海洋环流与波动重点实验室知识库

  印尼海入口处海域靠近赤道，同等强度的海流形成的海平面梯度要比中高纬度地区小一个数量级，增加了在该海域识别海流路径的难度；因此，棉兰老流的路径变化，以前的研究从未揭示。基于卫星高度计的海表地转流数据以及潜标观测结果，本文中首次识别出棉兰老流在印尼海入口处的摆动路径，对棉兰老流摆动路径的时空结构进行了诊断，发现了其强烈的季节至年际摆动现象，并通过水色数据对所识别的棉兰老流的路径进行了辅助验证。这是对棉兰老流路径摆动研究方向的突破。

  本研究将棉兰老流路径以北、6.5°N以南、129°E以西的海域面积定义为回转指数，来代表棉兰老流在印尼海入口处的摆动。研究结果表明，棉兰老流在印尼海入口处的摆动表现出明显的季节周期：冬季时期，棉兰老流深度入侵北马鲁古海，此时棉兰老流的回转路径处于“入侵态”；春季棉兰老流开始向北移动；夏季棉兰老流到达塔劳岛以北，基本退出北马鲁古海，此时棉兰老流的路径处于“阻塞态”；秋季则再度入侵北马鲁古海，形成一个完整的循环周期。

  棉兰老流的摆动会在印尼海入口处产生一个低浓度叶绿素锋面，该锋面的季节变化与棉兰老流的季节摆动同步。冬春季节时，叶绿素锋面位于塔劳-哈马黑拉岛海峡中；夏季时期锋面向北移动与塔劳岛相接。这是因为棉兰老流来自于开阔大洋，携带着低浓度叶绿素的水团向南流动；而印尼海入口海域通过径流以及水平混合获得了大量营养物质，水体中具有高浓度的叶绿素；当棉兰老流流经印尼海入口时，两种不同浓度的水团发生交汇便会在印尼海入口处形成叶绿素锋面。

  棉兰老流与北赤道逆流的超前滞后相关性分析表明，棉兰老流在印尼海入口处的摆动与北赤道逆流的季节变化存在显著的滞后相关性，这说明棉兰老流在印尼海入口处的摆动受到北赤道逆流变化的影响，而非棉兰老流的摆动诱发北赤道逆流的变化。北赤道逆流的体积输运量变化以及流轴纬度的西向传播速度与第一斜压模的罗斯贝波波速一致；季节性罗斯贝波产生于赤道中-东太平洋海域大约150°W附近，经过大约3个月的时间会到达140°E-150°E附近海域；之后罗斯贝波继续西传进入印尼海入口处，从而诱发了棉兰老流在印尼海入口的季节摆动。

  年际时间尺度上，棉兰老流的摆动与印尼海入口的叶绿素锋面变化同步，超前Niño3.4指数两个月。厄尔尼诺爆发前，回转指数为正的年际异常，表明棉兰老流深度入侵北马鲁古海；拉尼娜期间为负异常，表明棉兰老流向北退回至塔劳岛以北。ENSO期间的合成分析结果表明，相比于厄尔尼诺事件，棉兰老流的年际变化对拉尼娜事件更加敏感；这是因为在拉尼娜事件的冬季，棉兰老流的平衡态发生了改变，棉兰老流的平衡态由入侵态转变为阻塞态，而厄尔尼诺冬季期间则维持在入侵态；平衡态的改变使得棉兰老流在拉尼娜事件期间发生的变化比厄尔尼诺事件期间更强且更持久。在连续拉尼娜事件期间，棉兰老流的路径有维持在阻塞态的趋势，特别是第一年夏季的回退程度比气候态季节性回退更显著。研究发现，棉兰老流的摆动超前于ENSO事件2-3个月，这表明棉兰老流的摆动有可能对赤道热输送和动力平衡起到非常重要的作用，对厄尔尼诺事件的发展产生影响。2-3个月的时间与开尔文波从西边界传入东太平洋冷舌区的时间尺度相吻合，认为可以诱发Bjerknes正反馈，该影响通过开尔文波的解析解得到证明。具体的动力机制在未来工作中会进一步揭示。

  本文的最后一部分，比较了2014和2015/2016年厄尔尼诺事件的发展过程中棉兰老流的路径变化，研究发现在2014年厄尔尼诺事件的启动过程中，棉兰老流主流在夏季（7-8月）突然退出北马鲁古海，可能是导致这一年厄尔尼诺事件突然结束的主要原因。这一变异的具体动力机制，将在未来研究中，通过数值实验深入探讨。

The sea level gradient formed by currents at the gateway of the Indonesian seas is an order magnitude smaller than in mid to high latitude due to the proximity to the equator, which increases the difficulty of identifying the path of current; therefore, the movement of the MC retroflection has never been revealed by previous studies. Based on surface geostrophic currents of satellite altimeter and mooring observations，the movement of the MC retroflection at the gateway of the Indonesian Sea is identified for the first time in this paper, and the spatial-temporal structure of the MC retroflection is diagnosed with the strong seasonal and interannual movement are found, the identified path of the MC is also auxiliary verified by the water color data. These are breakthroughs in the study of the Mindanao Current.

In this study, the retroflection index is calculated as the area of the MC retroflection to represent the variations of the MC path in this study, which is the area surrounded by the MC axis, south of 6.5°N, and west of 129°E.The results show that the MC retroflection has a clear seasonal cycle: The MC intrudes into the Northern Maluku Sea deeply in winter, stays in the equilibrium state of penetration; moves gradually northward in boreal spring; essentially retroflects eastward north of the Talaud Island in boreal summer without intruding into the Maluku Sea, stays in the equilibrium state of choke. The MC then intrudes into the Maluku Sea again in fall to repeat the annual cycle.

The study shows that the MC retroflection produces a Sea Surface Chlorophyll (SSC) front at the gateway of the Indonesian seas, move synchronously with the MC retroflection. The SSC front lies in the Talaud-Halmahera Channel (TH Channel) in boreal winter and spring, while moves northward and touches the Talaud Island in summer. The Mindanao Current, which comes from the open ocean, carries low chlorophyll concentration waters. In contrast, the Indonesian seas, which receive large amounts of nutrients from runoffs and horizontal mixing, contain high chlorophyll concentration waters. The meeting of the two water masses generates a chlorophyll front at the gateway of the Indonesian seas.

The lead-lag correlation between the Mindanao Current and the North Equatorial Countercurrent indicates that there is a high lagged correlation between the MC retroflection and the NECC seasonal variations, which suggests that the movement of the MC retroflection is affected by the NECC seasonal variations, rather than that the movement of the MC retroflection inducing the NECC seasonal variations. The study shows that the westward propagation speed of the NECC transport changes and its axis latitudes are in agreement with the first baroclinic mode of the Rossby waves. The seasonal Rossby waves are generated in the central-eastern equatorial Pacific at around 150°W, which take around three months to arrive at the area of 140°E-150°E; after reaching the area of 140°E-150°E, the Rossby waves continues to propagate westwards into the gateway of the Indonesian seas and induce the variations of MC retroflection.

On interannual time scales, the MC retroflection and SSC front are found to move synchronously. The interannual anomalies of the retroflection index tend to be positive and the MC retroflection intrudes into the northern Maluku Sea deep during the El Niño year, while tend to be negative and the MC retroflects eastward north of the Talaud Island in the La Niña year. The composite ENSO events show that the interannual variations of the retroflection index are more sensitive to La Niña events than to El Niño events. During La Niña winters, the equilibrium states of the MC retroflection change from the penetration to choke states, whereas stay in an anomalously deep penetrating path during El Niño winters. The changes of the equilibrium state causing stronger and longer La Niña-induced variations than those induced by the El Niño. During consecutive La Niña events, there was a tendency for the MC to stay in the leaping path, and the strength of retreat is stronger in the summer of first year than the climatological seasonal retreat. It is found that the movement of the MC retroflection lads the ENSO event by 2-3 months, which suggests that the movement of the MC has the potential to play a very important role in the equatorial heat transport and dynamical balance, and have an impact on the development of the El Niño event. 2-3 months coincides with the timescale for the propagation of the Kelvin wave from the western boundary to the cold tongue region of the eastern Pacific Ocean, which is thought to induce the Bjerknes feedback. The effect of the MC is proved by the analytical solution of the Kelvin wave. The specific dynamical mechanisms will be further revealed in future studies.

At the end of this paper, the movements of the MC retroflection during the development of the 2014 and 2015/2016 El Niño events is compared. During the initiation of the 2014 El Niño event, the Mindanao Current shifted out of the Maluku Sea abruptly in the summer (July-August) of 2014, may have been the main reason for the abrupt end of the El Niño event in that year. The exact dynamics of this variation will be further explored through numerical experiments in future studies.

第1章 绪论... 1

1.1 研究意义和背景... 1

1.2 研究现状... 2

1.2.1 热带西太平洋环流结构... 2

1.2.2 印尼海入口处的历史观测... 3

1.2.3 印尼海入口处表层环流研究... 9

1.2.4 西边界流非线性碰撞理论... 17

1.2.5 厄尔尼诺现象发展机制的研究... 18

1.3 主要内容与章节安排... 20

第2章 数据和方法... 23

2.1 潜标数据... 23

2.2 卫星遥感数据... 25

2.2.1 卫星叶绿素数据... 25

2.2.2 卫星高度计数据... 25

2.2.3 AVHRR海表面温度数据... 26

2.3 其他数据... 26

2.3.1 绝对地转流数据... 26

2.3.2 TAO/TRITON浮标阵列数据... 27

2.3.3 NECP风场数据... 28

2.3.4 Niño3.4指数... 28

2.4 主要研究方法... 29

2.4.1 印尼海入口处棉兰老流路径的识别方法... 29

2.4.2 巴特沃斯（Butter-worth）低通滤波... 29

2.4.3 潜标ADCP数据质量控制与预处理... 29

2.4.4 罗斯贝波波速计算... 30

2.4.5 一元线性回归... 32

2.4.6 体积输送量计算... 32

2.4.7 相关系数及显著性检验... 33

第3章 棉兰老流在印尼海入口处的季节变化特征... 35

3.1 引言... 35

3.2 潜标数据与海表地转流数据的对比分析... 35

3.2.1 TH海峡潜标数据... 35

3.2.2 海表地转流数据与潜标数据的对比结果... 37

3.3 棉兰老流的季节摆动规律及其影响... 40

3.4 棉兰老流与北赤道逆流的联系... 44

3.5 本章小结... 48

第4章 棉兰老流在印尼海入口处的年际变化特征及其影响... 51

4.1 引言... 51

4.2 棉兰老流的年际变化特征... 51

4.2.1 棉兰老流在印尼海入口处的年际摆动... 51

4.2.2 不同ENSO事件的合成分析结果... 54

4.2.3 棉兰老流的摆动对厄尔尼诺事件的影响... 57

4.2.4 连续拉尼娜事件中的棉兰老流路径... 59

4.3 2014年和2015/2016年厄尔尼诺事件发展阶段的对比讨论... 63

4.3.1 2014和2015年棉兰老流路径的差异... 63

4.3.2 2014和2015年厄尔尼诺发展阶段的对比分析... 70

4.3.3 2023/2024年和1997/1998年的厄尔尼诺事件... 74

4.4 本章小结... 77

第5章 总结与展望... 81

5.1 主要结论... 81

5.2 本文创新点... 83

5.3 未来工作展望... 83

参考文献... 85

附录 常用简称索引表... 95

致 谢... 97

作者简历及攻读学位期间发表的学术论文与其他相关学术成果... 99