海洋环流与波动重点实验室知识库

   降水作为最难以准确预测的气象要素之一，对人类社会生产生活和科学防灾减灾具有至关重要的影响。海表温度（sea surface temperature, SST）是降水异常的重要外强迫源，其效应在多个时间尺度上调制着降水的变化。然而，SST对降水的复杂影响导致了多个时间尺度信号混杂在一起，难以有效分离其因果关系。因此，本文利用多窗谱分析—奇异值分解（Multi-Taper Method–Singular Value Decomposition, MTM–SVD）方法对复杂的多尺度信号进行分离和重构，研究中国降水在特定频率上对SST强迫的响应。首先，阐明了中国降水与太平洋和大西洋SST强迫在特定频率分量上的协同演变特征，以及可能涉及到的过程和机制。然后，通过个例分析评估了低频信号不同分量对中国降水变化的相对贡献。最后，通过基于大气环流模式的数值模式试验进一步分析了不同气候模态对中国降水年代际变化的协同影响。本文主要结果如下：

  （1）中国降水和印度—太平洋SST均具有准两年和准五年周期变化信号，这些主导的年际变率分别与中太平洋（central Pacific, CP）型和东太平洋（eastern Pacific, EP）型的厄尔尼诺与南方涛动（El Niño and Southern Oscillation, ENSO）事件相联系。CP型ENSO和南方地区降水之间呈正相关关系，这可能与太平洋-日本（Pacific-Japan, PJ）遥相关型大气响应有关。在EP型El Niño成熟期，中国降水异常南北向呈“+ – +”三极型分布（即华南和华北降水偏多，而长江—黄河流域降水偏少），这可能与西太平洋副热带高压（western Pacific subtropical high, WPSH）的强度偏强和位置偏北有关。进一步发现，两类ENSO信号对1997年冬季和次年夏季的中国降水变化有着不同的影响。在1997年冬季，二者均有利于中国南方降水的增强。在1998年夏季，准两年周期信号可以解释长江中下游（the middle and lower reaches of the Yangtze River, MLYR）以南的降水减少，准五年周期信号在其中起着削弱作用；准两年和准五年周期信号均有利于MLYR以北降水的增多。

  （2）中国东部降水和北太平洋SST均具有11年和23年周期信号。结果显示，通过太平洋年代际振荡（Pacific Decadal Oscillation, PDO）相关的阿留申低压（Aleutian low, AL）异常对WPSH和蒙古高压（Mongolia High, MH）的影响，北太平洋SST强迫可以调节中国降水分布。在11年周期的PDO冷位相（PDO^–）发展期，WPSH和MH的减弱促使长江流域降水增强，而在衰退期偏强的WPSH和MH可以促使雨带北移导致华北降水偏多。在与23年周期相关的PDO^–发展期，WPSH和MH的偏弱会增强华北地区的降水，而衰退期WPSH的偏强而MH的偏弱有利于华南降水的增多。如对1998年夏季强降水个例分析表明，11年和23年变率对中国不同地区降水变化的贡献存在差异。11年周期主要解释MLYR降水的增加，而23年周期可以解释东北降水的增加。

   （3）中国降水和北大西洋SST场均具有13年和23年周期信号。在13年时间尺度上，在北大西洋三极子（North Atlantic Tripole, NAT）正位相时期，中国降水呈东涝西旱型分布。在23年时间尺度上，当北大西洋处于海盆尺度（North Atlantic basin scale, NABS）增暖（NABS⁺）时，中国降水雨带位置偏北，反之亦然。结果显示，北大西洋SST可以通过不同的过程影响MH，进而调制着中国降水的年代际变化。在13年时间尺度上，与NAT位相发展和成熟期相关的北大西洋振荡（North Atlantic Oscillation, NAO）激发出可以传播到东亚的中纬度波列，通过影响MH调制中国的东西反相型降水。在23年时间尺度上，与NABS⁺成熟期相关的SST异常效应通过冰岛低压（Iceland Low, IL）和MH之间的“跷跷板”式变化，有利于NABS⁺发展期华北降水的偏多，促进NABS⁺衰退期华南降水的增强。

（4）进一步使用大气环流模式（ECHAM5）试验验证上述基于资料分析的结果。例如，通过使用MTM–SVD方法构建出与中国降水相关的SST年代际强迫场，来驱动ECHAM5模式可以模拟出对应周期的中国降水响应。在北太平洋SST强迫下，PDO主导着中国降水三极型分布，即PDO暖位相（PDO⁺）增强MLYR的降水而削弱华南—华北的降水；在北大西洋SST强迫下，NABS与华北（西南）降水呈正（负）相关关系。前者与中纬度波列和北太平洋中西部SST共同效应诱发的东亚北部异常高压和偏弱的WPSH有关。后者通过中纬度波列的东亚大气活动中心西移对东亚北部气压异常产生影响，促进（抑制）NABS⁺发展（衰退）期华北降水的增强。在北太平洋和北大西洋SST的共同作用下，中国降水异常呈经向偶极型分布。降水雨带在PDO⁺时位于华南，在NABS⁺时位于MLYR以北。PDO⁺和NABS⁺的依次出现可以造成降水雨带具有与观测较为一致的年代际北移特征。

   本论文通过对复杂的多时间尺度信号进行分离和重构，建立了中国降水和SST在给定时间尺度上的关系，阐明了中国降水与ENSO、PDO、NAT和NABS等模态在不同频率分量上的协同演变特征，完善了气候模态影响中国降水多时间尺度变率的过程和机制，并进一步揭示出不同信号分量对于中国降水变化的相对贡献差异以及北太平洋和北大西洋SST组合对中国降水年代际变化的协同影响。这些结果有助于增强我们对中国降水多时间尺度变率形成机理的理解和认识，对提高降水预测的准确性和可靠性具有十分重要的科学和现实意义。

Precipitation, which is one of the most challenging meteorological elements to forecast accurately, has vital impacts on social production and life, as well as scientific disaster prevention and mitigation. Sea surface temperature (SST) is a critical external forcing of precipitation, with its anomaly playing a significant role in the precipitation variations over China on multi-time scales. However, the complex effects of climate modes on precipitation result in signals from various time scales being intertwined, making it difficult to effectively isolate their causative relationships. Therefore, this study investigates the response of precipitation to SST forcing at different frequencies by using the Multi-Taper Method–Singular Value Decomposition (MTM–SVD), which can separate and reconstruct complex signals. This study discusses the co-evolution characteristics of precipitation over China and North Pacific / North Atlantic SST at a specific frequency component, along with possible processes and mechanisms involved. Moreover, the relative contributions of different signal components in the low-frequency bands to the precipitation variations over China are evaluated by precipitation case analysis. Finally, the synergistic interdecadal effects of various climate modes on precipitation over China are quantified by numerical model experiments based on the atmospheric circulation model. These results will deepen our knowledge of the mechanisms behind the interannual to interdecadal variabilities of precipitation over China and have important implications for improving precipitation forecast accuracy. The main results of this study are as follows:

(1) Precipitation over eastern China and SST in the Indo-Pacific exhibit quasi-biennial and quasi-five-year cycle signals, which are associated with El Niño and Southern Oscillation (ENSO) events of the central Pacific (CP)-type and the eastern Pacific (EP)-type, respectively. The CP-type ENSO is positively correlated with precipitation anomalies south of the middle and lower reaches of the Yangtze River (MLYR), which may be related to the Pacific-Japan (PJ) type atmospheric response. During the mature stage of the EP-type El Niño, precipitation distribution over China showed a “+ – +” tripolar pattern (that is, precipitation increases over South China and North China, and decreases over the Yangtze River-Yellow River Basin), which may be resulted from the western Pacific subtropical high (WPSH) enhanced and moved northward. As shown by the precipitation case of 1997/1998, the two types of ENSO have different effects on the interannual variations of precipitation over China. Their effects both contributed to precipitation increase over the south of MLYR in the winter of 1997. In the summer of 1998, the quasi-biennial cycle signal mainly accounts for the precipitation decrease south of the middle and lower reaches of the Yangtze River (MLYR), and quasi-five-year cycle signal plays a weakening effect in it; the quasi-biennial and quasi-five-year cycle signals both contributed to precipitation increase north of the MLYR.

(2) Two significant signals, one with 11-year cycle and the other with 23-year cycle, are identified both in the precipitation and North Pacific SST fields. Results show that the North Pacific SST forcing modulates the precipitation distribution over China through the effects of the Pacific Decadal Oscillation (PDO)-related anomalous Aleutian low on the WPSH and Mongolia High (MH). During the development stage of the PDO cold phase (PDO^–) associated with the 11-year cycle, the weakened WPSH and MH increase the precipitation over the Yangtze River Basin, whereas the intensified WPSH and MH cause the enhanced rain band to move northward to North China during the decay stage. During the development stage of the PDO^– associated with the 23-year cycle, the weakened WPSH and MH increase the precipitation over North China, whereas the intensified WPSH and the weakened MH increase the precipitation over South China during the decay stage. The 11-year and 23-year variabilities make different contributions to the precipitation variations in the different regions of China, as seen in the 1998 flooding case. The 11-year cycle mainly accounts for the precipitation increase over the MLYR, while the 23-year cycle is responsible for the precipitation increase over Northeast China.

(3) Precipitation over China and the North Atlantic SST fields both exhibit 13-year and 23-year cycle signals. For the 13-year cycle, the North Atlantic Tripole (NAT) positive phase dominates the precipitation distribution with an east flooding and west drought pattern. For the 23-year cycle, North Atlantic basin scale warming (NABS⁺) can promote the position of precipitation rain belt to move northward, and vice versa. The effects of the North Atlantic SST by which affect the MH through different processes modulating the precipitation variation over China. For the 13-year cycle, the North Atlantic Oscillation (NAO) associated with the development-maturation of the NAT phase can excite mid-latitude wave trains propagating to East Asia and modulate the east-west anti-phase type precipitation over China by affecting the MH. For the 23-year cycle, accompanied by an out-phase variation between Iceland Low (IL) and MH during the mature stages of the NABS⁺, the effects of SST are conducive to precipitation increase over North China (South China) during the development (decay) stages of the NABS⁺.

(4) Furthermore, the atmospheric circulation model (ECHAM5) was used to verify the data analysis results. For example, the ECHAM5 model can simulate the corresponding cycle responses of precipitation over China by using the MTM-SVD method to construct the interdecadal SST forcing field related to precipitation. Under the North Pacific SST forcing, The PDO is closely related to the tripolar-type precipitation distribution over China. Under the North Atlantic SST forcing, the NABS has a positive (negative) correlation with the precipitation over North China (Southwest). The former is related to the SLP over northern East Asia and WPSH changes induced by the combined effects of mid-latitude wave trains and SST in the central and western North Pacific. The latter is affected by the westward shift of the East Asia atmospheric activity center associated with mid-latitude wave trains, which promotes (inhibits) the occurrence of precipitation over North China during the development (decay) stages of the NABS⁺. Under the combined effects of SST in the North Pacific and North Atlantic, precipitation anomalies distributed over China exhibit a meridional dipole pattern. The precipitation rain belt is located in the south of China during the PDO warm phase (PDO⁺) and in the north of MLYR during the NABS⁺. When the PDO⁺ and the NABS⁺ appear sequentially, the precipitation rain belt has an interdecadal northward shift, which is consistent with observations.

In this study, by isolating and reconstructing the complex multi-scale signals, the relationships between precipitation over China and SST on a given time scale are established. The characteristics of the precipitation covarying with the ENSO, PDO, NAT, and NABS modes on different frequency components are clarified. The process and mechanism of the climate modes affecting the multi-time scale variability of precipitation are improved. Furthermore, the relative contribution differences of distinct signal components in precipitation changes over China are shown, as are the synergistic interdecadal effects of the SST in the North Pacific and North Atlantic on precipitation variations. These findings contribute to a better understanding of the mechanisms underlying China's precipitation multi-time scale variability and have significant scientific and practical implications for enhancing the accuracy and reliability of precipitation prediction.

目  录

第1章 绪论... 1

1.1 研究背景和意义... 1

1.2 国内外研究进展... 2

1.2.1 中国降水的时空分布特征... 2

1.2.2 东亚大气环流对中国降水的影响... 3

1.2.3 印度—太平洋海温对中国降水的影响及机制... 4

1.2.4 大西洋海温对中国降水的影响及机制... 8

1.2.5 气候模态的组合效应对中国降水的影响... 8

1.3 关键科学问题以及本文的主要研究内容... 9

第2章 数据和方法... 11

2.1 数据来源... 11

2.2 研究方法... 11

2.2.1 多窗谱分析—奇异值分解（MTM–SVD）... 11

2.2.2 ECHAM5大气环流模式介绍... 13

2.2.3 水汽通量及其散度... 14

第3章 中国降水与ENSO年际协同演变... 17

3.1 引言... 17

3.2 数据和方法... 17

3.3 中国降水和印度—太平洋海温的周期分析... 18

3.4 准两年周期重构的时空演变特征... 20

3.4.1 降水和海温的主导模态... 20

3.4.2 降水和海温的协同演变特征... 21

3.4.3 影响机制... 23

3.5 准五年周期重构的时空演变特征... 27

3.5.1 降水和海温的主导模态... 27

3.5.2 降水和海温的协同演变特征... 27

3.5.3 影响机制... 29

3.6 1997冬季和1998年夏季降水的个例分析：组合效应... 31

3.7 本章小结... 35

第4章 中国降水与PDO的年代际协同演变... 37

4.1 引言... 37

4.2 数据和方法... 37

4.3 降水与海温的主导周期特征... 38

4.4 11年周期重构的时空演变特征... 40

4.4.1 降水和海温的主导模态... 40

4.4.2 降水与海温的协同演变特征... 41

4.4.3 影响机制... 42

4.5 23年周期重构的时空演变特征... 46

4.5.1 降水与海温的主导模态... 46

4.5.2 降水与海温的协同演变特征... 47

4.5.3 影响机制... 49

4.6 1998年夏季强降水事件的个例分析：组合效应... 52

4.7 本章小结... 54

第5章 中国降水和北大西洋SST的年代际协同演变... 57

5.1 引言... 57

5.2 数据和方法... 57

5.3 中国降水和北太平洋海温的周期分析... 58

5.4 13年周期重构的时空演变特征... 59

5.4.1 降水和海温的主导模态... 59

5.4.2 降水和海温的协同演变特征... 61

5.4.3 影响机制... 63

5.5 23年周期重构的时空演变特征... 67

5.5.1 降水和海温的主导模态... 67

5.5.2 降水和海温的协同演变特征... 68

5.5.3 影响机制... 70

5.6 本章小结... 72

第6章 ECHAM5模式对中国降水年代际变化的模拟... 73

6.1 引言... 73

6.2 数据和方法... 74

6.2.1 构建模式强迫场... 74

6.2.2 模式性能评估... 78

6.3 模拟的降水主导周期... 79

6.4 北太平洋SST年代际试验（PAC试验）... 82

6.4.1 中国降水的年代际模态... 82

6.4.2 降水和SST的协同演变特征... 84

6.4.3 影响机制... 85

6.5 北大西洋SST年代际试验（ATL试验）... 90

6.5.1 中国降水的年代际模态... 90

6.5.2 降水和SST的协同演变特征... 91

6.5.3 影响机制... 92

6.6 北太平洋和北大西洋SST对降水的年代际协同作用... 95

6.6.1 中国降水对海温协同效应的响应特征... 95

6.6.2 影响机制... 99

6.7 本章小结... 102

第7章 总结和展望... 105

7.1 全文总结... 105

7.2 未来工作展望... 108

参考文献... 109

致谢... 123

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    124