IOCAS-IR  > 海洋环流与波动重点实验室
菲律宾以东海域次表层涡动能的季节与年际变异规律
惠玉超
Subtype博士
Thesis Advisor张林林
2022-05-19
Degree Grantor中国科学院大学
Place of Conferral中国科学院海洋研究所
Degree Name理学博士
Keyword热带西太平洋 次表层涡动能 季节、年际变化 正压、斜压转换率 Rossby波 ENSO
Abstract

热带西太平洋拥有全球最大的暖水体—暖池和复杂的环流系统,在全球气候系统中扮演重要角色,对我国的气候环境也具有重要影响。该海域复杂的流系结构为中尺度涡旋尤其是次表层中尺度涡旋的产生提供了有利条件,特别是菲律宾以东海域,是热带西太平洋次表层涡旋活动最为活跃的海区。中尺度涡可以将风场输入到大尺度环流中的能量传递到更小的尺度中去,在海洋能量循环过程中起着承上启下的作用。同时,中尺度涡有很强的非线性,可以携带水体进行长距离位移,对西太平洋次表层水团输运有重要影响。因此,开展菲律宾以东海域次表层中尺度涡旋研究对认识西边界流系多尺度变异规律、理解海洋能量循环过程及水团输运过程具有重要意义。
本文基于潜标ADCP观测和高分辨率模式等数据,从能量学角度出发研究了菲律宾以东涡动能(EKE)的空间分布特征,探究了该海域次表层EKE的季节和年际变异规律及其机制,还利用时空分辨率更完善的Argo数据,刻画了太平洋次表层海水温度的季节变化特征。研究结果揭示了背景流场的正压不稳定在菲律宾以东海域次表层EKE生成和变异中的重要作用,修正了传统观念中认为的斜压不稳定过程是该海域次表层涡旋主要能量来源的观点。
基于局地多尺度能量学分析方法(MS-EVA),本文首先利用OFES模式数据探究了热带西太平洋EKE的空间分布特征。在上层(0-200m),EKE高值区主要分布在北赤道逆流(NECC)源区以及苏拉威西海。在次表层(300-700m),EKE的高值区则主要集中在130ºE以西的菲律宾沿岸。EKE收支结果表明,背景流场的局地不稳定过程是这些涡旋能量来源的主要途径,非局地过程对EKE的空间再分配仅限于EKE高值区域内部。在上层,背景流场的正压不稳定过程是EKE能量的主要来源,在次表层,正压和斜压不稳定都起着重要贡献,并且正压不稳定的贡献集中在菲律宾东岸的南部,斜压不稳定的贡献则主要集中在北部。
基于传统能量分析方法,本文进一步利用潜标ADCP数据和2000-2017年OFES模式数据,揭示了菲律宾以东海域次表层EKE的季节变化特征及其控制机制。在菲律宾沿岸以东至130ºE以西,5º-14ºN之间存在显著的次表层EKE信号(300-700m),该EKE信号通过200m深度上的EKE极小值明显地与表层EKE分开。以10ºN为分界线,次表层EKE在南部和北部区域呈现出几乎相反的季节变化。在北部区域,EKE在早春达到最大值,夏季达最小值。而在南部区域,EKE在夏季达最大值,冬季达最小值。进一步的研究表明,虽然背景流场的正压和斜压不稳定在次表层EKE生成过程中都有贡献,但是EKE的季节变化主要受正压不稳定的调控,并且该区域北部和南部正压不稳定的季节演变分别与北赤道潜流(NEUC)和哈马黑拉涡(HE)的季节变化有关。
在理清了菲律宾以东次表层EKE季节变化的基础上,本文基于更长时间序列的OFES模式数据(1995-2017)和潜标观测数据,进一步研究了其年际变化规律,并分析了与ENSO的关系。结果显示,菲律宾以东次表层EKE具有显著的年际变化信号,并且年际信号的强度大于季节信号。EKE的年际变化与ENSO有关,其年际变化滞后于Nino 3.4指数约14个月。能量诊断结果表明,次表层EKE年际变化主要受背景流的正压和斜压不稳定调控,其中正压不稳定起着主导作用。在菲律宾以东的南部海域,正压不稳定的年际变化受到次表层部分HE变化的控制,在北部主要跟棉兰老潜流(MUC)的年际变化有关。HE和MUC的变化受到ENSO事件的调节,当厄尔尼诺(El Niño)发生时,日界线附近出现海面高度负异常,该异常信号以第一斜压模Rossby波的形式向西传播,对菲律宾以东的西边界流产生迟滞的调节作用,并进一步通过正压不稳定途径影响次表层EKE的年际变化。因此,次表层EKE的年际变化滞后于Nino 3.4指数。由于Rossby波在低纬度海区具有更快的波速,因此在低纬度海域的正压不稳定及其对应的EKE对ENSO事件响应更快。
本文最后还利用2000-2017年的Argo数据,给出了热带太平洋次表层海温的季节变化特征。热带太平洋最强的海温季节信号出现在次表层温跃层深度附近,并且沿着12ºN、5ºN和5ºS三条纬线呈横跨整个热带太平洋的带状分布。进一步的分析表明,温跃层的垂直起伏是次表层海温出现显著季节变化的原因。温度异常信号最先出现在东太平洋,然后逐渐向西传播,最终到达西太平洋附近。风场驱动的第一斜压模Rossby波线性模式很好地模拟出温跃层季节性的抬升和下潜以及对应的次表层温度的季节变化。海盆尺度的风应力旋度的季节变化会导致温跃层起伏,该信号在以Rossby波形式向西传播的过程中导致温跃层深度附近出现显著的温度季节变化。同时温跃层深度的起伏与赤道流系如北赤道流(NEC)、北赤道逆流(NECC)和南赤道流(SEC)流轴的季节性摆动有紧密联系。

 

Other Abstract

The western tropical Pacific has the largest warm water mass—warm pool and complicated circulation system in the world, playing a significant role in the global climate system, having a crucial impact on China's weather and environment. The complex three-dimensional current system in this region provides warm beds for the generation of mesoscale eddies, especially in the region east of the Philippine, which has the most energetic activities of subthermocline eddy in the western tropical Pacific. Mesoscale eddies can transport the energy of the background current field injected by wind to smaller scales, playing a connecting role in the process of ocean energy cycle. Meanwhile, mesoscale eddies with strong nonlinearity can carry water bodies for long-distance transportation, and are essential for the transportation of subsurface water mass in the tropical western Pacific. Therefore, the study of mesoscale eddies in the tropical western Pacific will help us to clarify the multi-scale variations of western boundary currents, deepen our understanding of the process of energy cycle and water mass transportation in the ocean.
Based on subsurface mooring ADCP and high-resolution model outputs, this paper studies the spatially distributed characteristics of eddy kinetic energy (EKE) in the Philippine coast and further investigates its seasonal and interannual modulations. Finally, Argo data with finer spatial-temporal resolution is used to explore the seasonal variation of subsurface temperature in the tropical Pacific. This study emphasizes the importance of barotropic instability of background currents on the generation and modulations of subthermocline mesoscale eddies, and corrects the viewpoint that baroclinic instability progress is the main way that mesoscale eddies get energy from the mean flows in this region. 
The EKE distribution in the western tropical Pacific is firstly studied using the MS-EVA method and OFES outputs. In the upper layer (0-200m), the area with high EKE value is in the NECC source region and Celebes sea, and in the subsurface layer (300-700m), high EKE value mainly concentrates on the east of the Philippine coast. The result of EKE budget indicates that local instability of background flows is the source of EKE, and the contributions of non-local process are limited in the region with high EKE value. In the upper layer, barotropic instability plays a dominant role in the generation of mesoscale eddy, while both barotropic and baroclinic instabilities are essential in the subsurface layer, and, generally, baroclinic instability is dominant in the northern part and barotropic instability is dominant in the southern part.
Based on classical energy analysis method and ADCP measurements and OFES outputs, we then reveal the seasonal variability of subthermocline EKE east of the Philippines and clarify the underlying mechanism. The results indicate that significantly high EKE appears below the thermocline in the latitude band between 5º and 14ºN east of the Philippines. Separated by 10ºN, the EKE in the northern and southern parts of the region shows nearly opposite seasonal cycles, with its magnitude reaching a maximum in early spring and minimum in summer in the northern part and reaching a maximum in summer and minimum in winter in the southern part of the region. Further investigation indicates that although baroclinic and barotropic instabilities are essential in generating the subthermocline eddies, but the seasonal variation of subthermocline EKE is mainly caused by the seasonal modulation of barotropic instability. The seasonal modulation of barotropic instability in the northern and southern part of the region is associated with the seasonal evolution of North Equatorial Undercurrent and Halmahera Eddy, respectively.
On the basis of clarifying the seasonal variability of the subthermocline EKE in the east of the Philippines, we further studied its interannual variation and explored its relationship with ENSO events based on OFES model outputs (1995-2017) and mooring ADCP measurements with longer time periods. The results indicate that the subthermocline EKE shows significant interannual variation that is stronger than seasonal signal, and it’s closely related to the ENSO events, generally behind Nino 3.4 index 14 months. Further energy diagnostic analysis dominates that the interannual variation of subthermocline EKE is controlled by both baroclinic and barotropic instability of the background flows and dominated by the barotropic instability especially. Barotropic instability in the southern part of the Philippine coast is associated with the subsurface component of the quasi-permanent anticyclonic eddy Halmahera Eddy (HE), while that in the northern part is closely related to the Mindanao Undercurrent (MUC). Both HE and MUC are modulated by the ENSO events. When El Niño occurs, negative sea surface height anomalies appear near the dateline and propagate westward in the form of the first mode baroclinic Rossby wave exerting delayed impacts upon the western boundary currents east of the Philippine coast and further modulating the interannual variation of subthermocline EKE. Moreover, the barotropic energy conversion rate and its corresponding subthermocline EKE at lower latitudes responds relatively faster to ENSO due to the higher Rossby wave phase speed there.
Finally, using Argo data from 2000 to 2017, the seasonal variation characteristics of subsurface temperature in the tropical Pacific are completely given. It is found that the strongest seasonal variation is in the subsurface layer corresponding to the thermocline, which is located in three zonal bands centering at 12°N, 5°N and 5°S across the entire tropical Pacific. Further analysis indicates that seasonal variation of subsurface temperature is caused by the vertical movement of the thermocline, and the signal is generated in the eastern Pacific and propagates westward to the western Pacific. A linear wind-driven first-mode baroclinic Rossby wave model is then employed to investigate the seasonal fluctuation of thermocline. The seasonal shoaling and deepening of thermocline and associated temperature variations are well captured by this Rossby wave model. Basin-scale seasonal anomalies of wind stress curl in the tropical Pacific produce significant thermocline fluctuations, which propagate westward in the form of annual Rossby waves, and cause the seasonal variation of subsurface temperature. Thermocline fluctuations are revealed to be tightly associated with the meridional shift of equatorial currents such as North Equatorial Current (NEC), North Equatorial Countercurrent (NECC) and South Equatorial Current (SEC).

 

MOST Discipline Catalogue理学::海洋科学
Language中文
Table of Contents

第1章  绪论 1

1.1  研究意义 1

1.2  研究现状 2

1.2.1  热带西太平洋三维环流结构 2

1.2.2  海洋中尺度涡旋 4

1.2.2.1  表层强化的中尺度涡旋 4

1.2.2.2  次表层强化的中尺度涡旋 5

1.3  本文主要内容及章节安排 7

第2章  数据和方法 11

2.1  研究数据 11

2.1.1  OFES数据 11

2.1.2  潜标ADCP数据 11

2.1.3  Argo数据 12

2.1.4  其他数据 12

2.2  研究方法 12

2.2.1  涡动能和正压\斜压转换率的计算方法 12

2.2.2  局地多尺度能量学分析(MS-EVA) 13

2.2.3  1.5层线性约化重力模式 14

第3章  热带西太平洋涡动能的空间分布及能量收支 17

3.1  热带西太平洋涡动能的空间分布特征 17

3.2  非局地过程对涡动能收支的影响 21

3.3  热带西太平洋涡动能的能量收支 24

3.4 小结 26

第4章  菲律宾以东海域次表层涡动能季节变化及其控制机制 27

4.1  模式数据验证 27

4.2  菲律宾以东海域次表层涡动能的季节变化 28

4.2.1  涡动能的垂直结构 28

4.2.2  涡动能的半年变化 31

4.2.3  涡动能季节变化特征 33

4.3  菲律宾以东海域次表层涡动能季节变异机制 38

4.3.1  次表层涡动能的能量来源 38

4.3.2  与正压\斜压不稳定的关系 39

4.3.3  正压不稳定季节变化的原因 44

4.4  小结 48

第5章  菲律宾以东次表层涡动能年际变化及其与ENSO的关系 51

5.1  模式数据验证 51

5.2  菲律宾以东海域次表层涡动能的年际变化 53

5.2.1  涡动能年际变异特征 53

5.2.2  涡动能的年际变化随纬度的差异 55

5.3  控制菲律宾以东海域次表层涡动能年际变化的机制 57

5.3.1  背景流场不稳定 57

5.3.2  正压不稳定的来源 60

5.4  次表层涡动能的年际变化与ENSO的关系 64

5.5  小结 67

第6章  热带太平洋次表层海温的季节变化 69

6.1  研究背景 69

6.2  热带太平洋次表层海温的季节变化 71

6.2.1  热带太平洋气候态海温分布特征 71

6.2.2  次表层海温的季节变化特征 72

6.3  次表层海温季节变异机制 79

6.4  温跃层的起伏与海流季节变化的联系 81

6.5  小结 83

第7章  总结与展望 85

7.1  本文主要结论与创新点 85

7.2  对未来工作的展望 87

参考文献 89

致  谢 99

作者简历及攻读学位期间发表的学术论文与研究成果 101

Document Type学位论文
Identifierhttp://ir.qdio.ac.cn/handle/337002/178396
Collection海洋环流与波动重点实验室
Recommended Citation
GB/T 7714
惠玉超. 菲律宾以东海域次表层涡动能的季节与年际变异规律[D]. 中国科学院海洋研究所. 中国科学院大学,2022.
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