菲律宾以东海域次表层涡的基本特征与输运效应研究

IOCAS-IR

	菲律宾以东海域次表层涡的基本特征与输运效应研究
	宋玮琦
学位类型	博士
导师	张林林
	2024-05-20
学位授予单位	中国科学院大学
学位授予地点	中国科学院海洋研究所
关键词	次表层中尺度涡，垂直结构，涡致水文异常，地理分布，涡致输送，菲律宾以东
摘要	中尺度涡表现为海洋中密集分布的封闭旋转流体，它们对海洋中的能量平衡、物质输送乃至气候变异都具有重要影响。热带西太平洋三维环流结构错综复杂，为中尺度涡的产生提供了有利条件，其中，表层中尺度涡因其在海面有显著信号而易于被卫星高度计探测，丰富的观测资料使得表层中尺度涡的相关研究已经较为广泛；而次表层中尺度涡因其核心通常位于温跃层之下而难以被高时空覆盖率的遥感观测捕捉，其观测研究主要依靠有限的水文断面或潜标阵列调查。此前研究显示菲律宾以东海域是热带西太平洋次表层中尺度涡的高发海区,这些涡旋在调节西边界流季节内变异以及南北半球水团热盐交换过程中扮演重要角色。然而，由于针对性的目标观测较少，对这些次表层涡的空间结构、温盐特性、可能的来源以及涡致输运效应等问题的认识仍不清晰。因此，本文综合观测和模式资料，对上述问题做了系统的探究，主要研究成果如下：（1）基于菲律宾以东 8°N 断面 CTD 观测和棉兰老岛附近水下滑翔机观测，本文首次揭示了该海域次表层中尺度涡大水深透镜状的垂向密度结构本文着重分析了水文观测在菲律宾以东海域捕捉到的三个次表层反气旋涡的个例。它们的水平尺度相近，约 200 公里；垂向密度结构都呈凸透镜状，涡旋核心之上的密度面向上抬升，核心之下的密度面向下压缩。其中，位于 8°N 断面上的两个次表层涡的核心位于 800-1000 米，垂向范围超过 1500 米；而另一个位于棉兰老岛东南侧的次表层涡的核心较浅，位于~300 米。三个次表层涡的温盐性质呈现明显差异：其中两个涡旋具有“高盐核心”，在密度面坐标系上的盐度异常可达 0.1-0.2 psu；而另一个则未携带明显的温盐信号。综合潜标观测和气候态盐度分布的分析推断了这三个次表层涡的可能来源：携带高盐信号的两个次表层涡分别来自 8°N 断面的东侧以及棉兰老岛东南侧（~130°E, ~2°N）附近；另一个不携带温盐信号的次表层涡则来自 8°N 断面的南侧/东南侧。次表层涡的西向移动速度（~5.2 cm/s）和垂直模态投影表明其与第二斜压罗斯贝波相似。（2）基于涡分辨率的模式资料，本文系统地探究了菲律宾以东海域次表层中尺度涡在平均态上的地理分布、垂直结构、温盐特性等基本特征，进而揭示了其涡致输运效应考虑到个例分析难以揭示该海域次表层涡的普遍特征，本研究进一步利用高分辨率数值模式资料（OFES），探究了该海域次表层涡旋的统计特征和涡致输送效应。本文提出了一套次表层涡的判别方法，能有效地分离表层涡和次表层涡；2009-2019 年期间，该方法在菲律宾以东海域共筛选出 3103 个次表层涡，其中反气旋涡的数量远大于气旋涡（反气旋涡 1927 个，气旋涡 1176 个）。合成的次表层涡的垂直结构呈现与观测特征相似的透镜状结构，核心位于 400-500 米，反气旋涡的核心更深，且具有更显著的次表层强化特点。本文还定义了“等效半径”参数用于评估次表层涡捕获水体的能力，结果显示气旋涡和反气旋涡捕获水体的垂向结构存在明显差异。在 400 米以浅，反气旋涡捕获水体的“等效半径”小于气旋涡，即反气旋涡捕获水体的能力弱于气旋涡；而在 400-1300 米之间，情况正好相反。在以上基础上，本文估算了次表层涡引起的体积及热盐输送的空间分布。次表层涡可引起显著的纬向体积输送，主要集中在北赤道流区域，约 1-2 Sv，沿132°E 断面从 8°N 积分至 18°N 的西向体积输送约 12 Sv，约为北赤道流西向输运的 30-40 %；经向体积输送相对较弱，且具有明显的空间分布特点。涡致热盐输送主要集中在棉兰老岛沿岸，涡旋搅拌效应引起的热盐输运比捕获效应大 1-2个数量级。次表层涡搅拌水体向赤道输送的热量约 2.7×10⁷ W/m，沿 9°N 断面作经向积分（125°E-130°E）可达 1.04×10¹³ W。在中层（200-2000 米）次表层涡向北的盐输送达 100kg∙m^-1 ∙s ^-1 ,沿 8°N 断面作经向积分（125°E-130°E）可达 4.03×10⁷kg∙s ^-1，该盐输送量约为棉兰老潜流平均盐输送量的 24%，体现了次表层涡在南北半球水团交换中的重要作用。本研究综合观测数据与模式资料，系统探究了菲律宾以东海域次表层涡的基本特征及涡致输运效应，丰富了对该海域次表层涡的认识，有助于进一步理解太平洋与周边海域的物质能量交换。 Mesoscale eddies are characterized by energetic closed rotating fluids, which are ubiquitous in the ocean. They exert significant influences on oceanic energy balance, material transport, climate variability, etc. The complicated three-dimensional circulation in the tropical western pacific provides favorable conditions for the generation of mesoscale eddies. Among them, surface mesoscale eddies are easy to be detected by satellite altimeters because of their evident signals near the sea surface and the relevant studies on them are very extensive. In contrast, due to that dynamical cores of subsurface eddies are usually located beneath the thermocline, it is difficult to observe them through remote sensing with high spatio-temporal coverage. Therefore, studies on subsurface eddies mainly depend on sparse hydrographic measurements or numerical models. Previous studies have shown that the region east of the Philippines is a high occurrence area of subsurface eddies in the tropical western pacific, and these eddies play an important role in regulating the intraseasonal variation of the western boundary currents and interhemispheric intermediate waters exchange. However, due to the few targeted observations, the three-dimensional structure, thermohaline characteristics, possible origins, and eddy-induced transport remain unclear. Therefore, this study systematically explores the above issues based on the observational and numerical data. The primary research results are as follows: (1) Based on the hydrological observations of CTD across the 8N transect and measurements of the spray glider deployed near the Mindanao coast, this study firstly reported the lens-like vertical density structure of subsurface eddies east of the Philippines. This study focused on the hydrographic characteristics of the three subsurface eddies observed by the CTD and spray glider. All of them share the comparable horizontal scale of about 200 km and exhibit a lens-like vertical density structure with isopycnals above the eddy center lifting upward and those below the eddy center depressing downward. The two eddy cases found at the 8°N transect from the CTD observation were located between 800 and 1000 m with vertical extent exceeding 1500 m, whereas the one detected off the Mindanao coast had a shallower core at ~300 m. There are distinct differences among the three eddy cases. Two eddies were both characterized by a “high salinity core” inside, with salinity anomalies of 0.1-0.2 psu at isopycnal surfaces, while the other one tended to contain water masses properties similar with the surrounding water. By analyzing the mooring ADCP measurements and the climatological salinity distribution, the possible origins of the three eddies were investigated. The two eddies containing high salinity cores probably came from the east of the 8°N section and the southeast of Mindanao coast (~130°E, ~2°N), respectively, and the other one which tended to carry no thermohaline signals was speculated to originate from the south/southeast of the 8°N transect The estimated westward velocity of the subsurface eddy was about 5.2cm/s, which was very close to the phase speed of the second baroclinic Rossby wave. Moreover, the result of the vertical modal projection of the dynamic height anomaly associated with the subsurface eddy also indicated its similarity with the second baroclinic Rossby wave. (2) Based on the eddy-resolving model outputs, this study further systematically explored the general characteristics of subsurface eddies east of the Philippines, including their geographic distribution, vertical structure, thermohaline characteristics, and the eddy-induced transport. Considering that it is difficult to reveal the general characteristics of subsurface eddies by the analysis of eddy cases, this study employed a set of numerical model outputs with high-resolution (OFES) to investigate statistical characteristics and eddy-induced transport. A judgement method for subsurface eddies was proposed, which can effectively distinguish subsurface eddies from surface eddies. From 2009 to 2019, this method screened out a total of 3103 subsurface eddies east of the Philippines, among which the number of anticyclonic eddies was much greater than that of cyclonic eddies (1927 anticyclonic eddies and 1176 cyclonic eddies). The composite subsurface eddy showed lens-like structures similar with the observations, and the core was located at 400-500 m. In particular, the core of anticyclonic eddy was deeper, and its subsurface-intensified characteristic was more significant than that of the cyclonic eddy. A parameter of “equivalent radius” was defined to evaluate water trapping ability of subsurface eddies, and it indicated that there existed obvious differences of the water trapping ability between the anticyclonic and cyclonic eddy. Above 400 m, the "equivalent radius" of the anticyclonic eddy is smaller than that of the cyclonic eddy, that is, the ability of the anticyclonic eddy to capture water is weaker than that of the cyclonic eddy, while in the range of 400 to1300 m, the opposite is true. Furthermore, this study investigated the spatial distribution of volume and thermocline transport induced by subsurface eddies. Subsurface eddies can cause significant zonal volume transport of 1-2 Sv, mainly concentrated in the North Equatorial Current region. The westward volume transport integrated from 8°N to 18°N along 132°E section was about 12 Sv, accounting for about 30-40% of westward transport of the North Equatorial Current. The meridional volume transport was relatively weak and has obvious spatial distribution characteristics. The thermohaline transport of subsurface eddies mainly occurred near the Mindanao coast, and the transport induced by the “eddy stirring effect” was 1-2 orders of magnitude larger than that of the “eddy trapping effect”. Eddy stirring heat transport was equatorward with a magnitude of about 2.7×10⁷W/m, and it can reach 1.04×10¹³W integrated from 125°E- 130°E along the 9°N section. In the range of 200-2000 m, the northward salt transport of subsurface eddies can reach 100kg∙m^-1∙s^-1, and it can reach 4.03×10⁷ kg∙s -1 integrated from 125°E-130°E along the 9°N section, which was about 24% of the salt transport of Mindanao Undercurrent. This result indicated that subsurface eddies play an important role in the exchange of water masses in the northern and southern hemispheres. This study enriches the understanding of subsurface eddies east of the Philippines and it promotes to further understand of the mass and energy exchange between the Pacific Ocean and the surrounding seas.
语种	中文
文献类型	学位论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/185227
专题	中国科学院海洋研究所海洋环流与波动重点实验室
推荐引用方式 GB/T 7714	宋玮琦. 菲律宾以东海域次表层涡的基本特征与输运效应研究[D]. 中国科学院海洋研究所. 中国科学院大学,2024.

条目包含的文件
文件名称/大小	文献类型	版本类型	开放类型	使用许可
宋玮琦-博士论文_最终版.pdf（7758KB）	学位论文		限制开放	CC BY-NC-SA	浏览