Institutional Repository of Key Laboratory of Ocean Circulation and Wave Studies, Institute of Oceanology, Chinese Academy of Sciences
|Alternative Title||Energy Transfer Characteristics of the Eddy-Mean Flow Interaction in the Kuroshio Basin, East China Sea|
|Place of Conferral||中国科学院海洋研究所|
黑潮区域存在着多空间尺度的海洋动力过程，该区域的能量源汇收支可以更准确地描述海洋能量循环和转换。在0.02-0.1cpkm的波数范围内，一维能量谱密度的斜率在-5/3和-3之间变化，这表明了台湾以东黑潮和东海黑潮区域存在能量逆向串级。根据稳态下的能量演化，该处必然存在能量源。利用24年OFES模式数据计算能量谱转移来确定能量源的位置。在海表面，动能源在小于0.02cpkm范围内主要处于23.2°-25.6°N与28°-29°N两个纬度带上，在0.02-0.1 cpkm范围内处于23.2°-25°N与26°-30°N内；有效势能在在小于0.02 cpkm范围内主要处于22°-28°N和28.6°-30°N内，在0.02-0.1 cpkm范围内处于22.6°-24.6°N、25.4°-28°N和29.2°-30°N内。在海面以下，能量源主要在400 m深度以上。风应力和密度差异分别是造成动能和有效势能源的主要原因。一旦形成能量源，为了保持稳态，将产生能量串级（通过计算能量谱通量，主要是逆向串级）。通过计算600 m处的能量通量，动能随深度从流入（汇）变为流出（源），源和汇的转换深度为380 m。然而，有效势能在整个深度上表现为源。
涡-流相互作用一直是研究人员感兴趣的问题，因为它是造成能量串级的原因之一。与之前大多数研究不同，本文主要关注于多个独立的椭圆形涡旋与黑潮相互作用过程中黑潮对于涡旋的影响。以涡旋-黑潮相互作用期间涡旋变形规律作为统计标准，选择与台湾以东黑潮相互作用的典型的涡旋。利用1993年至2018年的高度计数据，共选择处9个反气旋涡与15个气旋涡符合以上标准。气旋涡与黑潮接触面的反向速度造成了阻塞效应导致了气旋涡边缘涡动能（Eddy Kinetic Energy, EKE）分布明显不均匀，而反气旋涡则不会产生这种效应。此外，在涡旋-黑潮相互作用期间，EKE的时间变化分别提前于反气旋涡/气旋涡变形约0.55/0.27个相互作用周期。黑潮对不同极性的涡旋有不同的调制机制。通过计算能量收支，反气旋涡的EKE主要由于正压不稳定产生，而气旋涡的EKE则由正压和斜压不稳定共同产生。反气旋涡对黑潮的平流作用与黑潮对反气旋涡的平流作用是反相位的，这使反气旋涡逐渐缩小。对于气旋涡来说，它们是同相位的，最终导致气旋涡成为开口朝向黑潮的蜿蜒。
The energy transfer is a major concern in oceanic energetics, and the eddy-mean flow interaction is one of the important steps in the cross-scale energy transfer. The observations show that the mesoscale eddies generated in the inner ocean will “migrate” westward in the form similar to long Rossby waves. That results in a systematic adjustment of circulation structure and energy distribution in the ocean by transporting energy in the form of mesoscale eddies to the west. As the northward branch of the North Equatorial Current, Kuroshio is the strongest westward boundary current in the northwest Pacific region, and is also an important link between the ocean and the offshore China (including the South China Sea and East China Sea) for material and energy transfer. The frequently westward propagating eddies and the stable strong Kuroshio converge near the main Kuroshio system in the China offshore (including the Kuroshio basin east of Taiwan and the East China Sea), which gives us a natural experimental field to study the eddy-mean flow interactions. The solution of these questions will contribute greatly to the study of the multi-temporal-spatial scale variation of Kuroshio intensity, amplitude and rate of flow, and will also will also have a significant impact on the variation of the invasion pattern and water exchange between the Kuroshio downstream and the East China Sea shelf, as well as the modulation of climatic change in the coastal region of China by the oceanic signals carried by the Kuroshio.
According to eddy advection dynamics, both the large-scale circulation and mesoscale eddies are in quasi-geostrophic equilibrium and do not have their own channels for energy dissipation, while one of the direct results of the eddy-mean current interaction is to provide an energy cascade that results in dissipation on non-geostrophic equilibrium submesoscale structures. In the cascade process, ocean energy is not simply transferred between large and small scales, but from the region where it is forced (i.e., the “source”, mainly at the sea surface) to the region where it is most strongly dissipated (i.e., the “sink”, including the surface, seafloor and coastal (i.e., surface, seafloor and coastal areas). Based on this, the energy spectrum and Lorentzian energy cycle are used to analyze and explain the source and sink distribution of oceanic energy and energy cycle in the Kuroshio of Taiwan Island and the East China Sea. Specifically, the Mann-Kendall trend test is firstly used to screen out the typical eddies interacting with the Kuroshio. The kinetic energy conversion and the reasons of eddy deformation during the eddy-Kuroshio interaction are further analyzed. The detailed findings of the study are as follows.
There are multi-spatial-scale ocean dynamic processes in the Kuroshio Current region, so the budget of energy source and sink in this area can describe the oceanic energy cycle and transformation more accurately. The slope of the one-dimensional spectral energy density varies between -5/3 and -3 in the wavenumber range of 0.02-0.1 cpkm, indicating an inverse energy cascade in the Kuroshio of Taiwan Island and the East China Sea. According to the steady-state energy evolution, an energy source must be present. The locations of energy sources were identified using the spectral energy transfer calculated by 24 years of Ocean General Circulation Model for the Earth Simulator (OFES) data. At the sea surface, the kinetic energy (KE) sources are mainly within 23.2°-25.6°N and 28°-29°N at less than 0.02 cpkm and within 23.2°-25°N and 26°-30°N at 0.02-0.1 cpkm. The available potential energy (APE) sources are mainly within 22°-28°N and 28.6°-30°N at less than 0.02 cpkm and within 22.6°-24.6°N, 25.4°-28°N and 29.2°-30°N at 0.02-0.1 cpkm. Beneath the sea surface, the energy sources are mainly above 400 m depth. Wind stressand density differences are primarily responsible for the KE and APE sources, respectively. Once an energy source is formed, to maintain a steady state, energy cascades (mainly inverse cascades by calculating spectral energy flux) will be engendered. By calculating the energy flux at 600 m depth, KE changes from inflow (sink) to outflow (source), and the conversion depth of source and sink is 380 m. However, outflow of the APE behaves as the source.
Eddy-mean flow interactions have always been of interest to researchers because they are among the causes of energy cascades. Different from most previous studies, this research concentrates on the Kuroshio’s effect on the eddy during multiple independent elliptical eddy-Kuroshio interactions. Eddy deformation during the eddy-Kuroshio interaction is applied as the statistical criteria to select the typical eddies interacting with the Kuroshio east of Taiwan. There are 9 anticyclonic eddies (AEs) and 15 cyclonic eddies (CEs) that satisfy the criteria from the 1993 to 2018 satellite altimeter data. The blocking effect caused by the anti-phase velocity at the contact interface of the CE and Kuroshio results in the eddy kinetic energy (EKE) at the CE edge being obviously inhomogeneous, while the AE does not result in the effect. Moreover, the temporal variation in EKE during eddy-Kuroshio interactions precedes the AE/CE deformation by approximately 0.55/0.27 interaction cycles, respectively. The Kuroshio has different modulation mechanisms for different eddy polarities. By calculating the energy budget, the AE EKE is mainly generated by barotropic instability, while the CE EKE is generated by both barotropic and baroclinic instability. The advection effect of the AE on the Kuroshio is in anti-phase with that of the Kuroshio on the AE, which eventually makes the AE shrink. They are in phase for the CE and lead the CE to eventually become meandering.
|王茹. 东海黑潮流域内涡-流相互作用的能量转换特征研究[D]. 中国科学院海洋研究所. 中国科学院大学,2022.|
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