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。
|其他摘要||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.
|学科领域||海洋科学 ; 海洋物理学|
|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.|