IOCAS-IR  > 海洋环流与波动重点实验室
四种斜压不稳定的全球分布和季节变化特征
冯岭
学位类型博士
导师刘传玉 王凡
2021-05-24
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
学位名称理学博士
关键词斜压不稳定 垂向结构 涡旋 季节变化 次中尺度不稳定
摘要

斜压不稳定是生成涡旋的重要机制之一,同时,斜压不稳定可根据垂直结构分类分为四类,而不同种类的斜压不稳定可以预测不同种类的涡旋,比如表层振幅最大的Charney surface型可以预测表层涡旋,而次表层振幅最大的Phillips型可以预测次表层涡旋。因此斜压不稳定类型的研究可以为涡旋研究提供一个新思路。本论文主要利用气候态和季节气候态的World Ocean Atlas 2013WOA13)温盐数据和以此计算的地转流数据,研究全球斜压不稳定以及它的季节变化特征。

本文首先基于WOA13气候态数据分析四种全球斜压不稳定的全球分布。研究发现,振幅在表层或底层最大而中间最小的Eady 型不稳定主要分布在南极绕极流(ACC)区域以及北半球高纬的部分区域,振幅在底层最大且向表层衰减的Charney bottom(后文简写为Charney_b)型不稳定基本零星分布在Eady型不稳定周围;振幅在表层最大且向底层衰减的Charney surface(后文简写为Charney_s)型不稳定广泛分布在全球各个区域,但主要集中在南北半球的副热带区域(10–35);振幅在次表层最大的Phillips型不稳定主要分布在低纬区域(5–20)。斜压不稳定的种类可以预测涡旋的种类,Phillips型不稳定的分布区域与观测到的次表层涡旋的空间位置重合度很高,同时Phillips型不稳定振幅最大的位置与次表层涡的核心位置深度相差不大。

斜压不稳定同时具有波动属性,它在ACC区域以及中纬度(25–35)向东传播,而在低纬度和北半球(30S–30N)和北半球高纬度(>50N)向西传播。斜压不稳定波是两个传播速度相反的Rossby波在平均流的Doppler shift作用下耦合形成的。不同种类斜压不稳定波的形成需要的Rossby波和平均流不同。Eady型需要一阶斜压Rossby波和地形Rossby波以及全水深的平均流,Charney_s型需要一阶斜压Rossby波和地形Rossby波以及从表层到临界层深度范围内平均流,Charney_b型需要地形Rossby波和内Rossby波以及从底层到临界层以上0.3(标准化深度)范围内平均流,而Phillips型需要二阶斜压Rossby波和内Rossby波以及临界层上下振幅0.5范围内平均流。(临界层是两个Rossby波相互作用的位置,在该深度不稳定波的相速度与流速相等。)

斜压不稳定有很强的季节变异特征,在除ACC之外的大部分区域,生长率,空间尺度和不稳定类型都具有显著的季节变化特征。本文着重研究三种典型的季节变化现象:黑潮和湾流区域主导不稳定类型的季节转变,热带—副热带流系Charney_sPhillips型不稳定分界线的季节移动,以及副热带区域冬季出现的次中尺度不稳定。

在黑潮和湾流区域,不稳定的变化是由上层海洋的层结变化主导的。冬季的层结弱时, Charney_s型不稳定主导;夏季层结强时 Phillips型不稳定主导,而春季和冬季层结强弱适中时,Charney_sPhillips型不稳定平分秋色。与之相应,冬季表层斜压转化率很强,夏季次表层的斜压转化率很强,而在春秋两季,表层和次表层斜压转化率强度相当。

与黑潮和湾流区域不同,热带-副热带流系不稳定的季节变异主要由地转流的季节变异而非层结决定。在热带—副热带流系,占据热带区域的Phillips型和占据副热带区域的Charney_s型基本以北赤道流(NEC)和副热带逆流(STCC)为界,春夏两季该界线往赤道移动,秋冬季该界线往极地移动。不稳定的季节变异直接影响该该区域的涡旋动能(EKE)的季节变异:热带区域次表层独立的EKE在春夏两季较弱且向赤道收缩,冬春两季较强且向极地扩展。

以上的讨论聚焦的是标准下挑选出的中尺度不稳定,但在该标准下,我们在副热带STCC区域发现了次中尺度Charney_s型不稳定。为了更准确的剔除次中尺度不稳定而仅保留中尺度不稳定,我们制定一个新的更为合理的标准,。进一步地研究发现,中尺度不稳定的生长时间在春季最快,秋季最慢,超前海表面EKE2个月;次中尺度不稳定的生长时间在冬季最快,超前海表面EKE约一个月。

其他摘要

Baroclinic instability (BCI) is one of the most important mechnism to generate eddies, and according to vertical structure, BCIs can be classified into four types, and they can imply the types of mesoscale eddies, for example, Charney_s type BCI with maximum amplitude at surface and Phillips type BCI with maximum amplitude at subsurface, which can predict surface and subsurface eddies, respectively. Therefore, researches about BCI types may bring some new insight into eddies’ researches. In this paper, we use the temperature and salinity data, as well as corresponding geostrophic flow from climatologic and seasonal climatologic World Ocean Atlas 2013 (WOA13) to research global BCIs and their seasonal variations.

We first analyze global distributions of four types of BCIs. We find that Eady type BCIs, with maximum amplitude at surface or bottom and minimum amplitude in the middle depth, generally locate in Antarctic Circumpoler Current (ACC) and high latitudes in north hemisphere; the Charney bottom (short for Charney_b, hereafter) type BCIs, with amplite intensifying at bottom and decaying towards surface, generally scatter around the Eady type BCIs as patches; the surface-intensified Charney surface (short for Charney_s, hereafter) type BCIs, with amplite intensifying at surface and decaying towards bottom, distribute wildly but primarily occur at subtropics (10–35); the Phillips type BCIs, with amplitude intensifying at subsurface and decaying towards surface and bottom, primarily occur in low latitudes ( 5–20). Furthermore, the BCI types can imply types of mesoscale eddies. The locations of the Phillips type BCIs most overlap the locations of obsevred subsurface eddies, and depths of Phillips type BCIs’ maximum amplitude have small difference with core depths of obsevred subsurface eddies.

Baroclinic instabilities can propagate as waves, which propate eastward in ACC and mid-latitude (25–35), and propagate eastward in low latitude (30S–30N) and high latitude in north hemisphere (>50N). The BCI waves are the interaction of two counter-propagating Rossby waves (CRWs) under the Doppler shift of mean flow. The type of CRWs and depth range of mean flow vary with BCI type. The Eady type BCIs demand first baroclinic Rossby waves and topographic Rossby waves, as well as the full-depth mean flow; the Charney_s type BCIs demand first baroclinic Rossby wave and internal Rossby wave, as well as mean flow ranging from surface to critical layer; the Charney_b type BCIs demand topographic Rossby wave and internal Rossby wave, as well as mean flow ranging from bottom to 0.3 (normalized depth) above critical layer; the Phillips type BCIs demand second baroclinic Rossby wave and internal Rossby wave, as well as mean flow ranging from 0.5 above and 0.5 below critical layer. (Critical layer is right the depth where the two CRWs interact, and also the depth where the phase speed of BCI equals to the mean flow.)

The seasonal variations of global BCIs are significant in most regions except ACC, including growth time, wavelenth and types. In this paper, we focus on three typical seasonality of BCIs: transition of dominant BCIs types in the Kuroshio Extension (KE) and Gulf Stream (GS), seasonal migration of border between the Charney_s and Phillips type BCIs in the tropicalsubtropical system, and occurance of submesoscale BCIs in winter in the subtropical.

In KE and GS, the transition of dominant BCI types is due to seasonal variation of upper stratification. The Charney_s type BCIs previal in winter due to weak upper stratification, the Phillips type BCIs prevail in summer due to strong statification, and the Charney_s and Phillips type coexist with similar portion in spring and autumn. Correspondingly, the baroclinic conversion rate (BCR) is strong at surface in winter, and it is strong at subsurface in summer, and the BCR at surface is comparable to that at subsurface in spring and autumn.

Different with KE and GS regions, it’s the seasonal variations of geostrophic flow other than the upper stratification that dominate the seasonal variations in tropicalsubtropical system. In tropical-subtropical system, the boundary of the Phillips type BCIs prevaling in tropical and the Charney_s type BCIs prevailing in subtropical is generally determined by the boundary of North Equatorial Current (NEC) and Subtropical Countercurrent (STCC). The boundary migrates equatorward in spring and summer, and retreats poleward in autumn and winter. The EKE induced by BCIs changes as well: the subsurface EKE independent of surface EKE is weak and shrinks in spring and summer, but it’s strong and extends in autumn and winter.

The mesoscale BCIs discussed above are choosen when , however, under such criterion, there are submesoscale Charney_s type BCIs in STCC. To distinguish submesoscale BCIs from mesoscale BCIs, we define a new criterion, . Furthermore, mesoscale BCIs grow fasters in spring and slowest in autumn, which leads the surface EKE by two months; submesoscale BCIs grow fasters in winter, which leads the surface EKE by a month.

学科门类理学
语种中文
目录

第一章 绪论... 1

第二章 斜压不稳定及分析方法... 10

2.1 线形稳定性分析方法... 10

2.2 数据... 12

2.3 四种不稳定必要生成条件... 12

2.4 多种不稳定共存... 16

2.5 小结与讨论... 18

第三章 斜压不稳定类型的全球分布... 20

3.1 全球斜压不稳定类型分布... 20

3.2 斜压不稳定的海洋状态... 25

3.3 斜压不稳定种类对次表层涡旋及其他种类涡旋种类的预测性... 31

3.4 小结与讨论... 34

第四章 斜压不稳定波的传播特征... 35

4.1 传播方向相反的Rossby 波(CRWs)共振生成斜压不稳定理论... 35

4.2 四种不稳定生成需要的Rossby... 38

4.3 平均流的Doppler效应的量化... 41

4.4 全球不稳定波的传播速度... 46

4.5 小结与讨论... 49

第五章 全球斜压不稳定的季节变化... 51

5.1 全球斜压不稳定类型的季节变化... 51

5.2 黑潮延伸体和湾流区域不稳定类型的季节转变... 52

5.3 热带副热带流系Charney_s型和Phillips型不稳定边界的季节性移动... 58

5.4 中尺度和次中尺度斜压不稳定... 67

5.5 小结与讨论... 73

第六章 总结与展望... 76

6.1 结论... 76

6.2 创新... 79

6.3 展望... 80

参考文献... 82

... 93

附录A 标准模态Rossby波速... 93

附录B 模式中检测到的可能存在的不稳定波... 95

附录C 北赤道流和副热带逆流中心纬度的计算... 96

附录D:论文使用的缩写(按首字母顺序排序)... 97

... 98

作者简历及攻读学位期间发表的学术论文与出海经历... 100

作者简历... 100

在读期间学术论文发表情况... 100

在读期间的出海调查经历... 100

 

文献类型学位论文
条目标识符http://ir.qdio.ac.cn/handle/337002/170644
专题海洋环流与波动重点实验室
推荐引用方式
GB/T 7714
冯岭. 四种斜压不稳定的全球分布和季节变化特征[D]. 中国科学院海洋研究所. 中国科学院大学,2021.
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
博士学位论文—冯岭.pdf(9219KB)学位论文 开放获取CC BY-NC-SA浏览
个性服务
推荐该条目
保存到收藏夹
查看访问统计
导出为Endnote文件
谷歌学术
谷歌学术中相似的文章
[冯岭]的文章
百度学术
百度学术中相似的文章
[冯岭]的文章
必应学术
必应学术中相似的文章
[冯岭]的文章
相关权益政策
暂无数据
收藏/分享
文件名: 博士学位论文—冯岭.pdf
格式: Adobe PDF
所有评论 (0)
暂无评论
 

除非特别说明,本系统中所有内容都受版权保护,并保留所有权利。