2000年前后两类ENSO属性年代际变化的动力学研究

发布时间：2018-03-02 14:03

本文选题：年代际变化　切入点：两类ENSO　出处：《中国气象科学研究院》2017年硕士论文　论文类型：学位论文

【摘要】：El Ni?o和南方涛动(合成ENSO)在2000年前后发生了显著的年代际变化,使得ENSO的特征发生了明显改变:与1980-1999年相比,2000年以后ENSO的振幅减弱,主周期缩短,中太平洋型(CP型)El Ni?o事件出现的频率升高,且没有典型的东太平洋型(EP型)El Ni?o事件出现,ENSO的预报技巧也显著降低。本文利用再分析资料,基于统计和诊断方法,详细分析了这次年代际变化相关的特征变化和动力学诊断变化,并考察了造成这次ENSO年代际变化的可能原因。ENSO属性的显著变化,包括振幅、频率和空间型等,与两类ENSO的变化有关,并与两个ENSO耦合模态相联系,即准四年模态(QQ模态)和准两年模态(QB模态),其实质是两个ENSO模态的相对活跃性发生了改变:在1980-1999年期间,与EP型ENSO相联系的QQ模态和与CP型ENSO相联系的QB模态共存于热带太平洋地区,但QQ模态的强度明显高于QB模态,ENSO以EP型为主。但在2000年之后,QQ模态的强度显著减弱,而QB模态则成为热带太平洋地区的主要年际模态,ENSO也以CP型为主。由于2000年前后的年代际变化,使影响ENSO增长和位相转换的主要海洋反馈过程也发生了明显改变,并影响了两个模态的活跃性。QQ模态是一个典型的“充电振子”模态,其位相转换的主要机制来自于赤道热容量缓慢的海洋性动力调整即温跃层反馈(TH项),而QB模态的位相转换机制则来自于纬向平流反馈(ZA项)。反馈过程的改变使得两个ENSO模态的活跃性发生了改变:QQ模态的TH项明显减弱,对ENSO位相转换的作用也明显减小,使得QQ模态活跃性降低,而QB模态的ZA项则明显增强更有利于QB模态的发展。除此以外,Ekman反馈则主要影响赤道太平洋120°W以东的地区,且2000年之后明显不利于ENSO的发展。热带太平洋地区气候平均态的改变可能是这次年代际变化的原因。在2000年以后,赤道东太平洋表面平均信风明显减弱,而在赤道中西太平洋,温跃层明显加深,纬向信风也有所增强,这些平均态的改变可能导致了TH项和ZA项的变化,进而使QQ模态减弱,QB模态增强。全面深入的归因分析还有待进一步的研究。
[Abstract]:El Ni? O and the Southern Oscillation (synthetic ENSO) showed significant Interdecadal changes before and after 2000, resulting in a significant change in the characteristics of ENSO: compared with 1980-1999, the amplitude of ENSO decreased after 2000, and the main period shortened. O increased frequency of incidents and absence of typical EP-type EP-type El Ni? O the prediction technique of ENSO is also significantly reduced. Based on the statistical and diagnostic methods, the characteristics and dynamic diagnostic changes related to the Interdecadal variation are analyzed in detail by means of reanalysis data in this paper. The possible causes of this ENSO decadal variation, including amplitude, frequency and spatial pattern, are investigated, which are related to the changes of two ENSO types, and are associated with two ENSO coupling modes. In essence, the relative activity of the two ENSO modes has changed: in 1980-1999, The QQ mode associated with EP ENSO and the QB mode associated with CP type ENSO coexist in the tropical Pacific region, but the intensity of QQ mode is obviously higher than that of EP mode, but the intensity of QQ mode decreases significantly after 2000. However, QB mode has become the main interannual mode in the tropical Pacific. Due to the decadal changes before and after 2000, the main ocean feedback processes that affect the growth and phase transition of ENSO have also changed obviously. And affected the activity of the two modes. QQ mode is a typical "charging oscillator" mode, The main mechanism of phase transition comes from the slow oceanic dynamic adjustment of the equatorial thermal capacity, that is, the thermocline feedback of th term, while the QB mode of the phase conversion mechanism comes from the za term of the zonal advection feedback. The change of the feedback process results in the change of the feedback process. The activity of the two ENSO modes has changed and the th term of the two ENSO modes has been significantly weakened. The effect on the phase transition of ENSO is also obviously reduced, and the activity of QQ mode is decreased, and the ZA term of QB mode is obviously enhanced. In addition, the Ekman feedback mainly affects the area east of 120掳 W in the equatorial Pacific Ocean. After 2000, the change of climate average state in the tropical Pacific may be the reason for this interdecadal change. After 2000, the average trade wind on the surface of the equatorial eastern Pacific significantly weakened, but in the equatorial and western Pacific, The thermocline is obviously deepened, and the zonal trade wind is also strengthened. The changes of these mean states may lead to the changes of th and ZA terms, which further weaken the QB mode of QQ. The comprehensive and in-depth attribution analysis still needs further study.
【学位授予单位】：中国气象科学研究院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P732

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