兰州大学机构库 >大气科学学院
两类ENSO事件对中国东部降水影响研究
Alternative TitleThe research on the Impact of Two Types of ENSO Evnets on Precipitation in Eastern China
马百胜
Thesis Advisor李艳
2019-05-01
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name硕士
Degree Discipline气象学
Keyword东部型ENSO 中部型ENSO 极端降水 Hadley环流 PJ波列
Abstract中国东部地处东亚季风区,其降水异常不仅对工农业生产、社会基础设施建设产生重要影响,也会威胁人民生命财产安全。ENSO(El Niño-Southern Oscillation)作为热带海-气耦合系统年际变化中的最强信号,可以对该地区的降水产生重要影响。因此研究ENSO对于我国东部地区降水的影响对于该地区降水预测具有科学和现实意义。本文使用1979-2010年中国逐日降水格点数据(CN05.1)、全球海温数据和气象再分析资料,系统地分析了东部型和中部型ENSO发生时,热带太平洋海温的异常分布特征及Hadley环流的异常响应;两类ENSO对中国东部地区降水的影响特征及其影响机理;1979-2010年两次最强中部型El Niño/La Niña事件对中国东部降水的影响以及与一般ENSO事件的差异;最后从大气环流和波作用通量(Wave Action Flux,简称WAF)的角度分析了最强事件对中国东部降水的影响机制,主要结论如下:(1)东部型El Niño/La Niña发生时,热带太平洋海温异常在纬向呈现出偶极子振荡,在经向表现为关于赤道对称的结构;中部型El Niño/La Niña发生时,热带太平洋海温异常在纬向为三极分布特征,经向在秋冬季关于赤道对称,而在春夏季则关于赤道非对称。此外,两类El Niño/La Niña对Hadley环流也具有不同的影响,东部型El Niño/La Niña发生时,Hadley环流异常在四季均保持关于赤道对称的结构特征,而当中部型El Niño/La Niña发生时,在秋、冬两季Hadley环流异常关于赤道对称,但在春、夏季节则关于赤道非对称,这与两类El Niño/La Niña事件发生时海温的经向结构特征是相吻合的,表明海温的异常强迫对大气环流具有显著的影响。(2)在各个发展阶段,两类El Niño/La Niña对中国东部降水的影响都有较大不同。在东部型El Niño的冬季成熟期,中国东南地区降水偏多而中部和东北地区降水偏少;在其春季衰退期,中国东部大部分地区降水偏多;在夏季衰退期,降水区域主要存在于长江中下游流域和东北地区。当中部型El Niño发生时,中国东部雨带的位置要较东部型El Niño偏北,在春季衰退期,中国华南降水偏少而长江流域降水偏多;在夏季衰退期,雨带主要集中在黄-淮流域,长江以南地区则干旱。两类La Niña对中国东部降水的影响与El Niño基本相反。本文进一步从大气环流的角度分析了两类El Niño/La Niña对中国东部降水影响的机理,结果表明,东部型El Niño发生时,赤道西太平洋有正的位势高度异常,副高偏强,菲律宾海存在异常反气旋环流,其西北侧西南气流把太平洋水汽输送到中国东部,结合副高以及水汽辐合带的季节性移动,可导致中国东部降水在各季节中的异常。中部型El Niño发生时,由于赤道太平洋地区海温异常模态与东部型事件不同,所以导致的大气环流异常也不相同,总体表现为副高和反气旋的位置较东部型偏西偏北。此外,中部型El Niño事件引起的PJ波列(Pacific-Japan wave train,简称PJ wave train)较东部型强度偏弱,位置偏东,这是中部型事件对中国东部降水的影响较东部型事件偏弱的重要原因。两类La Niña事件发生时,海温异常结构与相应的El Niño事件相反,所以引起的中国东部降水异常也与后者相反。此外,在各季节中,中国东部地区累计极端降水量从西北至东南递增,且累计极端降水占总降水较大比重。当东部型和中部型El Niño/La Niña发生时,中国东部地区极端降水异常百分率的空间分布特征与总降水保持一致,而弱降水的异常分布则变化不明显,所以两类El Niño/La Niña对中国东部极端降水的影响较弱降水更加显著,且极端降水异常对总降水异常的贡献更大。(3)挑选出1979-2010年两次最强的中部型El Niño/La Niña事件,分别为2009/10年El Niño事件和1998/99年La Niña事件,分析它们对中国东部降水的影响。在最强中部型El Niño的成熟期,中国西南地区为负的降水异常,而在东部和北部地区降水则偏多,这与一般中部型El Niño有所差异;在最强中部型La Niña的成熟期,中国东部大部分地区均为负的降水异常,而对于一般中部型La Niña事件,在长江以北地区降水却偏多,表现出与最强事件不同的分布特征。然而,在最强中部型El Niño/La Niña的衰退期,中国东部降水异常分布特征则与一般中部型事件相似,但强度表现更强。在最强中部型El Niño发生时,异常反气旋和副高均较一般事件偏强,且副高的位置也更加偏西偏北;在最强中部型La Niña发生时,异常气旋性环流较一般事件更强,副高也东撤南退的更明显,所以最强事件对中国东部降水的影响较一般事件偏强。另外,在最强中部型El Niño的成熟期,由于中国东部大部分地区被气旋性环流控制,这促使水汽可以被输送到中国北方地区,故而使得2009年冬季中国东部地区降水异常与一般中部型El Niño事件不同;在最强中部型La Niña的成熟期,中国东部大部分地区射出长波辐射(Outgoing Longwave Radiation,简称OLR)为正距平,对流活动受到抑制,不利于该地区降水的发生,这与一般事件也不相同。强烈的对流活动会激发出定常波,所以在对流活动较强的区域波作用通量也更强,在最强El Niño的夏季衰退期,有明显的WAF从赤道地区向北传播至华南等地,并伴随着PJ波列的传播;在最强La Niña发生时,由于西太平洋地区对流活动一直偏强,相应的有明显的WAF从东南亚地区向北传播。
Other AbstractEastern China is located in the East Asian monsoon region.  The abnormal pre-cipitation in eastern China not only has an important impact on industrial and agricultural production and social infrastructure construction, but also threatens the safety of people's lives and property. As the strongest signal in the inter-annual variation of tropical sea-air coupling system, ENSO has an important effect on the precipitation in eastern China. Therefore, studying the impact of ENSO on the precipitation in eastern China has scientific and practical significance for precipitation prediction over this region. Using the Daily Precipitation Grid Data (CN05.1) in China, Global Sea Surface Temperature Data, and Meteorological Reanalysis Data  from 1979 to 2010, the paper systematically analyzes the abnormal distribution characteristics of tropical Pacific sea surface temperature (SST) and the abnormal response of Hadley circulation when the Eastern-Pacific ENSO (EP ENSO) and Central-Pacific ENSO (CP ENSO) occur. The influence characteristics of two types of ENSO on the precipitation in eastern China is also analyzed as well as its influencing mechanism. Meanwhile, the effects of the two strongest CP El Niño/La Niña events from 1979 to 2010 are selected and their different impact on precipitation in eastern China are explored from the general events. Finally, from the perspective of atmospheric circulation and Wave Action Flux (WAF), the influence mechanism of the strongest El Niño/La Niña events on precipitation in eastern China is analyzed. The main conclusions are as follows:(1) When the EP El Niño/La Niña occurs, the tropical Pacific SST anomaly exhibits dipole oscillation in the latitudinal direction and a equator symmetrical structure in the meridional direction. When the CP El Niño/La Niña occurs, the tropical Pacific SST anomaly is characterized by tripolar distribution in the latitudinal direction; while in the meridional direction, the SST anomaly is a equator symmetrical structure in autumn and winter, but asymmetric about the equator in spring and summer. Because of the different structures of the tropical Pacific SST anomalies when the two types of El Niño/La Niña occur, there are different effects on the Hadley circulation. When the EP El Niño/La Niña occurs, the Hadley Circulation anomaly maintains the characteristics of equator symmetry in the whole year. When the CP El Niño/La Niña occurs, the Hadley Circulation anomaly is symmetrical about the equator in autumn and winter, but asymmetric in the spring and summer. This is consistent with the meridional structural characteristics of the SST anomaly when two types of El Niño/La Niña events occur, indicating that the abnormal forcing of SST has a significant impact on atmospheric circulation. (2) At all stages of the two types of El Niño/La Niña, their effects on precipitation in eastern China are quite different. During the mature period of EP El Niño in winter, precipitation in southeastern China is relatively high and precipitation in central and northeastern regions is less. During its decayed period in spring, rainfall is excessive in most areas of Eastern China. During its decayed period in summer, the precipitation area mainly exists in the middle and lower reaches of the Yangtze River basin and the northeastern region of China. When the CP El Niño occurs, the location of rain belt in eastern China is northward than that in EP El Niño, while during the period of maturity in spring, less precipitation in South China and more precipitation in the Yangtze River Basin. During the period of maturity in summer, rainfall belts are mainly concentrated in the Huang-Huai River Basin, while drought occurs in the south of the Yangtze River. The effect of two types of La Niña on precipitation in eastern China is basically opposite to that of the corresponding El Niño events. In this paper, the mechanism of two types of El Niño/La Niña affecting precipitation in eastern China is analyzed from the perspective of atmospheric circulation. The result  shows when the EP El Niño occur, the atmospheric circulation is characterized as a positive geopotential height anomaly in the equatorial Western Pacific, the stronger Western Pacific Subtropical High (WPSH) , and an abnormal anti-cyclone circulation exists in the Philippine Sea. The southwester transports moisture from Pacific to eastern China, combined with the seasonal movement of WPSH and moisture convergence zone, which can lead to the seasonal variation of the precipitation in eastern China. In the case of the CP El Niño incident, the atmospheric circulation anomalies are different due to the difference of the SST anomaly distribution in the equatorial Pacific region between CP El Niño and EP El Niño, the overall performance is that the position of the WPSH and the anti-cyclone circulation is further north than that during the EP El Niño. In addition, the Pacific-Japan wave train  (PJ wave train) caused by the CP El Niño event is weaker than that by the EP El Niño and is located eastward, which may be the reason that the CP El Niño has a weaker impact on the precipitation in eastern China than that of the EP El Niño. When two types of La Niña events occur, the abnormal structure of SST is opposite to that of the corresponding El Niño events, so the precipitation anomaly in eastern China is also opposite to the latter. In addition, the cumulative extreme precipitation in eastern China is increasing from northwest to southeast, and the cumulative extreme precipitation accounts for a large proportion of total precipitation in each season. When the EP and CP El Niño/La Niña occurs, the spatial distribution characteristics of the extreme precipitation anomalies in eastern China are consistent with the total precipitation, but the abnormal distribution of weak precipitation does not change significantly. Therefore, the two types of El Niño/La Niña mainly affect the anomalous distribution of total precipitation by affecting the extreme precipitation anomalies in eastern China. (3) The paper selects the El Niño event in 2009/10 and La Niña event in 1998/99 as the two strongest CP El Niño/La Niña events from 1979 to 2010, and analyzes their influence on the precipitation in eastern China. During the maturation period of the strongest CP El Niño, the precipitation anomaly is negative in southwest China, but positive in East and North China, which is different from that in the general CP El Niño. During the maturation period of the strongest CP La Niña, the precipitation in most parts of eastern China are uniformly less. While the north of the Yangtze River has more precipitation in the general CP La Niña events, showing different distribution characteristics from the strongest events. In the decayed period, the influencing characteristics on precipitation in eastern China are similar to that in the general CP El Niño/La Niña events, but with a stronger intensity. When the strongest CP El Niño occurs, the anomalous anticyclone circulation and WPSH are stronger than the general events, and the WPSH is located more westerly and northerly. When the strongest CP La Niña occurs, the anomalous cyclonic circulation is stronger than the general event, and the WPSH eastward retreat more obvious, so the impact of the strongest events on the precipitation in eastern China is stronger than that of general events. In addition, during the maturation period of the strongest CP El Niño, moisture can be transported to northern China because most of eastern China is controlled by cyclonic circulation. Therefore, the precipitation anomaly in eastern China in winter of 2009 is different from the general CP El Niño events. During the maturation period of the strongest CP La Niña, the Outgoing Longwave Radiation (OLR) is positive anomaly in most areas of eastern China, indicating the convective activity is inhibited, which is not conducive to precipitation occurrence in this area, which is different from that of the general events. The strong convection will stimulate stationary waves and the WAF is stronger in regions with stronger convective activity. During the decayed period of the strongest El Niño in summer, there is a clear spread of WAF from the equatorial region to the south of China, accompanied by the spread of PJ wave trains. When the strongest CP La Niña occurs, due to the strong convective activity in the western Pacific, there is a clear WAF spreading northward from Southeast Asia.
Pages77
URL查看原文
Language中文
Document Type学位论文
Identifierhttp://ir.lzu.edu.cn/handle/262010/338312
Collection大气科学学院
Affiliation大气科学学院
Recommended Citation
GB/T 7714
马百胜. 两类ENSO事件对中国东部降水影响研究[D]. 兰州. 兰州大学,2019.
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