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1.
It has long been acknowledged that there are two types of El Nio events, i.e., the eastern Pacific El Nio (EE) and the central Pacific El Nio (CE), according to the initial position of the anomalous warm water and its propagation direction. In this paper, the oceanic and atmospheric evolutions and the possible mechanisms of the two types of El Nio events were examined. It is found that all the El Nio events, CE or EE, could be attributed to the joint impacts of the eastward advection of warm water from... 相似文献
2.
In recent decades, the typical El Nio events with the warmest SSTs in the tropical eastern Pacific have become less common, and a different of El Nio with the warmest SSTs in the central Pacific, which is flanked on the east and west by cooler SSTs, has become more fre-quent. The more recent type of El Nio was referred to as central Pacific El Nio, warm pool El Nio, or dateline El Nio, or the El Nio Modoki. Central Pacific El Nio links to a different tropical-to-extratropical teleconnection and exerts different impacts on climate, and several classification approaches have been proposed. In this study, a new classification approach is proposed, which is based on the linear combination (sum or difference) of the two leading Empirical Orthogonal Functions (EOFs) of tropical Pacific Ocean sea surface temperature anomaly (SSTA), and the typical El Ni o index (TENI) and the central El Nio index (CENI) are able to be derived by projecting the observed SSTA onto these combinations. This classification not only reflects the characteristics of non-orthogonality between the two types of events but also yields one period peaking at approximate two to seven years. In particular, this classification can distin-guish the different impacts of the two types of events on rainfall in the following summer in East China. The typical El Nio events tend to induce intensified rainfall in the Yangtze River valley, whereas the central Pacific El Nio tends to induce intensified rainfall in the Huaihe River valley. Thus, the present approach may be appropriate for studying the impact of different types of El Nio on the East Asian climate. 相似文献
3.
《大气和海洋科学快报》2012,(5)
正In recent decades, the typical El Nio events with the warmest SSTs in the tropical eastern Pacific have become less common, and a different of El Nio with the warmest SSTs in the central Pacific, which is flanked on the east and west by cooler SSTs, has become more fre-quent. The more recent type of El Nio was referred to as central Pacific El Nio, warm pool El Nio, or dateline El Nio, or the El Nio Modoki. Central Pacific El Nio links to a different tropical-to-extratropical teleconnection and exerts different impacts on climate, and several classification approaches have been proposed. In this study, a new classification approach is proposed, which is based on the linear combination (sum or difference) of the two leading Empirical Orthogonal Functions (EOFs) of tropical Pacific Ocean sea surface temperature anomaly (SSTA), and the typical El Ni o index (TENI) and the central El Nio index (CENI) are able to be derived by projecting the observed SSTA onto these combinations. This classification not only reflects the characteristics of non-orthogonality between the two types of events but also yields one period peaking at approximate two to seven years. In particular, this classification can distin-guish the different impacts of the two types of events on rainfall in the following summer in East China. The typical El Nio events tend to induce intensified rainfall in the Yangtze River valley, whereas the central Pacific El Nio tends to induce intensified rainfall in the Huaihe River valley. Thus, the present approach may be appropriate for studying the impact of different types of El Nio on the East Asian climate. 相似文献
4.
A comparison of sensitivity in extratropical circulation in the Northern Hemisphere(NH)and Southern Hemisphere(SH)is conducted through observational analyses and diagnostic linear model experiments for two types of El Nio events,the traditional El Nio with the strongest warmth in the eastern tropical Pacific(EP El Nio)and the El Nio Modoki with the strongest warmth in the central tropical Pacific(CP El Nio).It is shown that CP El Nio favors the occurrence of a negative-phase Northern Annular Mode(NAM),while EP El Nio favors that of the Pacific-North American(PNA)pattern.In SH,both EP and CP El Nio induce a negative phase Southern Annular Mode(SAM).However,the former has a greater amplitude,which is consistent with the stronger sea surface temperature(SST)warmth.The difference in the two types of El Nio events in NH may originate from the dependence of heating-induced extratropical response on the location of initial heating,which may be associated with activity of the stationary wave.In SH,the lack of sensitivity to the location of heating can be associated with weaker activity of the stationary wave therein. 相似文献
5.
Distinguished Effects of Interannual Salinity Variability on the Development of the Central-Pacific El Ni o Events 
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下载免费PDF全文 《大气和海洋科学快报》2012,(2)
El Nio events in the central equatorial Pacific (CP) are gaining increased attention,due to their increasing intensity within the global warming context.Various physical processes have been identified in the climate system that can be responsible for the modulation of El Nio,especially the effects of interannual salinity variability.In this work,a comprehensive data analysis is performed to illustrate the effects of interannual salinity variability using surface and subsurface salinity fields from the Met Office ENSEMBLES (EN3) quality controlled ocean dataset.It is demonstrated that during the developing phase of an El Nio event,a negative sea surface salinity (SSS) anomaly in the western-central basin acts to freshen the mixed layer (ML),decrease oceanic density in the upper ocean,and stabilize the upper layers.These related oceanic processes tend to reduce the vertical mixing and entrainment of subsurface water at the base of the ML,which further enhances the warm sea surface temperature (SST) anomalies associated with the El Nio event.However,the effects of interannually variable salinity are much more significant during the CP-El Nio than during the eastern Pacific (EP) El Nio,indicating that the salinity effect might be an important contributor to the development of CP-El Nio events. 相似文献
6.
Distinguished Effects of Interannual Salinity Variability on the Development of the Central-Pacific El Nino Events 下载免费PDF全文
下载免费PDF全文 El Nio events in the central equatorial Pacific (CP) are gaining increased attention,due to their increasing intensity within the global warming context.Various physical processes have been identified in the climate system that can be responsible for the modulation of El Nio,especially the effects of interannual salinity variability.In this work,a comprehensive data analysis is performed to illustrate the effects of interannual salinity variability using surface and subsurface salinity fields from the Met Office ENSEMBLES (EN3) quality controlled ocean dataset.It is demonstrated that during the developing phase of an El Nio event,a negative sea surface salinity (SSS) anomaly in the western-central basin acts to freshen the mixed layer (ML),decrease oceanic density in the upper ocean,and stabilize the upper layers.These related oceanic processes tend to reduce the vertical mixing and entrainment of subsurface water at the base of the ML,which further enhances the warm sea surface temperature (SST) anomalies associated with the El Nio event.However,the effects of interannually variable salinity are much more significant during the CP-El Nio than during the eastern Pacific (EP) El Nio,indicating that the salinity effect might be an important contributor to the development of CP-El Nio events. 相似文献
7.
In recent years, El Nio Modoki (a type of pseudo-El Nio) has been distinguished as a unique large-scale ocean warming phenomenon happening in the central tropical Pacific that is quite different from the traditional El Nio. In this study, EOF analysis was used to successfully separate El Nio and El Nio Modoki. The abilities of the NINO3 index, NINO3.4 index, NINO1+2 index and NINO4 index in characterizing El Nio were explored in detail. The resulting suggestion was that, comparatively, NINO3 is the op... 相似文献
8.
The 2015/16 El Ni?o displayed a distinct feature in the SST anomalies over the far eastern Pacific(FEP)compared to the 1997/98 extreme case.In contrast to the strong warm SST anomalies in the FEP in the 1997/98 event,the FEP warm SST anomalies in the 2015/16 El Ni?o were modest and accompanied by strong southeasterly wind anomalies in the southeastern Pacific.Exploring possible underlying causes of this distinct difference in the FEP may improve understanding of the diversity of extreme El Ni?os.Here,we employ observational analyses and numerical model experiments to tackle this issue.Mixed-layer heat budget analysis suggests that compared to the 1997/98 event,the modest FEP SST warming in the 2015/16 event was closely related to strong vertical upwelling,strong westward current,and enhanced surface evaporation,which were caused by the strong southeasterly wind anomalies in the southeastern Pacific.The strong southeasterly wind anomalies were initially triggered by the combined effects of warm SST anomalies in the equatorial central and eastern Pacific(CEP)and cold SST anomalies in the southeastern subtropical Pacific in the antecedent winter,and then sustained by the warm SST anomalies over the northeastern subtropical Pacific and CEP.In contrast,southeasterly wind anomalies in the 1997/98 El Ni?o were partly restrained by strong anomalously negative sea level pressure and northwesterlies in the northeast flank of the related anomalous cyclone in the subtropical South Pacific.In addition,the strong southeasterly wind and modest SST anomalies in the 2015/16 El Ni?o may also have been partly related to decadal climate variability. 相似文献
9.
《大气和海洋科学快报》2012,(5)
The authors demonstrate that the El Ni o events in the pre-and post-1976 periods show two ampli-tude-duration relations. One is that the stronger El Ni o events have longer durations, which is robust for the moderate El Ni o events; the other is that the stronger El Ni o events have shorter durations but for strong El Nio events. By estimating the sign and amplitude of the nonlinear dynamical heating (NDH) anomalies, the authors illustrate that the NDH anomalies are negligible for moderate El Nio events but large for strong El Nio events. In particular, the large NDH anomalies for strong El Nio events are positive during the growth and mature phases, which favor warmer El Nio events. During the decay phase, however, the negative NDH anomalies start to arise and become increasingly significant with the evolution of the El Nio events, in which the negative NDH anomalies dampen the sea surface temperature anomalies (SSTA) and cause the El Nio events to reach the SST normal state earlier. This pattern suggests that the nonlinearity tends to increase the intensities of strong El Nio events and shorten their duration, which, together with the previous results showing a positive correlation between the strength of El Nio events and the significance of the effect of nonlinear advection on the events (especially the suppression of nonlinearity on the SSTA during the decay phase), shows that the strong El Nio events tend to have the amplitude-duration relation of the stronger El Nio events with shorter durations. This result also lends support to the assertion that moderate El Nio events possess the amplitude-duration relation of stronger El Nio events with longer durations. 相似文献
10.
The authors demonstrate that the El Ni o events in the pre-and post-1976 periods show two ampli-tude-duration relations. One is that the stronger El Ni o events have longer durations, which is robust for the moderate El Ni o events; the other is that the stronger El Ni o events have shorter durations but for strong El Nio events. By estimating the sign and amplitude of the nonlinear dynamical heating (NDH) anomalies, the authors illustrate that the NDH anomalies are negligible for moderate El Nio events but large for strong El Nio events. In particular, the large NDH anomalies for strong El Nio events are positive during the growth and mature phases, which favor warmer El Nio events. During the decay phase, however, the negative NDH anomalies start to arise and become increasingly significant with the evolution of the El Nio events, in which the negative NDH anomalies dampen the sea surface temperature anomalies (SSTA) and cause the El Nio events to reach the SST normal state earlier. This pattern suggests that the nonlinearity tends to increase the intensities of strong El Nio events and shorten their duration, which, together with the previous results showing a positive correlation between the strength of El Nio events and the significance of the effect of nonlinear advection on the events (especially the suppression of nonlinearity on the SSTA during the decay phase), shows that the strong El Nio events tend to have the amplitude-duration relation of the stronger El Nio events with shorter durations. This result also lends support to the assertion that moderate El Nio events possess the amplitude-duration relation of stronger El Nio events with longer durations. 相似文献
11.
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
12.
ECHAM5-Simulated Impacts of Two Types of El Nio on the Winter Precipitation Anomalies in South China 下载免费PDF全文
下载免费PDF全文 The authors used an atmospheric general circulation model(AGCM) of European Centre Hamburg Model(ECHAM5.4) and investigated the possible impacts of eastern Pacific(EP) and central Pacific(CP) El Nio on the winter precipitation anomalies in South China.A composite analysis suggested much more rainfall during the mature phase of EP El Nio than in the case of CP El Nio,and their corresponding observed wet centers to be located in the southeast coast and the region to the south of the Yangtze River,respectively.Results obtained on the basis of model-sensitive run imply that the modelsimulated rainfall anomalies agree well with the observation,and the magnitude of simulated rainfall anomalies were found to be reduced when the amplitude of sea surface temperature anomaly(SSTA) forcing of EP and CP El Nio was cut down.These results imply that the rainfall anomaly in South China is very sensitive not only to the type of El Nio but also to its intensity. 相似文献
13.
After compositing three representative ENSO indices,El Nio events have been divided into an eastern pattern(EP) and a central pattern(CP).By using EOF,correlation and composite analysis,the relationship and possible mechanisms between Indian Ocean Dipole(IOD) and two types of El Nio were investigated.IOD events,originating from Indo-Pacific scale air-sea interaction,are composed of two modes,which are associated with EP and CP El Ni o respectively.The IOD mode related to EP El Nio events(named as IOD1) is strongest at the depth of 50 to 150 m along the equatorial Indian Ocean.Besides,it shows a quasi-symmetric distribution,stronger in the south of the Equator.The IOD mode associated with CP El Nio(named as IOD2) has strongest signal in tropical southern Indian Ocean surface.In terms of mechanisms,before EP El Nio peaks,anomalous Walker circulation produces strong anomalous easterlies in equatorial Indian Ocean,resulting in upwelling in the east,decreasing sea temperature there;a couple of anomalous anticyclones(stronger in the south) form off the Equator where warm water accumulates,and thus the IOD1 occurs.When CP El Nio develops,anomalous Walker circulation is weaker and shifts its center to the west,therefore anomalous easterlies in equatorial Indian Ocean is less strong.Besides,the anticyclone south of Sumatra strengthens,and the southerlies east of it bring cold water from higher latitudes and northerlies west of it bring warm water from lower latitudes to the 15° to 25°S zone.Meanwhile,there exists strong divergence in the east and convergence in the west part of tropical southern Indian Ocean,making sea temperature fall and rise separately.Therefore,IOD2 lies farther south. 相似文献
14.
A central Pacific(CP) El Ni?o event occurred in 2018/19. Previous studies have shown that different mechanisms are responsible for different subtypes of CP El Ni?o events(CP-I El Ni?o and CP-II El Ni?o). By comparing the evolutions of surface winds, ocean temperatures, and heat budgets of the CP-I El Ni?o, CP-II El Ni?o, and 2018/19 El Ni?o, it is illustrated that the subtropical westerly anomalies in the North Pacific, which led to anomalous convergence of Ekman flow and surface warming in the ... 相似文献
15.
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 Nio. 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 Nio and makes fewer contributions to the structural distinctions of the CP El Nio, whereas it records warming in the eastern equatorial Pacific during EP El Nio, and thus significantly promotes EP El Nio during El Nio–type selection. The NTA for CP and EP El Nio varies in its amplitude,and is smaller in CP El Nio than it is in EP El Nio. These results demonstrate that CP El Nio are weakly modulated by small intensities of NTA, and may be controlled by weak nonlinearity; whereas, EP El Nio 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 Nio are weaker than EP El Nio. Because the NTA for CP and EP El Nio differs in spatial structures and intensities, as well as their roles within different El Nio modes, the diversity of El Nio may be closely related to changes in the nonlinear characteristics of the tropical Pacific. 相似文献
16.
The mid-Pliocene, the most recent warm geological period, is thought to be indicative of the fate of the Earth's climate under global warming. Earlier evidence has suggested that permanent El Nio-like conditions existed in the mid-Pliocene, though the concept of a permanent El Nio remains controversial. Here, the authors analyzed Nio 3.4 SST in pre-industrial and mid-Pliocene simulations with the low-resolution version of the Norwegian Earth System Model (NorESM-L). The simulated mid-Pliocene Nio3.4 SST, with a smaller standard deviation, indicated that a weaker ENSO existed in the mid-Pliocene relative to the pre-industrial experiment. Compared with earlier modeling studies, our simulations show that the problem of ENSO's standard deviations in the mid-Pliocene remains unresolved, although the mean and the period of ENSO in the mid-Pliocene have been resolved by earlier geological and modeling studies. 相似文献
17.
The relationships between the tropical Indian Ocean basin(IOB)/dipole(IOD) mode of SST anomalies(SSTAs) and ENSO phase transition during the following year are examined and compared in observations for the period 1958–2008.Both partial correlation analysis and composite analysis show that both the positive(negative) phase of the IOB and IOD(independent of each other) in the tropical Indian Ocean are possible contributors to the El Nio(La Nia) decay and phase transition to La Nia(El Nio) about one year later. However, the influence on ENSO transition induced by the IOB is stronger than that by the IOD. The SSTAs in the equatorial central-eastern Pacific in the coming year originate from subsurface temperature anomalies in the equatorial eastern Indian and western Pacific Ocean, induced by the IOB and IOD through eastward and upward propagation to meet the surface. During this process, however the contribution of the oceanic channel process between the tropical Indian and Pacific oceans is totally different for the IOB and IOD. For the IOD, the influence of the Indonesian Throughflow transport anomalies could propagate to the eastern Pacific to induce the ENSO transition. For the IOB, the impact of the oceanic channel stays and disappears in the western Pacific without propagation to the eastern Pacific. 相似文献
18.
This study investigates the influences of tropical Indian Ocean(TIO) warming on tropical cyclone(TC)genesis in different regions of the western North Pacific(WNP) from July to October(JASO) during the decaying El Nio. The results show significant negative TC frequency anomalies localized in the southeastern WNP. Correlation analysis indicates that a warm sea surface temperature anomaly(SSTA) in the TIO strongly suppresses TC genesis south of 21°N and east of 140°E in JASO. Reduced TC genesis over the southeastern WNP results from a weak monsoon trough and divergence and subsidence anomalies associated with an equatorial baroclinic Kelvin wave. Moreover,suppressed convection in response to a cold local SSTA, induced by the increased northeasterly connected by the wind-evaporation-SST positive feedback mechanism, is found unfavorable for TC genesis. Positive TC genesis anomalies are observed over higher latitudinal regions(at around 21°N, 140°E) and the western WNP because of enhanced convection along the northern flank of the WNP anomalous anticyclone and low-level convergence,respectively. Although local modulation(e.g., local SST) could have greater dominance over TC activity at higher latitudes in certain anomalous years(e.g., 1988), a warm TIO SSTA can still suppress TC genesis in lower latitudinal regions of the WNP. A better understanding of the contributions of TIO warming could help improve seasonal TC predictions over different regions of the WNP in years of decaying El Nio. 相似文献
19.
The tropical Pacific has begun to experience a new type of El Nio, which has occurred particularly frequently during the last decade, referred to as the central Pacific(CP) El Nio. Various coupled models with different degrees of complexity have been used to make real-time El Nio predictions, but high uncertainty still exists in their forecasts. It remains unknown as to how much of this uncertainty is specifically related to the new CP-type El Nio and how much is common to both this type and the conventional Eastern Pacific(EP)-type El Nio. In this study, the deterministic performance of an El Nio–Southern Oscillation(ENSO) ensemble prediction system is examined for the two types of El Nio. Ensemble hindcasts are run for the nine EP El Nio events and twelve CP El Nio events that have occurred since 1950. The results show that(1) the skill scores for the EP events are significantly better than those for the CP events, at all lead times;(2) the systematic forecast biases come mostly from the prediction of the CP events; and(3) the systematic error is characterized by an overly warm eastern Pacific during the spring season, indicating a stronger spring prediction barrier for the CP El Nio. Further improvements to coupled atmosphere–ocean models in terms of CP El Nio prediction should be recognized as a key and high-priority task for the climate prediction community. 相似文献
20.
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 Nio episodes in the central Pacific and their delayed impacts on the following early summertime climate anomalies of eastern China were analyzed. The possible physical progres... 相似文献