Impacts of two types of El Niño on atmospheric circulation in the Southern Hemisphere

Based on NCEP/NCAR （National Centers for Environmental Prediction/National Center for Atmo- spheric Research） reanalysis data from 1979 to 2010, the impacts of two types of E1 Nino on atmospheric circulation in the Southern Hemisphere （SH） are analyzed. It is shown thaL when a warming event occurs in the equatorial eastern Pacific （EP E1 Nino）, there is a negative sea level pressure （SLP） anomaly in the east- ern Pacific and a positive one in the western Pacific. Besides, there exists a negative anomaly between 40°S and 60°S and a positive anomaly to the south of 60°S. When a warming event in the central Pacific （CP E1 Nino） occurs, there appears a negative SLP anomaly in the central Pacific and a positive SLP anomaly in the eastern and western Pacific, but the SLP anomalies are not so evident in the SH extratropics. In particular, the Pacific-South America （PSA） pattern induced by the CP E1 Nino is located more northwestward, with a weaker anomaly compared with the EP E1 Nino. This difference is directly related with the different position of heating centers associated with the two types of E1 Nino events. Because the SST anomaly associated with CP E1 Nino is located more westward than that associated with EP El Nino, the related heating center tends to move westward and the response of SH atmospheric circulation to the tropical heating changes accordingly, thus exciting a different position of the PSA pattern. It is also noted that the local meridional cell plays a role in the SH high latitudes during EP E1 Nino. The anomalous ascending motion due to the enhancement of convection over the eastern Pacific leads to an enhancement of the local Hadley cell and the meridional cell in the middle and high latitudes, which in turn induces an anomalous descending motion and the related positive anomaly of geopotential height over the Amundsen-Bellingshausen Sea.     

Extra-tropical atmospheric response to ENSO in the CMIP5 models

The seasonal mean extra-tropical atmospheric response to El Niño/Southern Oscillation (ENSO) is assessed in the historical and pre-industrial control CMIP5 simulations. This analysis considers two types of El Niño events, characterized by positive sea surface temperature (SST) anomalies in either the central equatorial Pacific (CP) or eastern equatorial Pacific (EP), as well as EP and CP La Niña events, characterized by negative SST anomalies in the same two regions. Seasonal mean geopotential height anomalies in key regions typify the magnitude and structure of the disruption of the Walker circulation cell in the tropical Pacific, upper tropospheric ENSO teleconnections and the polar stratospheric response. In the CMIP5 ensembles, the magnitude of the Walker cell disruption is correlated with the strength of the mid-latitude responses in the upper troposphere i.e., the North Pacific and South Pacific lows strengthen during El Niño events. The simulated responses to El Niño and La Niña have opposite sign. The seasonal mean extra-tropical, upper tropospheric responses to EP and CP events are indistinguishable. The ENSO responses in the MERRA reanalysis lie within the model scatter of the historical simulations. Similar responses are simulated in the pre-industrial and historical CMIP5 simulations. Overall, there is a weak correlation between the strength of the tropical response to ENSO and the strength of the polar stratospheric response. ENSO-related polar stratospheric variability is best simulated in the “high-top” subset of models with a well-resolved stratosphere.     

Delayed Impacts of the E1 Nino Episodes in the Central Pacific on the Summertime Climate Anomalies of Eastern China in 2003 and 2007

In the summers of 2003 and 2007, eastern China suffered similar climate disasters with severe flooding in the Huaihe River valley and heat waves in the southern Yangtze River delta and South China. Using SST data and outgoing longwave radiation (OLR) data from NOAA along with reanalysis data from NCEP/NCAR, the 2002/03 and 2006/07 El Ni(n)o episodes in the central Pacific and their delayed impacts on the following early summertime climate anomalies of eastern China were analyzed. The possible physical progresses behaved as follows: Both of the moderate E1 Ni(n)o episodes matured in the central equatorial Pacific during the early winter. The zonal wind anomalies near the sea surface of the west-central equatorial Pacific excited equatorial Kelvin waves propagating eastward and affected the evolution of the E1 Ni(n)o episodes. From spring to early summer, the concurring anomalous easterly winds in the central equatorial Pacific and the end of upwelling Kelvin waves propagating eastward in the western equatorial Pacific, favored the equatorial warm water both of the SST and the subsurface temperature in the western Pacific. These conditions favored the warm state of the western equatorial Pacific in the early summer for both cases of 2003 and 2007. Due to the active convection in the western equatorial Pacific in the early summer and the weak warm SST anomalies in the tropical western Pacific from spring to early summer, the convective activities in the western Pacific warm pool showed the pattern in which the anomalous strong convection only appeared over the southern regions of the tropical western Pacific warm pool, which effects the meridional shift of the western Pacific subtropical high in the summer. The physical progress of the delayed impacts of the E1 Nifio episodes in the central equatorial Pacific and their decaying evolution on the climate anomalies in eastern China were interpreted through the key role of special pattern for the heat convection in the tropical western Pacific warm pool and the response of the western North Pacific anomalous anticyclone.     

Seasonal Evolution of Dominant Modes in South Pacific SST and Relationship with ENSO

A season-reliant empirical orthogonal function(S-EOF) analysis was applied to the seasonal mean SST anomalies(SSTAs) based on the HadISST1 dataset with linear trend removed at every grid point in the South Pacific(60.5-19.5 S,139.5 E-60.5 W) during the period 1979-2009.The spatiotemporal characteristics of the dominant modes and their relationships with ENSO were analyzed.The results show that there are two seasonally evolving dominant modes of SSTAs in the South Pacific with interannual and interdecadal variations;they account for nearly 40% of the total variance.Although the seasonal evolution of spatial patterns of the first S-EOF mode(S-EOF1) did not show remarkable propagation,it decays with season remarkably.The second S-EOF mode(S-EOF2) showed significant seasonal evolution and intensified with season,with distinct characteristics of eastward propagation of the negative SSTAs in southern New Zealand and positive SSTAs southeast of Australia.Both of these two modes have significant relationships with ENSO.These two modes correspond to the post-ENSO and ENSO turnabout years,respectively.The SEOF1 mode associated with the decay of the eastern Pacific(EP) and the central Pacific(CP) types of ENSO exhibited a more significant relationship with the EP/CP type of El Nin o than that with the EP/CP type of La Nin a.The S-EOF2 mode contacted with the EP type of El Nin o changing into the EP/CP type of La Nin a showed a more significant connection with the EP/CP type of La Nin a.     

两类ENSO背景下中国东部夏季降水的环流特征及关键系统

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。     

Nonlinearity Modulating Intensities and Spatial Structures of Central Pacific and Eastern Pacific El Nio Events

This paper compares data from linearized and nonlinear Zebiak–Cane model, as constrained by observed sea surface temperature anomaly(SSTA), in simulating central Pacific(CP) and eastern Pacific(EP) El Nio. The difference between the temperature advections(determined by subtracting those of the linearized model from those of the nonlinear model),referred to here as the nonlinearly induced temperature advection change(NTA), is analyzed. The results demonstrate that the NTA records warming in the central equatorial Pacific during CP El Nio and makes fewer contributions to the structural distinctions of the CP El Nio, whereas it records warming in the eastern equatorial Pacific during EP El Nio, and thus significantly promotes EP El Nio during El Nio–type selection. The NTA for CP and EP El Nio varies in its amplitude,and is smaller in CP El Nio than it is in EP El Nio. These results demonstrate that CP El Nio are weakly modulated by small intensities of NTA, and may be controlled by weak nonlinearity; whereas, EP El Nio are significantly enhanced by large amplitudes of NTA, and are therefore likely to be modulated by relatively strong nonlinearity. These data could explain why CP El Nio are weaker than EP El Nio. Because the NTA for CP and EP El Nio differs in spatial structures and intensities, as well as their roles within different El Nio modes, the diversity of El Nio may be closely related to changes in the nonlinear characteristics of the tropical Pacific.     

AN OPERATIONAL AUTO-MONITORING FOR THE EL NINO EPISODES USING GMS TBB

By making full use of GMS TBB data, diagnosis and analysis of the formation and development of El Nino event in 2002 and 2003 were made. It suggests that the first clue of the El Nino event appeared in December 2001. The event was formed at the end of 2002 after five phases of development, and came into the phase of flourishing in the winter of 2002. From the analysis the dynamics, it is noted that that the position of the ascending branch of Walker cell was moving from the equatorial west Pacific to the equatorial central Pacific in the phase of formation and development of the El Nino event. The process of diagnosis shows that it can provide an important clue for forecasting the genesis and development of the El Nino episodes.     

The Impacts of Two Types of El Ni（n）o on Global Ozone Variations in the Last Three Decades

The effects of E1Nifio Modoki events on global ozone concentrations are investigated from 1980 to 2010 E1 Nifio Modoki events cause a stronger Brewer-Dobson （BD） circulation which can transports more ozone-poor air from the troposphere to stratosphere, leading to a decrease of ozone inthe lower-middle stratosphere from 90~S to 90~N. These changes in ozone concentrations reduce stratospheric column ozone. The reduction in stratospheric column ozone during E1 Nifio Modoki events is more pronounced over the tropical eastern Pacific than over other tropical areas because transport of ozone-poor air from middle-high latitudes in both hemispheres to low latitudes is the strongest between 60°W and 120°W. Because of the decrease in stratospheric column ozone during E1 Nifio Modoki events more UV radiation reaches the tropical troposphere leading to significant increases in tropospheric column ozone An empirical orthogonal function （EOF） analysis of the time series from 1980 to 2010 of stratospheric and tropospheric ozone monthly anomalies reveals that： E1 Nifio Modoki events are associated with the primary EOF modes of both time series. We also found that E1 Nifio Modoki events can affect global ozone more significantly than canonical E1 Nifio events. These results imply that E1 Nifio Modoki is a key contributor to variations in global ozone from 1980 to 2010.     

The Relationship between the El Ni ?no/La Ni ?na Cycle and the Transition Chains of Four Atmospheric Oscillations. Part II: The Relationship and a New Approach to the Prediction of El Ni ?no

ABSTRACT The authors explored the connection and transition chains of the Northern Oscillation （NO） and the North Pacific Oscilla tion （NPO）, the Southern Oscillation （SO）, and the Antarctic Oscillation （AAO） on the interannual timescale in a companion paper. In this study, the connection between the transition chains of the four oscillations （the NO and NPO, the SO and AAO） and the El Nifio/La Nifia cycle were examined. It was found that during the transitions of the four oscillations, alternate anticyclonic/cyclonic correlation centers propagated from the Western Pacific to the Eastern Pacific along both sides of the equator. Between the anticyclonic/cyclonic correlation centers, the zonal wind anomalies also moved eastwardly, favoring the advection of sea surface temperature anomalies from the tropical Western Pacific to the Eastern Pacific. When the anti cyclonic anomalies arrived in the Eastern Pacific, the positive phase of NO/SO and La Nifia were established and vice versa. Thus, in 4-6 years, with an entire transition chain of the four oscillations, an E1 Nifio/La Nifia cycle completed. The eastward propagation of the covarying anomalies of the sea level pressure, zonal wind, and sea surface temperature was critical to the transition chains of the four oscillations and the cycle of E1 Nifio/La Nifia. Based on their close link, a new empirical prediction method of the timing of E1 Nifio by the transition chains of the four oscillations was proposed. The assessment provided confidence in the ability of the new method to supply information regarding the long-term variations of the ocean and atmosphere in the tropical Pacific.     

A new paradigm for the predominance of standing Central Pacific Warming after the late 1990s

Canonical El Niño has a warming center in the eastern Pacific (EP), but in recent decades, El Niño warming center tends to occur more frequently in the central Pacific (CP). The definitions and names of this new type of El Niño, however, have been notoriously diverse, which makes it difficult to understand why the warming center shifts. Here, we show that the new type of El Niño events is characterized by: 1) the maximum warming standing and persisting in the CP and 2) the warming extending to the EP only briefly during its peak phase. For this reason, we refer to it as standing CP warming (CPW). Global warming has been blamed for the westward shift of maximum warming as well as more frequent occurrence of CPW. However, we find that since the late 1990s the standing CPW becomes a dominant mode in the Pacific; meanwhile, the epochal mean trade winds have strengthened and the equatorial thermocline slope has increased, contrary to the global warming-induced weakening trades and flattening thermocline. We propose that the recent predominance of standing CPW arises from a dramatic decadal change characterized by a grand La Niña-like background pattern and strong divergence in the CP atmospheric boundary layer. After the late 1990s, the anomalous mean CP wind divergence tends to weaken the anomalous convection and shift it westward from the underlying SST warming due to the suppressed low-level convergence feedback. This leads to a westward shift of anomalous westerly response and thus a zonally in-phase SST tendency, preventing eastward propagation of the SST anomaly. We anticipate more CPW events will occur in the coming decade provided the grand La Niña-like background state persists.     

与不同El Nino相伴的IOD事件的季节演变特征对比

基于1951—2012年逐月海洋和大气多种要素的再分析资料,分析了与两类El Nino相伴的IOD(Indian Ocean Dipole,印度洋偶极子)事件盛期的海洋和大气异常特征,并进一步对比了与不同类型El Nino相伴的IOD事件的季节演变及对应的海气耦合过程。结果表明:两类IOD事件盛期时,暖海温强度和位置有显著差异。发生在东部型El Nino期间的IOD事件(简称EP-IOD)盛期,正(负)SSTA中心出现在热带西北(赤道东南)印度洋,强度相当,对应的热带印度洋—海洋大陆异常Walker环流强度较强、范围较大;与中部型CP El Nino相伴的IOD事件(简称CP-IOD)的正SSTA相对较弱,且偏于南印度洋,异常Walker环流较弱、较窄。在季节演变中,两类IOD事件期间的局地海气过程差异显著,伴随着西印度洋西南季风减弱和东印度洋异常东风加强,EP-IOD事件的发展以西正东负的偶极型异常海温的出现及加强为主要特征;而CP-IOD事件的发生发展则与西北印度洋异常冷海温的生消及南印度洋暖水的堆积相伴,表现为"-+-"三极型SSTA的出现并转为西正东负偶极型的过程,夏季时出现在东印度洋的异常东风以及赤道中印度洋低层负涡度异常水平环流对其发展具有重要作用。     

热带太平洋与印度洋相互作用的年代际变化及其数值模拟

利用全球海表温度资料和NCEP／NCAR再分析资料,发现热带印度洋偶极子事件与热带太平洋ENSO事件存在相互作用,但其相互作用关系在1961年前后发生了明显的跃变。通过CCM3（community climate model version3）模式,研究了不同年代热带太平洋和热带印度洋SST（seasur—face temperature）变化对其上空大气环流影响的变化,结果表明：1961年后,热带印度洋发生正偶极子事件时,两大洋的垂直环流异常的耦合很强,热带太平洋上空大气环流对印度洋偶极子事件的响应,给太平洋暖事件的异常发展提供了有利条件;同样,热带太平洋暖事件通过对热带印度洋上空大气环流的影响,给印度洋偶极子的异常发展提供了有利条件。     

Impacts of Two Types of El Ni o on the MJO during Boreal Winter

The features of the MJO during two types of El Ni no events are investigated in this paper using the daily NCEP-2reanalysis data, OLR data from NOAA, and Real-time Multivariate MJO index for the period 1979–2012. The results indicate that the MJO exhibits distinct features during eastern Pacific(EP) El Ni no events, as compared to central Pacific(CP) El Ni no events. First, the intensity of the MJO is weakened during EP El Ni no winters from the tropical eastern Indian Ocean to the western Pacific, but enhanced during CP El Ni no winters. Second, the range of the MJO eastward propagation is different during the two types of El Ni no events. During EP El Ni no winters, the MJO propagates eastwards to 120?W, but only to 180?during CP El Ni no winters. Finally, the frequency in eight phases of the MJO may be affected by the two types of El Ni no. Phases 2 and 3 display a stronger MJO frequency during EP El Ni no winters, but phases 4 and 5 during CP El Ni no winters.     

Subsurface ocean temperature indices for Central-Pacific and Eastern-Pacific types of El Ni?o and La Ni?a events

Subsurface ocean temperature indices are developed to identify two distinct types of tropical Pacific warming (El Ni?o) and cooling (La Ni?a) events: the Eastern-Pacific (EP) type and the Central-Pacific (CP) type. Ocean temperature anomalies in the upper 100?m are averaged over the eastern (80°W?C90°W, 5°S?C5°N) and central (160°E?C150°W, 5°S?C5°N) equatorial Pacific to construct the EP and CP subsurface indices, respectively. The analysis is performed for the period of 1958?C2001 using an ocean data assimilation product. It is found that the EP/CP subsurface indices are less correlated and show stronger skewness than the sea surface temperature (SST)-based indices. In addition, while both quasi-biennial (??2?years) and quasi-quadrennial (??4?years) periodicities appear in the SST-based indices for these two types, the subsurface indices are dominated only by the quasi-biennial periodicity for the CP type and by the quasi-quadrennial (??4?years) periodicity for the EP type. Low correlation, high skewness, and single leading periodicity are desirable properties for defining indices to separate the EP and CP types. Using the subsurface indices, major El Ni?o and La Ni?a events identified by the Ni?o-3.4 SST index are classified as the EP or CP types for the analysis period. It is found that most strong El Ni?o events are of the EP type while most strong La Ni?a events are of the CP type. It is also found that strong CP-type La Ni?a events tend to occur after strong EP-type El Ni?o events. The reversed subsequence (i.e., strong EP El Ni?o events follow strong CP La Ni?a events) does not appear to be typical. This study shows that subsurface ocean indices are an effective way to identify the EP and CP types of Pacific El Ni?o and La Ni?a events.     

Vertical structure variability and equatorial waves during central Pacific and eastern Pacific El Ni?os in a coupled general circulation model

Recent studies report that two types of El Ni?o events have been observed. One is the cold tongue El Ni?o or Eastern Pacific El Ni?o (EP El Ni?o), which is characterized by relatively large sea surface temperature (SST) anomalies in the eastern Pacific, and the other is the warm pool El Ni?o (a.k.a. ‘Central Pacific El Ni?o’ (CP El Ni?o) or ‘El Ni?o Modoki’), in which SST anomalies are confined to the central Pacific. Here the vertical structure variability of the periods during EP and CP is investigated based on the GFDL_CM2.1 model in order to explain the difference in equatorial wave dynamics and associated negative feedback mechanisms. It is shown that the mean stratification in the vicinity of the thermocline of the central Pacific is reduced during CP El Ni?o, which favours the contribution of the gravest baroclinic mode relatively to the higher-order slower baroclinic mode. Energetic Kelvin and first-meridional Rossby wave are evidenced during the CP El Ni?o with distinctive amplitude and propagating characteristics according to their vertical structure (mostly first and second baroclinic modes). In particular, the first baroclinic mode during CP El Ni?o is associated to the ocean basin mode and participates to the recharge process during the whole El Ni?o cycle, whereas the second baroclinic mode is mostly driving the discharge process through the delayed oscillator mechanism. This may explain that the phase transition from warm to neutral/cold conditions during the CP El Ni?o is delayed and/or disrupted compared to the EP El Ni?o. Our results have implications for the interpretation of the variability during periods of high CP El Ni?o occurrence like the last decade.     

两类El Ni?o事件对华南前汛期降水异常的影响

利用观测资料及模式结果探讨了EP/CP El Ni?o事件对华南前汛期（4—6月）降水异常的影响。结果发现,EP和CP型相关的华南前汛期降水异常分布之间存在明显月际差异,表现为4、5月EP（CP）型相关的降水异常以偏多（少）为主;6月则相反,EP（CP）型的降水呈负（正）异常分布。分析表明,EP型相关的4、5月偏强的副热带高压与850 hPa上西北太平洋反气旋异常相配合,有利于水汽从海洋向陆地输送,且两广地区水汽辐合,降水异常偏多;而6月相关的500 hPa异常场上对应偏强的东亚大槽,不利于水汽输送,且广东地区处于水汽辐散区,对应降水偏少。CP型相关的4、5月对应500 hPa上东亚大槽偏强,不利于水汽往陆地输送,且华南为水汽辐散,降水偏少;6月的500 hPa上呈现“+-+”的东亚-太平洋遥相关波列（EAP）型,华南地区为明显的水汽辐合,降水偏多。GFDL模式较好地再现了EP /CP型的4、5月降水异常分布及大气环流形势,但是对6月的模拟存在一定偏差。      

东部型和中部型厄尔尼诺事件对山东夏季降水的不同影响

利用1951—2017年NOAA月平均海面温度、NCEP/NCAR的再分析资料以及中国160站月降水观测资料,通过分类合成分析方法研究了东部型（eastern Pacific,EP）和中部型（central Pacific,CP）厄尔尼诺（El Niño）事件当年及次年对山东夏季降水年际变化的影响。结果表明,两类El Niño发生年,山东夏季降水均较常年显著偏少,但EP El Niño对山东夏季降水的影响强度和范围略弱于CP El Niño：EP El Niño发生年夏季,仅鲁西北部分地区以及胶州湾附近降水较常年显著偏少,而CP El Niño当年夏季山东全区降水较常年显著偏少。EP El Niño和CP El Niño次年对山东夏季降水异常的影响呈反位相,且影响大值区空间位置也完全相反：EP El Niño次年夏季山东东部尤其是半岛地区降水较常年异常偏少（青岛地区最为突出）,而CP El Niño次年夏季山东中部和北部尤其是西北部地区降水较常年异常偏多。EP El Niño当年和次年夏季、CP El Niño当年夏季500 hPa高度场异常分布形势不利于西北太平洋副热带高压的北上,850 hPa风场为偏北风和偏东风异常,山东水汽输送条件差,水汽无明显辐合,造成大部分地区降水偏少。CP El Niño次年夏季西北太平洋副热带高压偏强,位置偏西偏北,850 hPa显著西南风场异常,山东中西部水汽辐合明显,这些是降水偏多的重要原因。     

The role of mean state on changes in El Niño’s flavor

Recently, many studies have argued for the existence of two types of El Niño phenomena based on different spatial distributions: the conventional El Niño [or Eastern Pacific (EP) El Niño], and the Central Pacific (CP) El Niño. Here, we investigate the decadal modulation of CP El Niño occurrences using a long-term coupled general circulation model simulation, focusing, in particular, on the role of climate state in the regime change between more and fewer CP El Niño events. The higher occurrence regime of the CP El Niño coincides with the lower occurrence regime of EP El Niño, and vice versa. The climate states associated with these two opposite regimes resemble the leading principal component analysis (PCA) modes of tropical Pacific decadal variability, indicating that decadal change in climate state may lead to regime change in terms of two different types of El Niño. In particular, the higher occurrence regime of CP El Niño is associated with a strong zonal gradient of mean surface temperature in the equatorial Pacific, along with a strong equatorial Trade wind over the area east of the dateline. In addition, the oceanic variables—the mixed layer depth and the thermocline depth—show values indicating increased depth over the western-to-central Pacific. The aforementioned climate states obviously intensify zonal advective feedback, which promotes increased generation of the CP El Niño. Frequent CP El Niño occurrences are not fully described by oceanic subsurface dynamics, and dynamical or thermodynamical processes in the ocean mixed layer and air–sea interaction are important contributors to the generation of the CP El Niño. Furthermore, the atmospheric response with respect to the SSTA tends to move toward the west, which leads to a weak air–sea coupling over the eastern Pacific. These features could be regarded as evidence that the climate state can provide a selection mechanism of the El Niño type.     

Mean Flow–Storm Track Relationship and Rossby Wave Breaking in Two Types of El-Nino简

The features of large-scale circulation, storm tracks and the dynamical relationship between them were examined by investigating Rossby wave breaking （RWB） processes associated with Eastern Pacific （EP） and Central Pacific （CP） E1-Nifio. During EP E1-Nino, the geopotential height anomaly at 500 hPa （Z500） exhibits a Pacific-North America （PNA） pattern. During CP EI-Nifio, the Z500 anomaly shows a north positive-south negative pattern over the North Pacific. The anomalous distributions of baroclinicity and storm track are consistent with those of upper-level zonal wind for both EP and CP EI-Nino, suggesting impacts of mean flow on storm track variability. Anticyclonic wave breaking （AWB） oczurs less frequently in EP EI-Nino years, while cyclonic wave breaking （CWB） occurs more frequently in CP EI-Nino years over the North Pacific sector. Outside the North Pacific, more CWB events occur over North America during EP Ei-NiNo. When AWB events occur less frequently over the North Pacific during EP EI-Nino, Z500 decreases locally and the zonal wind is strengthened （weakened） to the south （north）. This is because AWB events reflect a monopoie high anomaly at the centroid of breaking events. When CWB events occur more frequently over the North Pacific under CP EI-Nino conditions, and over North America under EP EI-Nino condition, Z500 increases （decreases） to the northeast （southwest）, since CWB events are related to a northeast-southwest dipole Z500 anomaly. The anomalous RWB events act to invigorate and reinforce the circulation anomalies over the North Pacific-North America region linked with the two types of EI-Nino.     

两种厄尔尼诺类型期高原地区大气环流的对比分析

本文利用NCEP/NCAR再分析资料,分析了增温区域不同的两类El－Nino事件各阶段的特征,及其次年夏季高原地区的风场、温度场以及高原上空的南亚高压的高度场分布特征。结果表明:对风场环流的不同影响主要表现在:从垂直剖面图来看EP型整体都是东风增强,而CP型在对流层的中下层为西风增强,上层为东风增强;200hPa风场EP型高原上空为异常东风,而CP型为一异常切变线,北边异常东北风,南边异常东南风;500hPa风场EP型表现为异常东北风,CP型为异常东南风。对温度场的不同影响主要表现在:EP型在高原上空对流层中层和高层各有一个负异常中心,而CP型只在中层有一个负异常中心;对南亚高压的不同影响主要表现在:EP型南亚高压中心位置偏东南,而CP型南亚高压中心位置则偏北。