围越广。当流核远离陆架时,能量转化率与流核位于陆坡处时相近。
二,地形参数的影响。东海黑潮段的海底地形复杂,本文构造了三个理想的地形函数,分别对应于底部平坦、有海山和有海沟的情形。从陆架深度、陆架宽度、陆坡陡度的变化这几方面,考察对陆架坡折锋不稳定性的影响。结果表明:陆架越深,能量转化越活跃,坡折锋越不稳定;陆架宽度越大,平均动能转化为涡动能越少,而涡势能转化为涡动能越多。
三,比较计算平底地形和理想地形的能量分布和能量结构,发现平底地形时,雷诺应力项和水平热通量项的比值约为3:1;理想地形时,平均位能通过涡势能向涡动能贡献了约80%的能量。并且在平底和理想地形的情形,主要是平均位能向涡动能转化。
本文通过数值计算模拟了东海黑潮段的黑潮流态,结果显示在主流附近常伴有摆动弯曲与涡旋。主流为单核时,东海黑潮最不稳定波的周期为8天左右,波长为200 km左右,相速度约为25 km/d。在陆坡底层带有逆流的情形,东海黑潮最不稳定波的周期为11天左右,波长为180 km左右,相速度为14 km/d。
英文摘要: The field observation and a large number of satellite remote sensing images show that many eddies and meanders in the Kuroshio were observed. The frontal zone is a region of rapid change in material properties. The oceanic fronts are the most intense ocean energy from large scale to small scale in the transfer process, which is an important factor affecting the structure of the ocean flow, ocean heat exchange and mass transport and air-sea interaction. Therefore, it has important theoretical value and practical significance to study the instability of the Kuroshio meander and the Kuroshio shelf break front.
In this paper, the spectral method is used to solve the simplified linear equations of the continental shelfbrak front. This method has been used successfully to represent meanders in the Gulf Stream in the Atlantic. The Gulf Stream and the Kuroshio are strong western boundary currents. There are many similarities between the Gulf Stream and the Kuroshio. But the Gulf Stream meanders have approximately twice the phase speed and half the period of the Kuroshio meanders. To investigate the reasons for these differences, the flow and topography of the model background state were varied. The most unstable wave is found by using the high precision spectral model, and the physical properties of the most unstable wave are analyzed. The main conclusions are obtained by numerical experiments:
Firstly, the influence of the current function parameters is studied. The observation data show that the structure of the Kuroshio in the East China Sea is diversity. According to the observation data, three typical current functions of the Kuroshio current are constructed. The results show that the current velocity is greater, the range of instability will be broader. The current core is located at the shelf break of the slope, and the period of the most unstable wave is shorter, about 5 days. If the current core is far away from the shelf, the period of the most unstable wave is about 9 days.
If the core of the current away from the continental shelf, the rate of the energy conversion rate is the same to the core of the current located in the continental slope.
Secondly, the influence of topographic parameter is studied. The topography of the Kuroshio current is relatively complex. In this paper, three ideal topography function are adopted, including continental shelf, shelf slope, seamounts and oceanic trench. From the aspects of the depth of the shelf, the width of the continental shelf and the slope of the continental shelf, these factors that affect the stability of the shelf break front are investigated. The results show that the depth of the shelf is shallower and the contential shelf break front is more unstable. The shelf is wider, the conversion of the mean kinetic energy to the eddy kinetic energy is less and the conversion of the mean potential energy to the eddy kinetic energy is more.
Thirdly, the difference between having the flat bottom and the ideal bottom topography. Through the numerical calculation of energy, the spatial distribution structure of energy and the energy transfer diagram are given. In the flat bottom, the ratio between the Reynolds stress and the horizontal heat flux is about 3:1. In ideal the bottom topography, the conversion of the mean potential energy to the eddy potential energy and the conversion of the eddy potential energy to the eddy kinetic energy contribute abot 80% of the eddy energy. The conversion of the mean potential energy to the eddy potential energy is dominant.
Numerical simulation shows that the mainstream is often accompanied by eddies and meanders. The most unstable wave with the single core of the current from the model has a period of 8 days, a phase speed of 20 km/d and a wavelength of 200 km. The most unstable wave with the countercurrent in the bottom from the model has a period of 11 days, a phase speed of 14 km/d and a wavelength of 180 km.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.qdio.ac.cn/handle/337002/136920
Appears in Collections:海洋环流与波动重点实验室_学位论文

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作者单位: 中国科学院海洋研究所

Recommended Citation:
张艳华. 东海黑潮陆架坡折锋不稳定性研究[D]. 北京. 中国科学院大学. 2017.
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