海洋环流与波动重点实验室知识库

  能量串级的提出至今已有80多年，虽然发展时间较短，但却为我们研究海洋动力学提供了全新的视角。一方面理论发展是不断向前的，另一方面海洋的测量越来越多元化，精度也越来越高，再加上数值模拟的帮助，海洋动力机制的研究也越来越深入。目前地转平衡的中尺度涡和非地转平衡的小尺度湍流已经得到了很好的研究，但是他们之间的联系尚不清楚，其在垂直维度的关联更是研究甚少。本文研究发现，惯性重力波螺旋在地转的中尺度涡和小尺度湍流之间的能量串级和拟能串级中起到重要的作用，是通过减小能量耗散来维持中尺度涡长寿命的重要原因。

  本文采用卫星高度计数据识别墨西哥湾流和加利福尼亚流中的中尺度涡，采用穿过涡心的ADCP数据来进行波涡分解，即将其能量谱分解为惯性重力波的部分和地转流的部分，然后进行能量串级和拟能串级的计算。计算结果表明带有惯性重力波螺旋的中尺度涡内部形成了半循环能量圈：中尺度气旋涡就像一个垂直中心收缩两端膨胀的的变形圆柱体，同时其涡心处为拉伸状态的的惯性重力波螺旋，其能量在垂直中心处从中尺度涡的尺度正向串级到惯性重力波螺旋内的小尺度，再由惯性重力波螺旋的中心传递到其两端，然后在两端从惯性重力波螺旋内的小尺度逆向串级到了中尺度涡的尺度，从而形成了中尺度气旋涡的半循环能量圈；中尺度反气旋涡就像一个垂直中心膨胀两端收缩的的变形圆柱体，同时其涡心处为压缩状态的的惯性重力波螺旋，其能量在两端从中尺度涡的尺度正向串级到惯性重力波螺旋内的小尺度，再由惯性重力波螺旋的两端传递到其中心，然后在垂直中心处从惯性重力波螺旋内的小尺度逆向串级到了中尺度涡的尺度，从而形成了中尺度反气旋涡的半循环能量圈。当连接不同涡中的惯性重力波螺旋便形成了全循环能量圈，就如同人体的毛细血管交换能量一样。原本正向串级到小尺度的能量是要耗散掉的，但是由于惯性重力波螺旋的作用使一部分小尺度的能量又在另一深度处逆向串级到大的尺度，从而减小了能量耗散，这也是中尺度涡有更长寿命的重要原因。在中尺度气旋涡中，由于位涡守恒，拉伸的惯性重力波螺旋提供了涡度的源，在惯性重力波螺旋内部拟能从惯性重力波螺旋的尺度正向串级到小尺度，在惯性重力波螺旋外部拟能从惯性重力波螺旋的尺度逆向串级到大的尺度，逆向的拟能串级减少了耗散。在中尺度反气旋涡中，由于位涡守恒，压缩的惯性重力波螺旋提供了涡度的汇，在惯性重力波螺旋内部拟能从小尺度逆向串级到惯性重力波螺旋的尺度，逆向的拟能串级减少了耗散，在惯性重力波螺旋外部拟能从大的尺度正向串级到惯性重力波螺旋的尺度。同时由于中尺度涡中惯性重力波螺旋的作用，在较小的尺度上能量谱的坡度变缓，其在较大尺度的幂次斜率为（-3，-2），其在较小尺度的幂次斜率为-1。而拟能谱大致比能量谱大两个量级，拟能谱在较大尺度的幂次斜率为（-1，0），在较小尺度的幂次斜率为1。

  本文采用LLC4320 MITgcm 模式数据对德雷克海峡地区的的南极绕极流进行研究。探究了亚中尺度指标SMI与混合层深度MLD、变形应变率MSR以及锋生指标F的相关性及其空间分布，并进一步探究了亚中尺度指标SMI分别与正压能量BT和斜压能量BC的相关性及其空间分布。本文根据不同深度处的位温识别了亚南极锋（SAF）、极锋（PF）和南绕极流锋（SACCF），按照混合层深度的变化趋势划分了四个时间段，在不同的时间段里南极绕极流、中尺度涡、水道突变起伏的地形以及南北岸边逐渐变浅的海底地形对各个物理量在空间分布上都产生了不同的影响。亚中尺度过程的研究对进一步探究海洋动力学有重要意义。

    The energy cascade has been proposed for more than 80 years. Although its development time is relatively short, it provides a new perspective for us to study ocean dynamics. On the one hand, the theoretical development is constantly moving forward. On the other hand, the marine measurement is becoming more and more diversified, and the accuracy is getting higher and higher. Coupled with the help of numerical simulation, the research on ocean dynamic mechanism is becoming more and more in-depth. Although geostrophically balanced mesoscale vortices and unbalanced small-scale turbulence have been well studied, the link between them is not entirely clear, especially the relationship between them in the vertical dimension is rarely studied. Our study finds that the inertia-gravity wave (IGW) spiral plays an important role in the energy and enstrophy cascades between the geostrophic vortex and the small-scale turbulence, which is an important reason to maintain the long life of the mesoscale vortex by reducing energy dissipation.

    The satellite altimeter data are used to identify the mesoscale vortices in the California current and the Gulf Stream, and the ADCP data passing through the vortex center is used to calculate the wave-vortex decomposition of the energy spectrum, which are decomposed into the inertia-gravity wave component and the geostrophic flow component with depth. We also calculate the energy cascades and enstrophy cascades. Our study show that a vertical semi-circulating cycle of the energy cascades in the mesoscale vortex with IGW spirals. A cyclonic vortex is just like a deformed cylinder that shrinks in the vertical centre and expands at both ends with stretching IGW spirals in its vortex center. Its energy cascades forward from the cyclonic vortex scale to small scales in the IGW spiral in the vertical centre, transfers from the center of the IGW spiral to its two ends, and then inversely cascades from the small scales in the IGW spiral to the cyclonic vortex scale at both ends, thus forming the vertical semi-circulating cycle of the energy cascades in the mesoscale cyclonic vortex. An anticyclonic vortex is just like a deformed cylinder that expands in the vertical centre and shrinks at both ends with compression IGW spirals in its vortex center. The energy cascades forward from the anticyclonic vortex scale to small scales in the IGW spiral at both ends, transfers from the two ends of the IGW spiral to its center, and then inversely cascades from the small scales in the IGW spiral to the anticyclonic vortex scale in the vertical centre, thus forming the vertical semi-circulating cycle of the energy cascades in the mesoscale anticyclonic vortex. A vertical full-circulating cycle is formed by connecting every IGW spiral in different geostrophic vortices, similar to the energy exchange in the capillaries of the human body. Originally, the energy from forward cascade to small scale should be dissipated, but due to the role of IGW spiral, some small-scale energy is inversely cascaded to large scales at another depth, thereby reducing the energy dissipation, which is also an important reason for the longer life of mesoscale vortex. In mesoscale cyclonic vortices, due to the conservation of potential vorticity, the stretched IGW spiral provides a source of vorticity; inside the IGW spiral, the enstrophy cascades forwardly from the IGW spiral scale to the small scales; outside the IGW spiral, the enstrophy cascades reversely from the IGW spiral scale to the large scales, which reduces the dissipation. In mesoscale anticyclonic vortices, due to the conservation of potential vorticity, the stretched IGW spiral provides a sink of vorticity; inside the IGW spiral, the enstrophy cascades reversely from the small scales to the IGW spiral scale, which reduces the dissipation; outside the IGW spiral, the enstrophy cascades forwardly from the large scales to the IGW spiral scale. Due to the role of IGW spiral in the mesoscale vortex, the slope of the energy spectrum at smaller scale becomes flatter at smaller scale than that at larger scales. Its power-law slope is (- 3, - 2) at the larger scales and - 1 at the smaller scales. The power-law slope of the enstrophy spectrum is about two orders of magnitude larger than that of the energy spectrum. The power-law slope of the enstrophy spectrum is (- 1, 0) at the larger scales and 1 at the smaller scales.

    The LLC4320 MITgcm model data are used to study the Antarctic Circumpolar Current in the Drake Passage. The correlation and spatial distribution of submesoscale index SMI with mixed layer depth MLD, deformation strain rate MSR and frontogenesis index F are explored, and the correlation and spatial distribution of submesoscale index SMI with barotropic energy BT and baroclinic energy BC are further explored. In this paper, the subantarctic front (SAF), polar front (PF) and southern ACC front (SACCF) are identified according to the potential temperature at different depths. According to the variation trend of mixing layer depth, four time periods are divided. In different time periods, the Antarctic Circumpolar Current, mesoscale vortex, The drastically changing seabed topography and the gradually shallowing seabed topography of the north and south banks have different effects on the spatial distribution of each physical quantity. The study of submesoscale processes is of great significance to further explore ocean dynamics.

第1章 绪论... 1

1.1 研究背景和意义... 1

1.2 研究现状和研究进展... 2

1.2.1 能量串级的研究现状... 2

1.2.2 惯性重力波的研究现状... 3

1.2.3 能量串级和耗散的关系... 4

1.2.4 亚中尺度的研究现状... 5

1.3 主要内容及章节安排... 6

第2章 能量串级的方法理论... 8

2.1 能量谱波涡分解... 8

2.2 中尺度涡中慢变的惯性重力波螺旋... 9

2.3 能量通量谱和拟能通量谱... 11

2.3.1 能量通量谱... 11

2.3.2 拟能通量谱... 12

2.4 中尺度涡中的惯性重力波螺旋对能量串级和拟能串级的引擎功能... 13

2.5 本章小结... 13

第3章 带有慢变惯性重力波螺旋的中尺度涡能量串级和拟能串级... 15

3.1 数据资料... 15

3.1.1 卫星观测数据... 15

3.1.2 ADCP数据... 15

3.2 中尺度涡速度场及其内部慢变惯性重力波螺旋... 16

3.3 能量、拟能以及波涡分解... 20

3.3.1 能量和拟能... 20

3.3.2 能量谱的波涡分解... 23

3.4 能量串级和拟能串级... 28

3.5 中尺度涡中能量和拟能的转换... 36

3.6 本章小结... 39

第4章 南极绕极流的亚中尺度过程... 43

4.1 数据资料和研究方法... 43

4.1.1 模式数据... 43

4.1.2 锋面判别及德雷克海峡海底地形... 43

4.1.3 亚中尺度指标... 47

4.1.4 能量过程分析方法... 48

4.2 德雷克海峡亚中尺度空间特征及能量分析... 49

4.2.1 德雷克海峡亚中尺度空间特征... 49

4.2.2 德雷克海峡亚中尺度能量过程... 77

4.3 本章小结... 90

第5章 全文总结与展望... 93

5.1 本文的主要结论... 93

5.2 本文的创新点... 94

5.3 工作展望... 94

参考文献... 96

致 谢... 105

作者简历及攻读学位期间发表的学术论文与研究成果... 107