How Many ENSO Flavors Can We Distinguish?*

2013 ◽  
Vol 26 (13) ◽  
pp. 4816-4827 ◽  
Author(s):  
Nathaniel C. Johnson
Keyword(s):  
El Niño ◽  
El Nino ◽  
Warm Pool ◽  
Tropical Pacific ◽  
La Niña ◽  
Western Pacific ◽  
Western Pacific Warm Pool ◽  
La Nina ◽  
Pacific Warm Pool ◽  
Sst Anomalies

Abstract It is now widely recognized that El Niño–Southern Oscillation (ENSO) occurs in more than one form, with the canonical eastern Pacific (EP) and more recently recognized central Pacific (CP) ENSO types receiving the most focus. Given that these various ENSO “flavors” may contribute to climate variability and long-term trends in unique ways, and that ENSO variability is not limited to these two types, this study presents a framework that treats ENSO as a continuum but determines a finite maximum number of statistically distinguishable representative ENSO patterns. A neural network–based cluster analysis called self-organizing map (SOM) analysis paired with a statistical distinguishability test determines nine unique patterns that characterize the September–February tropical Pacific SST anomaly fields for the period from 1950 through 2011. These nine patterns represent the flavors of ENSO, which include EP, CP, and mixed ENSO patterns. Over the 1950–2011 period, the most significant trends reflect changes in La Niña patterns, with a shift in dominance of La Niña–like patterns with weak or negative western Pacific warm pool SST anomalies until the mid-1970s, followed by a dominance of La Niña–like patterns with positive western Pacific warm pool SST anomalies, particularly after the mid-1990s. Both an EP and especially a CP El Niño pattern experienced positive frequency trends, but these trends are indistinguishable from natural variability. Overall, changes in frequency within the ENSO continuum contributed to the pattern of tropical Pacific warming, particularly in the equatorial eastern Pacific and especially in relation to changes of La Niña–like rather than El Niño–like patterns.

Variability of the western Pacific warm pool structure associated with El Niño

2016 ◽  
Vol 49 (7-8) ◽  
pp. 2431-2449 ◽  
Author(s):  
Shijian Hu ◽  
Dunxin Hu ◽  
Cong Guan ◽  
Nan Xing ◽  
Jianping Li ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Warm Pool ◽  
Western Pacific ◽  
Western Pacific Warm Pool ◽  
Pacific Warm Pool ◽  
The Western Pacific

A Common Base Mode of Asian Summer Monsoon Variability across Timescales

2021 ◽  
pp. 1-38
Author(s):  
Xudong Wang ◽  
Shang-Ping Xie ◽  
Zhaoyong Guan ◽  
Minyang Wang
Keyword(s):  
Summer Monsoon ◽  
El Niño ◽  
El Nino ◽  
Asian Summer Monsoon ◽  
Warm Pool ◽  
Western Pacific ◽  
Western Pacific Warm Pool ◽  
Monsoon Variability ◽  
Pacific Warm Pool ◽  
Asian Summer

AbstractThe summer intraseasonal oscillation (ISO) is characterized by a northward-moving rain band in the Indo-western Pacific warm pool region. Physical origin of the ISO is not fully understood, masked by strong interaction of convection and circulation. This study examines intraseasonal to interannual variability during June to August over the Indo-western Pacific warm pool region. The results show that the tropical Northwest Pacific anomalous anticyclone (NWP-AAC) is a fundamental mode on both intraseasonal and interannual timescales, destabilized by the monsoon mean state, specifically through barotropic energy conversion and convective feedback in the low-level confluence between the monsoon westerlies and easterly trade winds. On the interannual timescale, the NWP-AAC shows a biennial tendency, reversing phase from the summer of El Niño to the summer that follows; the AAC in post-El Niño summer is excited indirectly through sea surface temperature anomalies in the Indo-NWP. On the intraseasonal timescale, the column-integrated moisture advection causes the NWP-AAC-related convection propagates northward. Our results provide a unifying view of multi-scale Asian summer monsoon variability, with important implications for subseasonal to seasonal prediction.

scholarly journals Impacts of Two Types of El Niño and La Niña Events on Typhoon Activity

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Po-Chun Hsu ◽  
Chung-Ru Ho ◽  
Shin-Jye Liang ◽  
Nan-Jung Kuo
Keyword(s):  
Correlation Coefficient ◽  
El Niño ◽  
El Nino ◽  
Warm Pool ◽  
La Niña ◽  
El Niño Modoki ◽  
La Nina ◽  
Pacific Warm Pool ◽  
Highly Correlated ◽  
Hadley Centre

The HadISST (Hadley Centre Sea Ice and Sea Surface Temperature) dataset is used to define the years of El Niño, El Niño Modoki, and La Niña events and to find out the impacts of these events on typhoon activity. The results show that the formation positions of typhoon are farther eastward moving in El Niño years than in La Niña years and much further eastward in El Niño Modoki years. The lifetime and the distance of movement are longer, and the intensity of typhoons is stronger in El Niño and in El Niño Modoki years than in La Niña years. The Accumulated Cyclone Energy of typhoon is highly correlated with the Oceanic Niño Index with a correlation coefficient of 0.79. We also find that the typhoons anomalously decrease during El Niño years but increase during El Niño Modoki years. Besides, there are two types of El Niño Modoki, I and II. The intensity of typhoon in El Niño Modoki I years is stronger than in El Niño Modoki II years. Furthermore, the centroid position of the Western Pacific Warm Pool is strongly related to the area of typhoon formation with a correlation coefficient of 0.95.

scholarly journals Contribution of Synoptic Transients to the Potential Predictability of PNA Circulation Anomalies: El Niño versus La Niña

2015 ◽  
Vol 28 (21) ◽  
pp. 8347-8362 ◽  
Author(s):  
Muhammad Adnan Abid ◽  
In-Sik Kang ◽  
Mansour Almazroui ◽  
Fred Kucharski
Keyword(s):  
El Niño ◽  
El Nino ◽  
Signal To Noise Ratio ◽  
Tropical Pacific ◽  
La Niña ◽  
Potential Predictability ◽  
La Nina ◽  
The Pacific ◽  
Circulation Anomalies ◽  
Sst Anomalies

Abstract The potential predictability (PP) of seasonal-mean 200-hPa geopotential height (Z200) anomalies in the Pacific–North American (PNA) region is examined for El Niño and La Niña separately by using 50 ensemble members of twentieth-century AGCM simulations. Observed sea surface temperature (SST) is prescribed for the period 1870–2009, and 14 El Niño and La Niña years after 1900 are selected for the present study. The domain-averaged value of PP for Z200 in the PNA region, as measured by the signal-to-noise ratio, for El Niño is about 60% larger than that of La Niña. Such a large PP is mainly due to a larger signal and partly to less noise during El Niño compared to that during La Niña . The transient eddy feedback to the PNA circulation anomalies is stronger during El Niño events (about 50%) than that during La Niña, and this difference in the transients contributes significantly to the different Z200 signals in the PNA region. The noise variance of the transients during El Niño is about 17% smaller than during La Niña, and thus transients play an important role in the reduction of Z200 noise during El Niño. Idealized experiments with the same spatial pattern but different signs of SST anomalies confirm the results mentioned above. Moreover, these experiments with several different amplitudes of positive and negative phases of tropical Pacific SST anomalies show that signals of Z200 and transients are proportional to precipitation anomalies in the tropical Pacific, and noises of Z200 for El Niño cases are somewhat smaller than the corresponding values of La Niña.

scholarly journals The role of the South Pacific in modulating Tropical Pacific variability

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Christine T. Y. Chung ◽  
Scott B. Power ◽  
Arnold Sullivan ◽  
François Delage
Keyword(s):  
El Niño ◽  
Decadal Variability ◽  
El Nino ◽  
South Pacific ◽  
Tropical Pacific ◽  
Equatorial Pacific ◽  
La Niña ◽  
The South ◽  
La Nina ◽  
Sst Anomalies

AbstractTropical Pacific variability (TPV) heavily influences global climate, but much is still unknown about its drivers. We examine the impact of South Pacific variability on the modes of TPV: the El Niño-Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO). We conduct idealised coupled experiments in which we suppress temperature and salinity variability at all oceanic levels in the South Pacific. This reduces decadal variability in the equatorial Pacific by ~30% and distorts the spatial pattern of the IPO. There is little change to overall interannual variability, however there is a decrease in the magnitude of the largest 5% of both El Niño and La Niña sea-surface temperature (SST) anomalies. Possible reasons for this include: (i) reduced decadal variability means that interannual SST variability is superposed onto a ‘flatter’ background signal, (ii) suppressing South Pacific variability leads to the alteration of coupled processes linking the South and equatorial Pacific. A small but significant mean state change arising from the imposed suppression may also contribute to the weakened extreme ENSO SST anomalies. The magnitude of both extreme El Niño and La Niña SST anomalies are reduced, and the associated spatial patterns of change of upper ocean heat content and wind stress anomalies are markedly different for both types of events.

A Study of the Impact of Off-Equatorial Warm Pool SST Anomalies on ENSO Cycles

2005 ◽  
Vol 18 (2) ◽  
pp. 274-286 ◽  
Author(s):  
Amy Solomon ◽  
Fei-Fei Jin
Keyword(s):  
El Niño ◽  
El Nino ◽  
Coupled Model ◽  
Warm Pool ◽  
Western Pacific ◽  
Sea Surface ◽  
Pacific Warm Pool ◽  
The Impact ◽  
The Western Pacific ◽  
Sst Anomalies

Abstract Concurrent with most large El Niño events, cold sea surface temperature (SST) anomalies are observed over the western Pacific warm pool region (WPWP). Observational evidence that SST anomalies that form in the off-equatorial western Pacific during El Niño–Southern Oscillation (ENSO) cycles are forced by subsurface ocean processes equatorward of 12°N and air–sea fluxes poleward of 12°N is presented. It is demonstrated that diurnal mixing in the ocean equatorward of 12°N plays a significant role in bringing subsurface temperature anomalies to the sea surface during an El Niño event. The role of SST anomalies equatorward of 12°N in ENSO cycles is tested in the Zebiak–Cane coupled model, modified to allow for the impact of subsurface temperatures on SSTs. This coupled model successfully simulates cold SST anomalies in the off-equatorial northwestern Pacific that are observed to occur during the warm phase of ENSO and the atmospheric response to these anomalies, which is composed of both westerlies in the central Pacific and easterlies in the far western equatorial Pacific. It is found that there is little net change in the zonal mean wind stress at the equator, suggesting that the westerlies cancel the impact of the easterlies on the basin-scale tilt of the equatorial zonal mean thermocline depth. The anomalous westerly winds in the central equatorial Pacific are found to increase the amplitude of an El Niño event directly by increasing anomalous warm zonal advection and reducing upwelling. Moreover, the off-equatorial anticyclonic wind stress associated with the cold SST anomalies during the warm phase of ENSO tends to reduce the discharge of the equatorial heat content. Thus, the coupled processes over the western Pacific warm pool can serve as a positive feedback to amplify ENSO cycles.

scholarly journals Changes in Spread and Predictability Associated with ENSO in an Ensemble Coupled GCM

2006 ◽  
Vol 19 (17) ◽  
pp. 4378-4396 ◽  
Author(s):  
Renguang Wu ◽  
Ben P. Kirtman
Keyword(s):  
Surface Pressure ◽  
El Niño ◽  
El Nino ◽  
Tropical Pacific ◽  
La Niña ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Central Pacific ◽  
La Nina ◽  
Signal Change

Abstract The present study documents the influence of El Niño and La Niña events on the spread and predictability of rainfall, surface pressure, and 500-hPa geopotential height, and contrasts the relative contribution of signal and noise changes to the predictability change based on a long-term integration of an interactive ensemble coupled general circulation model. It is found that the pattern of the El Niño–Southern Oscillation (ENSO)-induced noise change for rainfall follows closely that of the corresponding signal change in most of the tropical regions. The noise for tropical Pacific surface pressure is larger (smaller) in regions of lower (higher) mean pressure. The ENSO-induced noise change for 500-hPa height displays smaller spatial scales compared to and has no systematic relationship with the signal change. The predictability for tropical rainfall and surface pressure displays obvious contrasts between the summer and winter over the Bay of Bengal, the western North Pacific, and the tropical southwestern Indian Ocean. The predictability for tropical 500-hPa height is higher in boreal summer than in boreal winter. In the equatorial central Pacific, the predictability for rainfall is much higher in La Niña years than in El Niño years. This occurs because of a larger percent reduction in the amplitude of noise compared to the percent decrease in the magnitude of signal from El Niño to La Niña years. A consistent change is seen in the predictability for surface pressure near the date line. In the western North and South Pacific, the predictability for boreal winter rainfall is higher in El Niño years than in La Niña years. This is mainly due to a stronger signal in El Niño years compared to La Niña years. The predictability for 500-hPa height increases over most of the Tropics in El Niño years. Over western tropical Pacific–Australia and East Asia, the predictability for boreal winter surface pressure and 500-hPa height is higher in El Niño years than in La Niña years. The predictability change for 500-hPa height is primarily due to the signal change.

scholarly journals Role of the Indo-Pacific Interbasin Coupling in Predicting Asymmetric ENSO Transition and Duration

2012 ◽  
Vol 25 (9) ◽  
pp. 3321-3335 ◽  
Author(s):  
Masamichi Ohba ◽  
Masahiro Watanabe
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
La Nina ◽  
The Pacific ◽  
Enso Asymmetry ◽  
Sst Anomalies

Warm and cold phases of El Niño–Southern Oscillation (ENSO) exhibit a significant asymmetry in their transition/duration such that El Niño tends to shift rapidly to La Niña after the mature phase, whereas La Niña tends to persist for up to 2 yr. The possible role of sea surface temperature (SST) anomalies in the Indian Ocean (IO) in this ENSO asymmetry is investigated using a coupled general circulation model (CGCM). Decoupled-IO experiments are conducted to assess asymmetric IO feedbacks to the ongoing ENSO evolution in the Pacific. Identical-twin forecast experiments show that a coupling of the IO extends the skillful prediction of the ENSO warm phase by about one year, which was about 8 months in the absence of the IO coupling, in which a significant drop of the prediction skill around the boreal spring (known as the spring prediction barrier) is found. The effect of IO coupling on the predictability of the Pacific SST is significantly weaker in the decay phase of La Niña. Warm IO SST anomalies associated with El Niño enhance surface easterlies over the equatorial western Pacific and hence facilitate the El Niño decay. However, this mechanism cannot be applied to cold IO SST anomalies during La Niña. The result of these CGCM experiments estimates that approximately one-half of the ENSO asymmetry arises from the phase-dependent nature of the Indo-Pacific interbasin coupling.

scholarly journals Indo-Western Pacific Climate Variability: ENSO Forcing and Internal Dynamics in a Tropical Pacific Pacemaker Simulation

2018 ◽  
Vol 31 (24) ◽  
pp. 10123-10139 ◽  
Author(s):  
Chuan-Yang Wang ◽  
Shang-Ping Xie ◽  
Yu Kosaka
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
Internal Variability ◽  
Tropical Pacific ◽  
Western Pacific ◽  
Ocean Atmosphere ◽  
Sst Anomalies

El Niño–Southern Oscillation (ENSO) peaks in boreal winter but its impact on Indo-western Pacific climate persists for another two seasons. Key ocean–atmosphere interaction processes for the ENSO effect are investigated using the Pacific Ocean–Global Atmosphere (POGA) experiment with a coupled general circulation model, where tropical Pacific sea surface temperature (SST) anomalies are restored to follow observations while the atmosphere and oceans are fully coupled elsewhere. The POGA shows skills in simulating the ENSO-forced warming of the tropical Indian Ocean and an anomalous anticyclonic circulation pattern over the northwestern tropical Pacific in the post–El Niño spring and summer. The 10-member POGA ensemble allows decomposing Indo-western Pacific variability into the ENSO forced and ENSO-unrelated (internal) components. Internal variability is comparable to the ENSO forcing in magnitude and independent of ENSO amplitude and phase. Random internal variability causes apparent decadal modulations of ENSO correlations over the Indo-western Pacific, which are high during epochs of high ENSO variance. This is broadly consistent with instrumental observations over the past 130 years as documented in recent studies. Internal variability features a sea level pressure pattern that extends into the north Indian Ocean and is associated with coherent SST anomalies from the Arabian Sea to the western Pacific, suggestive of ocean–atmosphere coupling.

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