热带太平洋冷舌模态及其对ENSO的影响

发布时间：2018-04-30 16:16

本文选题：热带太平洋 + 长期趋势　；参考：《兰州大学》2016年博士论文

【摘要】：热带太平洋冷舌模态(CTM)是热带太平洋海表温度异常(SSTA)的EOF第二模态,代表了热带太平洋冷舌区的海温和冷舌区之外的反位相的变化。当CTM为正位相时,热带太平洋冷舌区为冷SSTA,而冷舌区之外的其他区域为暖SSTA,负位相情况相反。CTM的时间序列(NPC2)主要为长期冷趋势并且与全球变暖有很高的相关,其在1930年之前基本上为负位相,1940年到1980年之间为年际振荡,1980年之后基本上为正位相。与此同时,CTM与大气场和次表层海温紧密联系,是一个海气耦合的模态。本文以热带太平洋海温长期趋势的观测事实为依据,证实了CTM是一个真实的物理模态。系统地建立了CTM的海洋内部动力过程并探讨了它与全球变暖的关系。提出了CTM作为背景场调节ENSO温跃层反馈的物理机制。评估了CMIP5模式的历史(historical)试验对CTM的模拟能力。研究了CMIP5工业革命之前(piControl)试验中无全球变暖强迫下CTM的年际变化特征及相应的物理过程,进一步证实了无全球变暖强迫下,CTM依然是一个真实的物理模态。主要结论如下:(1)热带太平洋冷舌模态及其在全球变暖背景下的动力过程在全球变暖背景下,CTM能很好的表征热带太平洋的背景场,是一个真实的物理模态,这在多套海表温度资料和次表层海温资料当中都能得到证明。若去除ENSO信号干扰后,在多套资料当中都能得到赤道东太平洋海温长期冷趋势和西太平洋暖趋势。CTM为一个海气耦合模态,其长期冷趋势是海洋动力过程对全球变暖的响应。本文针对过去海洋内部动力反馈过程的研究不足,从热收支方程出发,系统地建立了全球变暖背景下CTM的海洋内部动力过程。利用赤道东太平洋的海温热收支方程,发现了净热通量对CTM起了阻尼作用,而四个海流平流项(-u′?t?x,-v?t′?y,-w?t′?z,和-w′?t?z)影响着ctm的海温变化。在它们之中,气候态上翻流对应的垂直平流项(-w?t′?z)是引起ctm长期冷趋势最重要的因子。另外,-w?t′?z平流项的长期冷趋势主要受控于全球变暖背景下减小的垂直海温异常梯度(?t′?z)。而其他三项对ctm长期冷趋势的贡献较小。(2)在全球变暖背景下热带太平洋冷舌模态对enso的影响从ctm作为全球变暖背景下热带太平洋海温背景场的角度,提出了全球变暖背景下ctm调节enso温跃层反馈的物理机制。研究发现,当强的正ctm叠加于elni?o时,ctm在赤道东太平洋的冷ssta使得elni?o在该区域的ssta变弱,进一步引起elni?o的暖中心沿着赤道向西偏移,这与近期中部型elni?o的频发有紧密的联系。另外,强的正ctm的暖ssta导致elni?o在赤道东太平洋之外的ssta变暖,进一步引起赤道西太平洋和赤道外的ssta变暖,从而导致elni?o的经向和纬向宽度变宽。反之,当强的正ctm叠加于lani?a时,ctm在赤道东太平洋的冷ssta使得lani?a的冷ssta在该区域增强。而lani?a的ssta中心不变,依然位于赤道东太平洋。同时,ctm在赤道东太平洋之外的暖ssta使得lani?a在赤道西太平洋和赤道外的ssta变暖,从而引起lani?a的经向和纬向宽度变窄。以上现象是由于赤道太平洋冷舌区和冷舌区之外的海温对全球变暖不同的响应所引起。基于结论(1)的研究,即对ctm的长期冷趋势起主要贡献的为-w?t′?z平流项,这对应enso理论中的温跃层反馈过程。因此,当强的正ctm叠加于elni?o上时,将会抑制赤道东太平洋地区的温跃层反馈,使得该区域elni?o的强度减弱。而当强的正ctm叠加于lani?a上时,它会加强赤道东太平洋的温跃层反馈,使得该区域lani?a的强度增强。并且,在充电-放电enso模型中,加入了ctm对应的长期冷趋势,验证了这一观点。(3)在cmip5历史实验中模式对冷舌模态的模拟利用20个cmip5模式评估了历史试验下模式对enso和ctm时空特征的模拟能力。其中有5个模式(cesm1-cam5,cmcc-cm,fgoals-g2,ipsl-cm5b-lr,noresm1-m)基本上能模拟出enso中心位置和马蹄形ssta空间特征以及2到7年年际振荡特征,还有CTM热带太平洋冷舌区和冷舌区之外SSTA反位相变化以及CTM主要的长期冷趋势。另外,这5个模式对赤道东太平洋冷舌区海温对全球变暖响应模拟较好。即在全球变暖背景下,这5个模式对应的赤道东太平洋垂直海温梯度(?T′?z)变冷,在气候态上翻流作用下,产生冷平流项(-w?T′?z),最终引起CTM的长期变冷趋势。(4)在CMIP5工业革命之前试验中冷舌模态的年际变化在piControl试验下,分析了CTM的年际变化及其物理机制,证实了无全球变暖强迫下,CTM依然是一个真实的物理模态。研究表明在该试验中ENSO和CTM的年际变化通过赤道东传Kelvin波和Bjerknes反馈,使二者有紧密的物理联系,联系为:El Ni?o→CTM→La Ni?a→-CTM→El Ni?o,其中→代表从原因到结果。与此同时,尽管在观测中CTM的年际信号被其长期趋势所掩盖,但依然有年际变化,如1940年到1980年CTM主要为年际振荡。在观测中El Ni?o→CTM或La Ni?a→-CTM的过程与模式一致,但是CTM→La Ni?a或-CTM→El Ni?o这一过程通不过显著性检验,并且观测中因El Ni?o衰亡引起的赤道东太平洋冷海温强度与模式相比较弱,这可能是由于观测中CTM受全球变暖的强迫引起长期冷趋势太强而年际信号太弱。
[Abstract]:The tropical Pacific cold tongue mode (CTM) is the EOF second mode of the tropical Pacific sea surface temperature anomaly (SSTA), representing the change of the reverse phase in the cold tongue region of the tropical Pacific. When CTM is a positive phase, the cold tongue region of the tropical Pacific is cold SSTA, while the other regions outside the cold tongue region are warm SSTA, and the negative phase is opposite.C. The time series (NPC2) of TM is mainly a long-term cold trend and has a high correlation with global warming. It is basically negative phase before 1930, the interannual oscillation between 1940 and 1980, and basically positive phase after 1980. At the same time, CTM is closely connected with the gas field and subsurface sea surface temperature. This paper is a modal of sea air coupling. Based on the observational facts of the long-term trend of tropical Pacific SST, it is proved that CTM is a real physical mode. The internal dynamic process of CTM is established and the relationship between it and global warming is discussed. The physical mechanism of CTM as the background field to regulate the ENSO thermocline feedback is proposed. The history of the CMIP5 model is evaluated (historica). L) the simulation ability of the test for CTM. The interannual variation and physical process of CTM without global warming forced before the CMIP5 Industrial Revolution (piControl) test are studied. It is further confirmed that CTM is still a real physical mode without global warming coercion. The main conclusions are as follows: (1) the cold tongue mode of the tropical Pacific and its whole In the background of global warming, under the background of global warming, CTM can characterize the background field of the tropical Pacific very well. It is a real physical mode, which can be proved in many sets of sea surface temperature data and subsurface sea surface temperature data. If ENSO signal interference is removed, the eastern equatorial Pacific can be obtained in many sets of data. The long-term cold trend of SST and the Western Pacific warm trend.CTM is a sea air coupling mode, and its long-term cold trend is the response of the ocean dynamic process to global warming. In this paper, in view of the lack of research on the dynamic feedback process in the past, the internal dynamic process of CTM under the background of global warming is systematically established from the heat budget equation. Using the sea temperature heat budget equation in the equatorial east Pacific, it is found that the net heat flux has a damping effect on CTM, and the four current advection terms (-u '? T? X, -v? T'? Y, -w? T '? Z, and -w' t?) affect the sea temperature change. In them, the vertical advection corresponding to the climate state is the most important of the long-term cold trend. In addition, the long-term cold trend of the -w? T '? Z advection term is mainly controlled by the reduced vertical sea temperature anomaly gradient (? T'? Z) under the background of global warming. And the other three items have little contribution to the long-term cold trend of CTM. (2) the influence of the cold tongue mode on the ENSO in the tropical Pacific under global warming background is from CTM as a global warming tropical Taiping. The physical mechanism of CTM regulation of ENSO thermocline feedback under the background of global warming is proposed. When the strong positive CTM is superimposed on Elni? O, the cold SSTA of CTM in the eastern equatorial Pacific makes Elni o weaker in the SSTA of the region and further causes Elni o warm center to move westward along the equator, which is in the middle of the near future. The frequent occurrence of type Elni? O is closely related. In addition, the warm SSTA of the strong positive CTM leads to the warming of Elni? O outside the equatorial eastern Pacific, which further causes the SSTA in the equatorial western Pacific and the equatorial SSTA to be warmer, leading to the widening of the meridional and latitudinal width of Elni o. Sta makes the cold SSTA of the Lani? A enhanced in the region. And the SSTA center of LaNi a remains unchanged in the equatorial east Pacific. At the same time, the warm SSTA outside the equatorial east Pacific causes Lani a to become warmer in the western equatorial Pacific and equatorial Pacific, which causes the meridional and zonal width to narrow. The above phenomenon is due to the cold equatorial Pacific. The study on the response of the sea temperature outside the tongue area and the cold tongue region to the global warming. Based on the conclusion (1), the -w? T '? Z advection is the main contribution to the long-term cold trend of CTM, which corresponds to the thermocline feedback process in the ENSO theory. Therefore, when the strong positive CTM is superimposed on the Elni? O, the temperature of the eastern equatorial Pacific will be suppressed. The jump layer feedback makes the intensity of the Elni o in the region weakened. And when the strong positive CTM is superimposed on Lani? A, it will strengthen the thermocline feedback in the eastern equatorial Pacific and enhance the intensity of the Lani? A in this region. And, in the charge discharge ENSO model, the long cold trend corresponding to CTM is added to verify this view. (3) in cmip5 history experiment Model simulation of cold tongue mode uses 20 cmip5 models to evaluate the simulation ability of ENSO and CTM spatiotemporal characteristics under historical experiments. Among them, 5 modes (cesm1-cam5, cmcc-cm, fgoals-g2, ipsl-cm5b-lr, noresm1-m) can basically simulate the ENSO center position and the spatial characteristics of the horseshoe SSTA and the characteristics of the interannual oscillation of 2 to 7 years, as well as the characteristics of the interannual oscillation of 2 to 7 years. The reverse phase changes of SSTA in the cold tongue region and cold tongue region of the tropical Pacific CTM and the main long-term cold trend of CTM. In addition, the response of the 5 models to the global warming in the cold tongue region of the equatorial east Pacific is better. That is, the vertical sea temperature gradient (? T '? Z) of the equatorial east Pacific Ocean (? T'? Z) is cooled in the climate under the background of global warming. Under the action of upflow, the cold advection term (-w? T '? Z) will eventually lead to the long-term cold trend of the CTM. (4) the interannual variation of the cold tongue mode in the experiment before the CMIP5 industrial revolution is under the piControl test, and the interannual variation and physical mechanism of the CTM are analyzed. It is confirmed that CTM is still a real physical mode without global warming coercion. The results show that the interannual variation of ENSO and CTM in this experiment is based on the feedback from the equatorial Eastward Transmission of Kelvin wave and Bjerknes, which makes the two people have close physical connections, which are as follows: El Ni? O, CTM, La Ni, a, -CTM, and results. There are interannual variations, such as the interannual oscillation of CTM from 1940 to 1980. In observation, the process of El Ni? O to CTM or La Ni? A to -CTM is consistent with the model, but CTM > La Ni? It may be due to the fact that CTM is forced by global warming to cause long-term cold trend and the interannual signal is too weak.

【学位授予单位】：兰州大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P732

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