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In this study, we evaluate the intensity of the Central‐Pacific (CP) and Eastern‐Pacific (EP) types of El Niño‐Southern Oscillation (ENSO) simulated in the pre‐industrial, historical, and the Representative Concentration Pathways (RCP) 4.5 experiments of the Coupled Model Intercomparison Project Phase 5 (CMIP5). Compared to the CMIP3 models, the pre‐industrial simulations of the CMIP5 models are found to (1) better simulate the observed spatial patterns of the two types of ENSO and (2) have a significantly smaller inter‐model diversity in ENSO intensities. The decrease in the CMIP5 model discrepancies is particularly obvious in the simulation of the EP ENSO intensity, although it is still more difficult for the models to reproduce the observed EP ENSO intensity than the observed CP ENSO intensity. Ensemble means of the CMIP5 models indicate that the intensity of the CP ENSO increases steadily from the pre‐industrial to the historical and the RCP4.5 simulations, but the intensity of the EP ENSO increases from the pre‐industrial to the historical simulations and then decreases in the RCP4.5 projections. The CP‐to‐EP ENSO intensity ratio, as a result, is almost the same in the pre‐industrial and historical simulations but increases in the RCP4.5 simulation. Key Points Smaller inter‐model diversity of ENSO intensities in CMIP5 than in CMIP3 Decrease in the diversity is particularly significant for the simulated EP ENSO Different response of EP and CP ENSO to global warming

Much understanding of the El Niño‐Southern Oscillation (ENSO) has been obtained from the analyses of the climate simulations produced for World Climate Research Programme's Coupled Model Intercomparison Project phase 3 (CMIP3). However, most of these analyses do not consider the existence of the Eastern‐Pacific (EP) and Central‐Pacific (CP) types of ENSO events, which have been increasingly recognized as two distinct types of interannual sea surface temperature (SST) variation in the tropical Pacific. This study uses a regression‐Empirical Orthogonal Function method to identify how well these two ENSO types are captured in the pre‐industrial simulations of nineteen CMIP3 models. It is concluded that most CMIP3 models (13 out of 19) can produce realistically strong CP ENSOs, but only a few of them (9 out of 19) can produce realistically strong EP ENSOs. Six models that realistically simulate both the EP and CP ENSOs and their intensity ratio are identified. By separating the SST variability into these two types, it is further revealed that the leading periodicity of the simulated EP ENSO is linearly related to the latitudinal width of SST variability and varies from 1 to 5 years. As for the simulated CP ENSO, its leading periodicity is either 2 or 4 years depending on whether its SST variability is located to the east of the dateline or in the western‐Pacific warm pool, respectively. The identification produced in this study offers useful information to further understand the two types of ENSO using the CMIP3 models.

Asymmetric atmospheric responses to ENSO are revisited after dividing it into two types: eastern-Pacific (EP) and central-Pacific (CP) ENSO. The EP ENSO triggers two obvious asymmetric atmospheric teleconnections: One is the Pacific–North American-like teleconnection. Its asymmetry is characterized by weaker amplitudes during the EP La Niña than EP El Niño, which is caused by a much weaker EP La Niña tropical forcing and the resultant weaker extra-tropical vorticity forcing. The other is the Atlantic–Eurasian teleconnection with negative height anomalies in the subtropical Atlantic and Eurasia and positive anomalies in the high-latitude Atlantic and northeast Asia, which appears during the EP La Niña but not during the EP El Niño. The background state plays a vital role in this asymmetry. The EP La Niña-type basic state is more conducive to propagation of the wave rays into the Atlantic–Eurasian region compared to EP El Niño situation. In contrast, the CP ENSO yields an Arctic Oscillation-like teleconnection, presenting an appreciable asymmetry in the subtropical amplitudes that are stronger during the CP El Niño than during the CP La Niña. In this case, the distinct effects of the different background state on the equatorward wave rays are responsible for this asymmetry. Under the CP El Niño-type background state, the equatorward wave rays tend to be reflected at the latitudes where the zonal wind equals zero (U = 0), and then successfully captured by the subtropical westerly jet. However, under the CP La Niña-type background state, the equatorward wave rays disappear at U = 0 latitudes.

In this study, we evaluated the predictability of the two flavors of the El Niño Southern Oscillation (ENSO) based on a long-term retrospective prediction from 1881 to 2017 with the Community Earth System Model. Specifically, the Central-Pacific (CP) ENSO has a more obvious Spring Predictability Barrier and lower deterministic prediction skill than the Eastern-Pacific (EP) ENSO. The potential predictability declines with lead time for both the two flavors of ENSO, and the EP ENSO has a higher upper limit of the prediction skill as compared with the CP ENSO. The predictability of the two flavors of ENSO shows distinct interdecadal variation for both actual skill and potential predictability; however, their trends in the predictability are not synchronized. The signal component controls the seasonal and interdecadal variations of predictability for the two flavors of ENSO, and has larger contribution to the CP ENSO than the EP ENSO. There is significant scope for improvement in predicting the two flavors of ENSO, especially for the CP ENSO.

Variability of extreme temperatures has an important influence on sensitive ecosystem and human activities on the Tibetan Plateau (TP). Nevertheless, the uncertainties of different El Niño-Southern Oscillation (ENSO) effects on extreme temperatures over the TP are poorly understood. Thus, this study focuses on variations in temperature extremes across the TP during 1980–2020 based on the daily maximum temperature and minimum temperature. We quantitatively examine the effects of different ENSO phases and related large-scale atmospheric circulation anomalies on the changes in temperature extremes according to different ENSO phases. The results show that the number of extreme cold events decreased significantly on the TP, while the number of extreme warm events increased significantly from 1980 to 2020. Moreover, our results suggest that the response of temperature extremes differs between the Eastern Pacific (EP) and Central Pacific (CP) ENSO. In particular, EP El Niño episodes result in more extreme cold events (r = 0.36, P < 0.01), whereas the influence of the CP El Niño episodes on the temperature extreme over the TP is weak. The correlation coefficients between the CP ENSO index and daily minimum temperature (daily maximum temperature) are 0.46 (0.49). In addition, the developing and decaying phases of ENSO had an essential influence on temperature extreme variability on the TP through the modulation of large-scale atmospheric circulation anomalies. Sea surface temperature during the different ENSO phases induced a Walker circulation anomaly in the tropical Pacific and ascending motion over the tropical Indian Ocean, which contributes to the generation of the anomalies of wind and geopotential height around the TP, inducing non-uniform responses of temperature extremes over the TP. In conclusion, ENSO is a critical factor that influences temperature extremes on the TP. This study provides some insight into understanding the dynamics of regional extreme temperatures during different ENSO episodes.

New Caledonia (NC; ∼166°E, 22°S) rainfall anomalies are more sensitive to central Pacific (CP) El Niño and La Niña events than to those exhibiting highest sea surface temperature (SST) anomalies in the eastern Pacific (EP). The linear relationship between NC rainfall anomalies and CP SST indices peaks from September to March (S–M). The seasonal S–M atmospheric anomalies observed in the South West (SW) Pacific during the warm CP events are highly dissimilar to the EP ones, while there are more similarities during the cold events with a higher amplitude during the CP ones. The warm CP events strengthen the southern Hadley cell around NC longitudes, with positive rainfall anomalies in the equatorial Pacific leading to an anomalous release of latent heat in the upper troposphere and an increased subsidence in the SW Pacific. Atmospheric anomalies are strongest in September–November because of a combination of a rather strong zonal SST gradient with the warmest SST in the equatorial Pacific just west of the dateline. The cold CP and EP events are associated with a southwestward shift of the South Pacific Convergence Zone with strongest atmospheric anomalies during the CP events. Squared wavelet coherence between NC rainfall and Niño 4 SST index shows that their negative correlations are mostly carried by two distinct timescales: the classical El Niño–Southern Oscillation (i.e., 3–6 years) variability and a quasi‐decadal one (i.e., 10–12 years). The high‐frequency (>1/8 cycle per year) correlations peak around Christmas and are quasi‐stationary since 1950, whereas the low‐frequency ones (<1/8 cycle per year) peak from the austral autumn to the austral spring and have strengthened from ∼1975 to 1980 onward with a subtle warming trend in the equatorial Pacific near the dateline. Key Points Seasonal relationships between ENSO and New Caledonia (NC) rainfall anomalies Central Pacific vs. eastern Pacific El Nino impacts on NC rainfall Temporal modulation of the ENSO‐NC rainfall anomalies relationships

This study focuses on the interdecadal changes in ENSO properties emerging around the year 2000. Compared to 1980-1999, after 2000, the ENSO amplitude weakened, the occurrence of the central Pacific (CP) El Niño increased, and the eastern Pacific (EP) El Niño became suppressed. Meanwhile, the dominant period of ENSO shortened from quasi-quadrennial (QQ) to quasi-biennial (QB). The authors show that these changes in ENSO properties are evidently consistent with the change in the stability of the ENSO mode through connecting the two ENSO types with the two coupled ENSO modes, i.e. the QQ and QB modes. It is suggested that the relative activity or stability of the two ENSO modes changed after the year 2000. The intensity of both the QQ and QB mode weakened. The QQ mode, which is linked to EP ENSO and was significantly strong during 1980-1999, became much weaker after 2000 in terms of the EP type almost disappearing. Compared with the weakness of the QQ mode, the QB mode, as manifested by the CP type, remained active and became dominant in the tropical Pacific after 2000. Analysis shows that the changes in mean states in the tropical Pacific were likely responsible for the interdecadal ENSO changes around the year 2000.

We provide photographic evidence for eight fish species from five families, not previously seen within the Galápagos Marine Reserve. Four species are native to the Central Tropical Pacific and likely arrived during recent El Niño phenomena: Acanthurus leucocheilus Herre, 1927, Acanthurus olivaceus Bloch & Schneider, 1801, Naso hexacanthus (Bleeker, 1855), and Chaetodon punctatofasciatus Cuvier, 1831. One is a pantropical species: Kyphosus sectatrix (Linnaeus, 1758). The remaining species likely originated within the Eastern Tropical Pacific: Ctenochaetus marginatus (Valenciennes, 1835), Halichoeres malpelo Allen & Robertson, 1992, and Gymnothorax porphyreus (Guichenot, 1848).

Atmospheric blocking events are persistent quasi‐stationary geopotential height anomalies that divert the jet stream from its climatological path in the mid‐ to high‐latitudes. Previous studies have found that different phases of the El Niño–Southern Oscillation (ENSO) influence the characteristics of blocking, but none have considered the spatial diversity of El Niño. In this study, we examine Northern Hemisphere blocking events with respect to the “Central Pacific” (CP) and “Eastern Pacific” (EP) flavors of El Niño in 83 years of ERA5 reanalysis. The two El Niño flavors have dissimilar patterns of forcing on atmospheric circulation that impact the strength and placement of the upper‐level jet stream, thus affecting blocking event frequency and duration. Significant contrasts in blocking characteristics between CP and EP years are disregarded when a single ENSO index is used, and we emphasize that El Niño flavors should be considered in future investigations of blocking and ENSO‐related variability. Plain Language Summary Persistent, large‐scale weather phenomena known as atmospheric blocking events divert the jet streams in the mid‐ to high‐latitudes from their typical paths, often leading to extreme weather events. Tropical climate variations such as the El Niño–Southern Oscillation (ENSO) affect global atmospheric circulation and weather including the occurrence and features of blocking events. The warm phase of ENSO, El Niño, has two main “flavors” of variability designated by the location of the peak sea surface temperature anomalies in either the Central Pacific (“CP”) or Eastern Pacific (“EP”), and each flavor has unique global impacts. We found that the relationships between El Niño flavors and Northern Hemisphere blocking characteristics in eight decades of observational data (reanalysis) differ significantly from each other, and that these explicit contrasts are overlooked when El Niño is defined by a single ENSO index. These results have the potential to improve the predictability of blocking events during El Niño years and enhance confidence in projections of blocking under climate change conditions. Key Points El Niño–Southern Oscillation (ENSO) indices that neglect El Niño diversity confound the unique signals of Eastern Pacific (EP) and Central Pacific (CP) changes in NH blocking events North Pacific wintertime blocking frequency is reduced in EP Niño, while the region of blocking shifts northeast during CP Niño EP‐year blocking events are shorter than CP‐year blocks in the North Pacific

The 1925 El Niño (EN) event was the third strongest in the twentieth century according to its impacts in the far-eastern Pacific (FEP) associated with severe rainfall and flooding in coastal northern Peru and Ecuador in February–April 1925. In this study we gathered and synthesised a large diversity of in situ observations to provide a new assessment of this event from a modern perspective. In contrast to the extreme 1982–1983 and 1997–1998 events, this very strong “coastal El Niño” in early 1925 was characterised by warm conditions in the FEP, but cool conditions elsewhere in the central Pacific. Hydrographic and tide-gauge data indicate that downwelling equatorial Kelvin waves had little role in its initiation. Instead, ship data indicate an abrupt onset of strong northerly winds across the equator and the strengthening/weakening of the intertropical convergence zones (ITCZ) south/north of the equator. Observations indicate lack of external atmospheric forcing by the Panama gap jet and the south Pacific anticyclone and suggest that the coupled ocean–atmosphere feedback dynamics associated with the ITCZs, northerly winds, and the north–south SST asymmetry in the FEP lead to the enhancement of the seasonal cycle that produced this EN event. We propose that the cold conditions in the western-central equatorial Pacific, through its teleconnection effects on the FEP, helped destabilize the ITCZ and enhanced the meridional ocean–atmosphere feedback, as well as helping produce the very strong coastal rainfall. This is indicated by the nonlinear relation between the Piura river record at 5°S and the SST difference between the FEP and the western-central equatorial Pacific, a stability proxy. In summary, there are two types of EN events with very strong impacts in the FEP, both apparently associated with nonlinear convective feedbacks but with very different dynamics: the very strong warm ENSO events like 1982–1983 and 1997–1998, and the very strong “coastal” EN events like 1925.