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1.
利用1961—2008年陕西78个气象站夏季 (6—8月) 降水资料、NCEP/NCAR位势高度场和风场月平均再分析资料,采用合成及相关分析方法探讨ENSO发展和衰减阶段对陕西夏季降水异常的影响,以期为陕西夏季降水的气候预测提供线索和依据。结果表明:陕西夏季降水异常对ENSO发展和衰减阶段的响应存在显著差异,El Ni?o发展阶段和La Ni?a衰减阶段,陕西夏季降水偏少; El Ni?o衰减阶段和La Ni?a发展阶段,陕西夏季降水偏多; ENSO不同阶段对陕西7月降水影响最为显著。比较而言,El Ni?o事件对陕西夏季降水的影响更加显著。在El Ni?o衰减、La Ni?a发展阶段,西太平洋副热带高压偏强、偏西,东亚夏季风偏弱,而在El Ni?o发展、La Ni?a衰减阶段,西太平洋副热带高压偏弱、偏东,东亚夏季风偏强,El Ni?o过程对东亚夏季风强弱的影响更加显著。ENSO发展和衰减阶段通过影响大气环流变化和东亚夏季风的强弱,进而影响陕西夏季降水。 相似文献
2.
两类ENSO背景下中国东部夏季降水的环流特征及关键系统 总被引：1，自引：0，他引：1
利用全国160站逐月降水资料、74项环流指数、HadISST月平均海温资料以及NCEP/NCAR月平均再分析资料,对比分析了两类ENSO事件衰减阶段中国东部夏季降水及相应大气环流的差异,并探讨其可能成因。结果表明:1)EP型El Ni?o(La Ni?a)事件次年夏季,中国东部降水由北至南呈正负正(负正负)的三极型反相分布;CP型El Ni?o(La Ni?a)事件次年夏季,中国东部降水由北至南呈正负(负正)的偶极型反相分布;2)El Ni?o事件次年夏季,西北太平洋副热带高压(以下简称西太副高)及南亚高压均偏强,EP型西太副高偏西、南亚高压偏东,CP型西太副高范围更大、强度更强;La Ni?a事件次年夏季,西太副高及南亚高压强度偏弱,CP型强于EP型但弱于气候平均;3)El Ni?o事件期间西北太平洋上存在异常反气旋,EP型位置偏南,强度更强,持续时间更长,CP型位置偏北,范围更大;La Ni?a事件期间,西北太平洋区域至中国东南部存在异常气旋,EP型异常气旋的强度及范围均不及CP型;4)两类El Ni?o事件期间异常反气旋的差异可能与印度洋海盆增暖及太平洋海温持续性偏冷有关;两类La Ni?a事件期间异常气旋的差异可能由赤道西太平洋海温持续偏暖造成。 相似文献
3.
《大气和海洋科学快报》2017,(2)
合成分析了La Ni?a年东亚夏季风和东亚夏季降水的季节内变化。结果表明,La Ni?a年夏季暖池对流偏强,西太平洋出现异常气旋,西太平洋副高偏向东北。这种异常型随季节进程有明显变化,7月异常达到最大。La Ni?a年东亚降水呈纬向型分布,中国东部降水偏少,西太平洋海面降水偏多。与此相比,El Ni?o年降水呈经向型分布,热带降水偏少,副热带和中纬度降水偏多。因此,不能简单将La Ni?a的影响认为是El Ni?o的反对称。 相似文献
4.
准两年振荡及其对东亚大气环流和气候的影响 总被引：13，自引：6，他引：13
通过多年资料分析,本文研究了平流层准两年振荡(QBO)的演变特征及其对东亚及西太平洋地区大气环流和气候变化的影响.结果表明,平流层QBO的演变特征是:东风向西风转换最早出现在印度洋赤道地区;西风向东风转换最早出现在美洲和西太平洋赤道地区.中国东部降水量、气温以及西太平洋副高和东亚急流都有准两年周期变化,并同平流层QBO有密切关系;平流层QBO对西太平洋台风活动也有一定影响,QBO的西风位相期西太平洋台风偏少.另外,ENSO对于平流层QBO有明显影响,一般在ENSO发生之后,QBO的西风位相期持续时间缩短. 相似文献
5.
ENSO位相转换对华北雨季降水的影响 总被引：7，自引：2，他引：5
利用国家气候中心华北地区站点雨季降水数据及美国国家环境预报中心和大气研究中心（NCEP/NCAR）的再分析数据等资料,采用统计诊断方法,分析了1961~2014年华北雨季降水异常偏多（少）年对应的Ni?o3.4指数变化特征,发现华北雨季降水异常偏多年通常发生在El Ni?o结束且当年转为La Ni?a的年份,而华北雨季降水异常偏少年通常发生在赤道中东太平洋冷水位相结束且当年发展成El Ni?o事件的年份。并且在华北雨季降水异常偏多年,7~8月华北平均日降水量超过10 mm的天数约占25%,日降水量在4~10 mm的天数也约占25%,两者所占比率远高于华北雨季降水异常偏少年。对华北雨季降水异常偏多年的同期环流特征分析显示:西北太平洋副热带高压（副高）北跳偏早且有明显阶段性偏北情况,同时东亚高空副热带西风急流北移,从而造成华北雨季天气过程频繁、降水偏多。进一步诊断环流特征与ENSO位相转换的关系发现:相比El Ni?o衰减年,在El Ni?o转为La Ni?a的年份,7~8月500 hPa日本海到渤海正位势高度距平加强,更符合华北雨季降水偏多年的典型环流特征;同时热带沃克环流显著加强,造成东亚高空副热带西风急流北移更为显著,从而更有利于华北盛夏和雨季降水偏多。文中揭示的现象启示我们在做华北盛夏降水和雨季降水的预测时,需要关注ENSO事件前期的变化速度以及未来的演变特征。 相似文献
6.
两个典型ENSO季节演变模态及其与我国东部降水的联系 总被引：2，自引：0，他引：2
本文根据1950~2014年月平均海温和大气环流资料以及中国160站降水等资料,利用扩展经验正交函数（EEOF）分析、相关分析以及合成分析等方法,分析了太平洋海温季节演变的主导模态,并探讨了各模态与中国东部降水和东亚环流季节变异的关系及其联系的物理过程。结果表明,ENSO（El Ni?o/Southern Oscillation）季节演变存在2个主导模态,包含4种类型:El Ni?o持续型、La Ni?a持续型、La Ni?a转El Ni?o型和El Ni?o转La Ni?a型。发现不同模态和类型的ENSO季节变化过程我国东部降水距平的分布和强度都有明显差异。El Ni?o持续型和El Ni?o转La Ni?a型,冬春季和初夏均处在El Ni?o背景下,降水异常分布存在一定共性,但盛夏和秋季分别受El Ni?o和La Ni?a影响,降水异常分布差异十分明显,前者雨带北跳慢、位置偏南而后者雨带北跳快、位置偏北。La Ni?a持续型和La Ni?a转El Ni?o型也是如此,冬春季和初夏降水异常分布大致相似,但盛夏和秋季分别受La Ni?a和El Ni?o影响,前者雨带北跳快、位置偏北而后者雨带北跳慢、位置偏南。因此,利用ENSO做我国降水的气候预测时,不能只着眼于前期冬季El Ni?o或La Ni?a事件,还应考虑其未来演变所属的可能模态和类型。对他们之间联系的物理过程分析表明,不同ENSO季节演变模态和类型主要通过影响西太平洋副热带高压以及西风带经向型/纬向型环流调整及伴随的低纬暖湿水汽输送以及中高纬冷空气活动变化来影响我国东部降水。其中,西太平洋菲律宾群岛附近异常反气旋（或气旋）、赤道Walker环流和北半球Hadley环流分别是联系ENSO与西太平洋副热带高压活动和东亚西风带经向型/纬向型环流的重要环节。 相似文献
7.
ENSO发展和衰减阶段对云南夏季降水的影响研究 总被引：6，自引：0，他引：6
利用NCEP提供的大气再分析资料和云南122站降水资料分析了ENSO发展和衰减阶段对云南夏季降水异常的影响。结果发现：云南夏季降水异常分布对ENSO发展和衰减阶段的响应存在明显差异。处在发展阶段的El Ni?o事件会导致云南夏季大部分区域降水偏少;处在衰减阶段的El Ni?o事件会导致云南夏季降水呈现东少西多的分布;处在发展阶段的La Ni?a事件发会造成云南夏季大部分区域降水偏多,并且云南夏季降水异常对该阶段的响应最明显;处在衰减阶段的La Ni?a事件会造成云南夏季大部分区域降水偏少。通过合成分析发现：ENSO的发展和衰减阶段对夏季低纬度大气环流的影响存在显著差异,特别是对副热带高压和夏季风强弱的影响显著不同,从而导致云南夏季降水异常。值得一提的是,La Ni?a事件的发展阶段可作为影响云南夏季降水的一个强信号因子,应在短期气候预测中加以考虑。 相似文献
8.
根据El Ni?o和La Ni?a发生以后冬季赤道东太平洋海温距平的月际差定义了El Ni?o和La Ni?a冬季增强型和冬季减弱型, 讨论了El Ni?o和La Ni?a冬季增强型和减弱型冬、春、夏季大气环流、东亚季风及我国夏季降水和旱涝分布的特征.我国夏季降水和旱涝有明显差异的四种不同分布型可能与冬季所处ENSO循环的不同阶段以及大气环流和东亚季风对它的不同响应有关.提出了从El Ni?o和La Ni?a冬季不同型→大气环流和东亚季风→我国夏季降水和旱涝分布型的物理统计概念模型. 相似文献
9.
根据观测资料的研究指出春季北极涛动(Arctic Oscillation, AO)对随后冬季厄尔尼诺-南方涛动(El Nino–Southern Oscillation, ENSO)的影响具有明显不对称性。春季AO处于正位相时,它对随后冬季厄尔尼诺(El Nino)事件的影响显著,然而春季AO负位相对随后冬季拉尼娜(La Nina)的影响不明显。本研究分析了30个来自CMIP5的耦合模式对春季AO与随后冬季ENSO不对称性关系的模拟能力。30个CMIP5耦合模式中,只有CNRM-CM5和GISS-E2-H-CC模式能较好地抓住春季AO与冬季ENSO的联系。进一步分析这两个模式中春季AO与冬季ENSO的不对称性关系,发现CNRM-CM5模式能较好地再现春季AO与冬季ENSO的非对称关系,即春季AO正(负)位相会导致赤道中东太平洋出现El Nino(La Nina)型海表温度增暖(冷却)。然而,GISS-E2-H-CC模式的模拟结果显示,春季AO对随后冬季ENSO的影响是对称的。本文随后解释了CNRM-CM5(GISS-E2-H-CC)模式能(不能)模拟出春季AO与冬季ENSO不对称关系的原因。对于CNRMCM5模式,在春季AO正位相年,副热带西北太平洋上空存在明显的异常气旋和正降水异常,正降水异常通过Gill型大气响应对赤道西太平洋异常西风的形成和维持起着重要作用,异常西风通过激发向东传播的暖赤道Kelvin波对随后冬季El Nino事件的发生产生显著的影响;然而,在春季AO负位相年,副热带北太平洋的异常反气旋和负降水异常较弱,导致赤道西太平洋的异常东风不明显,因此,春季AO负异常对随后冬季La Nina的影响不显著。所以,CNRM-CM5模式能够较好地抓住春季AO对随后冬季ENSO事件的非对称性影响。相比之下,对于GISS-E2-H-CC模式,春季AO正(负)位相年副热带西北太平洋上存在显著的正(负)降水异常,通过Gill型大气响应在赤道西太平洋激发出明显的异常西(东)风从而影响随后冬季的El Nino(La Nina)事件。因此,在GISS-E2-H-CC模式中,春季AO对随后冬季ENSO具有对称性影响。另外,模式捕捉春季AO对随后冬季ENSO非对称性影响的能力与模式对春季AO空间结构的模拟能力有一定的联系。 相似文献
10.
基于1957~2017年观测和再分析资料,合成分析了北太平洋年代际振荡(Pacific decadal oscillation,PDO)不同位相下El Ni?o发展年和La Nina年东亚夏季风的环流、降水特征及季节内变化。结果表明,PDO正、负位相作为背景场,分别对El Ni?o发展年、La Nina年东亚夏季风及夏季降水具有加强作用。PDO正位相一方面可增强El Ni?o发展年夏季热带中东太平洋暖海温异常信号,另一方面通过冷海温状态加强中高纬东亚大陆与西北太平洋的环流异常,从而在一定程度上增强了东亚夏季风环流的异常程度;反之,PDO负位相则增强了La Nina年热带海气相互作用以及中高纬环流(如东北亚反气旋)的异常。在季节内变化方面,El Ni?o发展年6月贝湖以东反气旋性环流为东亚地区带来稳定的北风异常,东北亚位势高度减弱;7月开始,环流形势发生调整,日本以东洋面出现气旋性异常,东亚大陆偏北风及位势高度负异常均得到加强;8月,随着东亚夏季风季节进程和El Ni?o发展,西太平洋出现气旋性环流异常,东亚副热带位势高度进一步降低,西北太平洋副热带高压(简称副高)明显东退。La Nina年6月异常较弱,主要环流差异自7月西北太平洋为大范围气旋性异常控制开始,东亚-太平洋遥相关型显著,副高于季节内始终偏弱偏东。上述两种情况下,均造成东亚地区夏季降水总体上偏少,尤其是中国北方降水显著偏少。 相似文献
11.
利用中国气象局上海台风研究所整编的热带气旋(Tropical Cyclone,TC)最佳路径数据集和欧洲中期天气预报中心的ERA再分析资料,分析了El Ni?o-South Oscillation (ENSO)发展年与衰减年西北太平洋(Western North Pacific,WNP)夏季(6—8月)总TC生成频数(Tropical Cyclone Genesis Frequency,TCGF)及其区域性特征,通过潜在生成指数(Genesis Potential Index,GPI)定量诊断各环境要素对TCGF变化的贡献。结果表明,西北太平洋TCGF总数异常在ENSO各位相并不显著,但其东南象限和西部的TCGF异常存在明显差异。在ENSO各位相,GPI异常的空间分布与TCGF异常的空间型相似。同一区域,各环境要素对TCGF异常的贡献不同,反映了ENSO不同位相影响TC生成变化的机理存在差异。WNP东南部(SEWNP)是对ENSO较敏感的区域,El Ni?o发展年,中东太平洋异常增暖激发的Rossby波西传导致SEWNP受异常正涡度环流控制,涡度对TCGF增加的贡献最大;El Ni?o衰减年,西北太平洋出现低层异常反气旋,其东侧异常东北气流将湿度相对较低的水汽输送至SEWNP,相对湿度降低导致TCGF显著减少。La Ni?a发展年,绝对涡度减小和垂直风切变增加对TCGF减少都有影响。WNP西部仅在La Ni?a衰减年出现TCGF显著负异常,低层绝对涡度减小的贡献最大,因为季风槽减弱,抑制了南海附近的TC生成。 相似文献
12.
从短期气候预测关注的外强迫信号角度出发,回顾了国内外在海温异常对东亚夏季风和我国汛期降水影响机理方面的主要研究进展,重点评述了热带太平洋ENSO循环、热带印度洋全区一致型海温模态、热带印度洋海温异常偶极子、南印度洋偶极子和北大西洋海温三极子模态的年际变化及其对东亚夏季风年际变率的影响。从研究成果在短期气候预测业务中应用的角度,重点关注海温异常和东亚夏季风年际变率以及我国汛期降水多雨带位置的关系,总结了海温异常作为外强迫信号对我国汛期降水预测的指示意义以及汛期降水预测的难度。最后指出气候预测业务对东亚夏季风影响的机理研究和动力气候模式发展方面的需求。 相似文献
13.
利用逐月台站观测降水、HadISST1.1海温和ERA5大气再分析资料,研究了前冬印度洋海盆一致模（Indian Ocean Basin,IOB）对华南春季降水（SCSR）与ENSO关系的影响,并分析了IOB通过调控ENSO环流异常进而影响SCSR的可能机制。结果表明:当前冬El Ni?o（La Ni?a）与IOB暖（冷）位相同时发生时,SCSR显著增多（减少）;而当El Ni?o或La Ni?a单独发生而IOB处于中性时,SCSR并无明显多寡倾向。其原因在于,当El Ni?o与IOB暖相位并存时,前冬热带印度洋和赤道中东太平洋均为正海温异常（Sea-Surface Temperature Anomaly,SSTA）,且印度洋SSTA强度可一直维持至春季。在对流层低层,春季赤道中东太平洋的正SSTA激发出异常西北太平洋反气旋（Western North Pacific Anticyclone,WNPAC）。而热带印度洋的正SSTA在副热带印度洋激发出赤道南北反对称环流,赤道以北的东风异常有利于异常WNPAC西伸;赤道以南的西风异常与来自赤道西太平洋的东风异常在东印度洋辐合上升,气流至西北太平洋下沉,形成经向垂直环流,有利于春季WNPAC维持。在对流层高层,印度洋的正SSTA在热带印度洋上空激发出位势高度正异常,随之形成的气压经向梯度加强了东亚高空副热带西风急流,进而在华南上空形成异常辐散环流。WNPAC的西伸和加强可为华南提供充足的水汽,同时高空辐散在华南引发水汽上升运动,共同导致SCSR正异常。而若El Ni?o发生时IOB处于中性状态,El Ni?o相关的SSTA衰减较快,春季WNPAC不显著,SCSR无明显多寡趋势。 相似文献
14.
Predictability of the western North Pacific summer climate associated with different ENSO phases by ENSEMBLES multi-model seasonal forecasts 总被引：1，自引：0，他引：1
Predictability of the western North Pacific (WNP) summer climate associated with different El Niño–Southern Oscillation (ENSO) phases is investigated in this study based on the 1-month lead retrospective forecasts of five state-of-the-art coupled models from ENSEMBLES. During the period from 1960 to 2005, the models well capture the WNP summer climate anomalies during most of years in different ENSO phases except the La Niña decaying summers. In the El Niño developing, El Niño decaying and La Niña developing summers, the prediction skills are high for the WNP summer monsoon index (WNPMI), with the prediction correlation larger than 0.7. The high prediction skills of the lower-tropospheric circulation during these phases are found mainly over the tropical western Pacific Ocean, South China Sea and subtropical WNP. These good predictions correspond well to their close teleconnection with ENSO and the high prediction skills of tropical SSTs. By contrast, for the La Niña decaying summers, the prediction skills are considerably low with the prediction correlation for the WNPMI near to zero and low prediction skills around the Philippines and subtropical WNP. These poor predictions relate to the weak summer anomalies of the WNPMI during the La Niña decaying years and no significant connections between the WNP lower-tropospheric circulation anomalies and the SSTs over the tropical central and eastern Pacific Ocean in observations. However, the models tend to predict an apparent anomalous cyclone over the WNP during the La Niña decaying years, indicating a linearity of the circulation response over WNP in the models prediction in comparison with that during the El Niño decaying years which differs from observations. In addition, the models show considerable capability in describing the WNP summer anomalies during the ENSO neutral summers. These anomalies are related to the positive feedback between the WNP lower-tropospheric circulation and the local SSTs. The models can capture this positive feedback but with some uncertainties from different ensemble members during the ENSO neutral summers. 相似文献
15.
采用1958—2011年NCEP/NCAR再分析资料以及ERSST海温资料,分析热带西太平洋夏季对流10~30 d振荡对南海夏季风的影响。在年际变化尺度上,热带西北太平洋夏季10~30 d振荡强度指数 (TWPI) 与南海夏季风强度有很好的正相关关系。在TWPI增强年份,海温主要呈El Ni?o分布,南海周边区域增强的异常西风产生强的正涡度切变,导致异常气旋性环流,为季风槽的增强提供了热量和水汽,从而增强南海夏季风强度。反之,在TWPI减弱年份,海温主要呈La Ni?a分布,南海夏季风强度减弱。在不同的年代际背景下,垂直切变和水汽-对流的总体变化是影响TWPI总体变化的重要因子,但不能影响南海夏季风强度的总体变化。海陆热力对比的总体变化是导致南海夏季风强度总体变化的主要影响因素。 相似文献
16.
This study investigated the relationship between the asymmetry in the duration of El Ni?o and La Ni?a and the length of their decaying phases. The results suggested that the duration asymmetry comes from the long decaying ENSO cases rather than the short decaying ones. The evolutions of short decaying El Ni?o and La Ni?a are approximately a mirror image with a rapid decline in the following summer for the warm and cold events. However, a robust asymmetry was found in long decaying cases, with a prolonged and re-intensified La Ni?a in the following winter. The asymmetry for long decaying cases starts from the westward extension of the zonal wind anomalies in a mature winter, and is further contributed to by the air-sea interaction over the tropical Pacific in the following seasons. 相似文献
17.
The hydro-climatic variability of the Colombian Andes associated with El Ni?o?CSouthern Oscillation (ENSO) is reviewed using records of rainfall, river discharges, soil moisture, and a vegetation index (NDVI) as a surrogate for evapotranspiration. Anomalies in the components of the surface water balance during both phases of ENSO are quantified in terms of their sign, timing, and magnitude. During El Ni?o (La Ni?a), the region experiences negative (positive) anomalies in rainfall, river discharges (average and extremes), soil moisture, and NDVI. ENSO??s effects are phase-locked to the seasonal cycle, being stronger during December?CFebruary, and weaker during March?CMay. Besides, rainfall and river discharges anomalies show that the ENSO signal exhibits a westerly wave-like propagation, being stronger (weaker) and earlier (later) over the western (eastern) Andes. Soil moisture anomalies are land-cover type dependant, but overall they are enhanced by ENSO, showing very low values during El Ni?o (mainly during dry seasons), but saturation values during La Ni?a. A suite of large-scale and regional mechanisms cooperating at the ocean?Catmosphere?Cland system are reviewed to explaining the identified hydro-climatic anomalies. This review contributes to an understanding of the hydro-climatic framework of a region identified as the most critical hotspot for biodiversity on Earth, and constitutes a wake-up call for scientists and policy-makers alike, to take actions and mobilize resources and minds to prevent the further destruction of the region??s valuable hydrologic and biodiversity resources and ecosystems. It also sheds lights towards the implementation of strategies and adaptation plans to coping with threats from global environmental change. 相似文献
18.
The mechanism for asymmetric atmospheric responses to the central Pacific(CP) El Ni?o and La Ni?a over the western North Pacific(WNP) is studied in this paper. The negative anomalies of rainfall over the key region of WNP are explained by diagnosing the column-integrated equations of moisture and moist static energy(MSE). It is revealed that the nonlinear advection of moist enthalpy is critical to introduce negative rainfall anomalies over the region. The anomalous easterly(westerly) in La Ni?a(CP El Ni?o) causes negative advection of anomalous moist enthalpy, inducing negative heating anomaly and an anticyclone anomaly in the WNP, which weakens(strengthens) the cyclone(anticyclone) in La Ni?a(CP El Ni?o). The MSE budget analysis shows a larger nonlinear term in CP El Ni?o than in eastern Pacific(EP) El Ni?o, inconsistent with the amplitudes of sea surface temperature anomalies. The reason is that the nonlinear term transforms to positive above 700 h Pa in EP El Ni?o, offsetting the negative advection below 700 h Pa and thus making the nonlinear term smaller. The nonlinear term is negative at low levels in CP El Ni?o, resulting in a larger nonlinear term. The stronger precipitation anomalies in the WNP during EP El Ni?o can be attributed to the linear moist enthalpy advection. The mean easterly wind at mid levels causes a larger(smaller) positive moist enthalpy advection in CP(EP) El Ni?o, due to a larger(smaller) moist enthalpy gradient, resulting in a positive(negative) linear moist enthalpy advection, which weakens(strengthens) the negative precipitation anomalies in the key region. 相似文献
19.
The atmospheric and oceanic conditions before the onset of EP El Ni?o and CP El Ni?o in nearly 30 years are compared and analyzed by using 850 hPa wind, 20℃ isotherm depth, sea surface temperature and the Wheeler and Hendon index. The results are as follows: In the western equatorial Pacific, the occurrence of the anomalously strong westerly winds of the EP El Ni?o is earlier than that of the CP El Ni?o. Its intensity is far stronger than that of the CP El Ni?o. Two months before the El Ni?o, the anomaly westerly winds of the EP El Ni?o have extended to the eastern Pacific region, while the westerly wind anomaly of the CP El Ni?o can only extend to the west of the dateline three months before the El Ni?o and later stay there. Unlike the EP El Ni?o, the CP El Ni?o is always associated with easterly wind anomaly in the eastern equatorial Pacific before its onset. The thermocline depth anomaly of the EP El Ni?o can significantly move eastward and deepen. In addition, we also find that the evolution of thermocline is ahead of the development of the sea surface temperature for the EP El Ni?o. The strong MJO activity of the EP El Ni?o in the western and central Pacific is earlier than that of the CP El Ni?o. Measured by the standard deviation of the zonal wind square, the intensity of MJO activity of the EP El Ni?o is significantly greater than that of the CP El Ni?o before the onset of El Ni?o. 相似文献
20.
After its maturity, El Ni?o usually decays rapidly in the following summer and evolves into a La Ni?a pattern. However, this was not the case for the 2018/19 El Ni?o event. Based on multiple reanalysis data sets, the space-time evolution and triggering mechanism for the unusual second-year warming in late 2019, after the 2018/19 El Ni?o event, are investigated in the tropical Pacific. After a short decaying period associated with the 2018/19 El Ni?o condition, positive sea surface temperature anomalies (SSTAs) re-intensified in the eastern equatorial Pacific in late 2019. Compared with the composite pattern of El Ni?o in the following year, two key differences are evident in the evolution of SSTAs in 2019. First, is the persistence of the surface warming over the central equatorial Pacific in May, and second, is the re-intensification of the positive SSTAs over the eastern equatorial Pacific in September. Observational results suggest that the re-intensification of anomalous westerly winds over the western and central Pacific, induced remotely by an extreme Indian Ocean Dipole (IOD) event, acted as a triggering mechanism for the second-year warming in late 2019. That is, the IOD-related cold SSTAs in the eastern Indian Ocean established and sustained anomalous surface westerly winds over the western equatorial Pacific, which induced downwelling Kelvin waves propagating eastward along the equator. At the same time, the subsurface ocean provided plenty of warm water in the western and central equatorial Pacific. Mixed-layer heat budget analyses further confirm that positive zonal advection, induced by the anomalous westerly winds, and thermocline feedback played important roles in leading to the second-year warming in late 2019. This study provides new insights into the processes responsible for the diversity of El Ni?o evolution, which is important for improving the physical understanding and seasonal prediction of El Ni?o events. 相似文献