scholarly journals A Nonlinear Analysis of the ENSO Cycle and Its Interdecadal Changes*

2005 ◽  
Vol 18 (16) ◽  
pp. 3229-3239 ◽  
Author(s):  
Soon-Il An ◽  
William W. Hsieh ◽  
Fei-Fei Jin
Keyword(s):  
El Niño ◽  
El Nino ◽  
Heat Content ◽  
Principal Component ◽  
Equatorial Region ◽  
La Niña ◽  
Enso Cycle ◽  
Heat Accumulation ◽  
Neural Network Approach ◽  
La Nina

Abstract The nonlinear principal component analysis (NLPCA), via a neural network approach, was applied to thermocline anomalies in the tropical Pacific. While the tropical sea surface temperature (SST) anomalies had been nonlinearly mapped by the NLPCA mode 1 onto an open curve in the data space, the thermocline anomalies were mapped to a closed curve, suggesting that ENSO is a cyclic phenomenon. The NLPCA mode 1 of the thermocline anomalies reveals the nonlinear evolution of the ENSO cycle with much asymmetry for the different phases: The weak heat accumulation in the whole equatorial Pacific is followed by the strong El Niño, and the subsequent strong drain of equatorial heat content toward the off-equatorial region precedes a weak La Niña. This asymmetric ENSO evolution implies that the nonlinear instability enhances the growth of El Niño, but dwarfs the growth of La Niña. The nonlinear ENSO cycle was found to have changed since the late 1970s. For the pre-1980s the ENSO cycle associated with the thermocline is less asymmetrical than that during the post-1980s, indicating that the nonlinearity of the ENSO cycle has become stronger since the late 1970s.

Sea Surface Temperature in the Subtropical Pacific Boosted the 2015 El Niño and Hindered the 2016 La Niña

2018 ◽  
Vol 31 (2) ◽  
pp. 877-893 ◽  
Author(s):  
Jingzhi Su ◽  
Renhe Zhang ◽  
Xinyao Rong ◽  
Qingye Min ◽  
Congwen Zhu
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
El Niño ◽  
El Nino ◽  
Heat Content ◽  
Equatorial Region ◽  
La Niña ◽  
Sea Surface ◽  
La Nina ◽  
Super El Niño

After the quick decaying of the 2015 super El Niño, the predicted La Niña unexpectedly failed to materialize to the anticipated standard in 2016. Diagnostic analyses, as well as numerical experiments, showed that this ENSO evolution of the 2015 super El Niño and the hindered 2016 La Niña may be essentially caused by sea surface temperature anomalies (SSTAs) in the subtropical Pacific. The self-sustaining SSTAs in the subtropical Pacific tend to weaken the trade winds during boreal spring–summer, leading to anomalous westerlies along the equatorial region over a period of more than one season. Such long-lasting wind anomalies provide an essential requirement for ENSO formation, particularly before a positive Bjerknes feedback is thoroughly built up between the oceanic and atmospheric states. Besides the 2015 super El Niño and the hindered La Niña in 2016, there were several other El Niño and La Niña events that cannot be explained only by the oceanic heat content in the equatorial Pacific. However, the questions related to those eccentric El Niño and La Niña events can be well explained by suitable SSTAs in the subtropical Pacific. Thus, the leading SSTAs in the subtropical Pacific can be treated as an independent indicator for ENSO prediction, on the basis of the oceanic heat content inherent in the equatorial region. Because ENSO events have become more uncertain under the background of global warming and the Pacific decadal oscillation during recent decades, thorough investigation of the role of the subtropical Pacific in ENSO formation is urgently needed.

scholarly journals Mechanisms linking multi-year La Niña with preceding strong El Niño

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tomoki Iwakiri ◽  
Masahiro Watanabe
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Heat Content ◽  
Equatorial Pacific ◽  
La Niña ◽  
Ekman Transport ◽  
Enso Cycle ◽  
Easterly Wind ◽  
La Nina

AbstractEl Niño-Southern Oscillation (ENSO), characterized by anomalous sea surface temperature in the central-eastern equatorial Pacific, is a dominant interannual variability, impacting worldwide weather and socioeconomics. The ENSO cycle contains irregularity, in which La Niña often persists for more than two years, called “multi-year La Niña”. Observational records show that multi-year La Niña tends to accompany strong El Niño in the preceding year, but their physical linkage remains unclear. Here we show using reanalysis data that a strong El Niño excites atmospheric conditions that favor the generation of multi-year La Niña in subsequent years. Easterly wind anomalies along the northern off-equatorial Pacific during the decay phase of the strong El Niño are found crucial as they act to discharge ocean heat content (OHC) via an anomalous northward Ekman transport. The negative OHC anomaly is large enough to be restored by a single La Niña and, therefore, causes another La Niña to occur in the second year. Furthermore, analyses of the Coupled Model Intercomparison Project Phase 6 (CMIP6) climate models support the abovementioned mechanisms and indicate that the occurrence frequencies of multi-year La Niña and strong El Niño are highly correlated.

The Influence of the Indian Ocean on ENSO Stability and Flavor

2017 ◽  
Vol 30 (7) ◽  
pp. 2601-2620 ◽  
Author(s):  
Claudia E. Wieners ◽  
Henk A. Dijkstra ◽  
Will P. M. de Ruijter
Keyword(s):  
Indian Ocean ◽  
Spatial Pattern ◽  
El Niño ◽  
East Coast ◽  
El Nino ◽  
La Niña ◽  
Enso Cycle ◽  
Central Pacific ◽  
La Nina ◽  
The Indian Ocean

The effect of long-term trends and interannual, ENSO-driven variability in the Indian Ocean (IO) on the stability and spatial pattern of ENSO is investigated with an intermediate-complexity two-basin model. The Pacific basin is modeled using a fully coupled (i.e., generating its own background state) Zebiak–Cane model. IO sea surface temperature (SST) is represented by a basinwide warming pattern whose strength is constant or varies at a prescribed lag to ENSO. Both basins are coupled through an atmosphere transferring information between them. For the covarying IO SST, a warm IO during the peak of El Niño (La Niña) dampens (destabilizes) ENSO, and a warm IO during the transition from El Niño to La Niña (La Niña to El Niño) shortens (lengthens) the period. The influence of the IO on the spatial pattern of ENSO is small. For constant IO warming, the ENSO cycle is destabilized because stronger easterlies induce more background upwelling, more thermocline steepening, and a stronger Bjerknes feedback. The SST signal at the east coast weakens or reverses sign with respect to the main ENSO signal [i.e., ENSO resembles central Pacific (CP) El Niños]. This is due to a reduced sensitivity of the SST to thermocline variations in case of a shallow background thermocline, as found near the east coast for a warm IO. With these results, the recent increase in CP El Niño can possibly be explained by the substantial IO (and west Pacific) warming over the last decades.

scholarly journals Reexamining El Niño and Cholera in Peru: A Climate Affairs Approach

2013 ◽  
Vol 5 (2) ◽  
pp. 148-161 ◽  
Author(s):  
Iván J. Ramírez ◽  
Sue C. Grady ◽  
Michael H. Glantz
Keyword(s):  
El Niño ◽  
Elevated Temperatures ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
Enso Cycle ◽  
Holistic View ◽  
La Nina ◽  
Cholera Epidemic ◽  
The Impact

Abstract In the 1990s Peru experienced the first cholera epidemic after almost a century. The source of emergence was initially attributed to a cargo ship, but later there was evidence of an El Niño association. It was hypothesized that marine ecosystem changes associated with El Niño led to the propagation of V. cholerae along the coast of Peru, which in turn initiated the onset of the epidemic in 1991. Earlier studies supported this explanation by demonstrating a relationship between elevated temperatures and increased cholera incidence in Peru; however, other aspects of El Niño–Southern Oscillation (ENSO) and their potential impacts on cholera were not investigated. Therefore, this study examines the relationship between El Niño and cholera in Peru from a holistic view of the ENSO cycle. A “climate affairs” approach is employed as a conceptual framework to incorporate ENSO’s multidimensional nature and to generate new hypotheses about the ENSO and cholera association in Peru. The findings reveal that ENSO may have been linked to the cholera epidemic through multiple pathways, including rainfall extremes, La Niña, and social vulnerability, with impacts depending on the geography of teleconnections within Peru. When the definition of an ENSO event is examined, cholera appears to have emerged either during ENSO neutral or La Niña conditions. Furthermore, the analysis herein suggests that the impact of El Niño arrived much later, possibly resulting in heightened transmission in the austral summer of 1992. In conclusion, a modified hypothesis with these new insights on cholera emergence and transmission in Peru is presented.

scholarly journals The ENSO–Asian Monsoon Interaction in a Coupled Ocean–Atmosphere GCM

2007 ◽  
Vol 20 (20) ◽  
pp. 5164-5177 ◽  
Author(s):  
Ying Li ◽  
Riyu Lu ◽  
Buwen Dong
Keyword(s):  
El Niño ◽  
Asian Monsoon ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
Enso Cycle ◽  
Central Pacific ◽  
La Nina ◽  
Ocean Atmosphere ◽  
The Relationship

Abstract In this study, the authors evaluate the (El Niño–Southern Oscillation) ENSO–Asian monsoon interaction in a version of the Hadley Centre coupled ocean–atmosphere general circulation model (CGCM) known as HadCM3. The main focus is on two evolving anomalous anticyclones: one located over the south Indian Ocean (SIO) and the other over the western North Pacific (WNP). These two anomalous anticyclones are closely related to the developing and decaying phases of the ENSO and play a crucial role in linking the Asian monsoon to ENSO. It is found that the HadCM3 can well simulate the main features of the evolution of both anomalous anticyclones and the related SST dipoles, in association with the different phases of the ENSO cycle. By using the simulated results, the authors examine the relationship between the WNP/SIO anomalous anticyclones and the ENSO cycle, in particular the biennial component of the relationship. It is found that a strong El Niño event tends to be followed by a more rapid decay and is much more likely to become a La Niña event in the subsequent winter. The twin anomalous anticyclones in the western Pacific in the summer of a decaying El Niño are crucial for the transition from an El Niño into a La Niña. The El Niño (La Niña) events, especially the strong ones, strengthen significantly the correspondence between the SIO anticyclonic (cyclonic) anomaly in the preceding autumn and WNP anticyclonic (cyclonic) anomaly in the subsequent spring, and favor the persistence of the WNP anomaly from spring to summer. The present results suggest that both El Niño (La Niña) and the SIO/WNP anticyclonic (cyclonic) anomalies are closely tied with the tropospheric biennial oscillation (TBO). In addition, variability in the East Asian summer monsoon, which is dominated by the internal atmospheric variability, seems to be responsible for the appearance of the WNP anticyclonic anomaly through an upper-tropospheric meridional teleconnection pattern over the western and central Pacific.

scholarly journals An Alert Classification System for Monitoring and Assessing the ENSO Cycle

2007 ◽  
Vol 22 (2) ◽  
pp. 353-371 ◽  
Author(s):  
V. E. Kousky ◽  
R. W. Higgins
Keyword(s):  
El Niño ◽  
Classification System ◽  
Scientific Community ◽  
El Nino ◽  
La Niña ◽  
Enso Cycle ◽  
Intensity Scale ◽  
La Nina ◽  
Real Time Information ◽  
Time Information

Abstract An alert classification system for the ENSO cycle is introduced. The system includes watches, advisories, and a five-class intensity scale for warm and cold phases of the ENSO cycle. A watch is issued when conditions are favorable for the formation of an El Niño or La Niña within the next 6 months. An advisory is issued when El Niño or La Niña conditions are present, based on NOAA’s operational definitions. The intensity scale, referred to as the ENSO Intensity Scale (EIS), is used for operational and retrospective assessments of the intensity of warm (El Niño) and cold (La Niña) episodes, without being prescriptive concerning ENSO-related anomalies or impacts. The Climate Prediction Center’s (CPC’s) monthly Climate Diagnostics Bulletin and ENSO Diagnostic Discussions will serve as the primary vehicles for disseminating real-time information concerning the ENSO alert status to the scientific community and public at large. An objective method that relates the EIS to anomalies is used to assess the effects of warm and cold episodes. The method is illustrated using precipitation in the global Tropics and subtropics and in the conterminous United States. The methodology is quite general and can be used to relate the ENSO cycle to other quantities.

The mechanism of general flowering in Dipterocarpaceae in the Malay Peninsula

1999 ◽  
Vol 15 (4) ◽  
pp. 437-449 ◽  
Author(s):  
Masatoshi Yasuda ◽  
Jun Matsumoto ◽  
Noriyuki Osada ◽  
San'ei Ichikawa ◽  
Naoki Kachi ◽  
...  
Keyword(s):  
El Niño ◽  
Atmospheric Carbon Dioxide ◽  
El Nino ◽  
Meteorological Data ◽  
Equatorial Region ◽  
La Niña ◽  
Malay Peninsula ◽  
Night Time ◽  
La Nina ◽  
General Flowering

The mechanism of general flowering in Dipterocarpaceae in the Malay Peninsula is revealed through field survey and meteorological data analyses. The regions of general flowering coincide with those which experienced a low night-time temperature (LNT) c. 2 mo before flowering. This supports the hypothesis that low air temperature induces the development of floral buds of dipterocarps. LNT was found to be caused by radiative cooling during dry spells in winter when the northern subtropical ridge (STR) occasionally migrates southwards with a dry air mass into the equatorial region. LNT events usually occur in La Niña episodes, not in El Niño episodes as believed previously. This is because the southward migration of the STR is associated with the intensification of local meridional Hadley Circulation in the western Pacific, which is strengthened in a La Niña episode. Results suggest that El Niño-like climate change in increased atmospheric carbon dioxide concentrations may be critical for the tropical rain forest biome in south-east Asia.

scholarly journals ENSO and sandy beach macrobenthos of the tropical East Pacific: some speculations

2006 ◽  
Vol 6 ◽  
pp. 57-61 ◽  
Author(s):  
T. Vanagt ◽  
E. Beekman ◽  
M. Vincx ◽  
S. Degraer
Keyword(s):  
El Niño ◽  
Sandy Beach ◽  
El Nino ◽  
Water System ◽  
La Niña ◽  
Warm Water ◽  
Enso Cycle ◽  
Marine Biota ◽  
La Nina ◽  
Normal Period

Abstract. The influence of the ENSO cycle on marine fauna and flora has only recently been given the attention it deserves. The very strong 1997–1998 El Niño and its obvious effects on marine biota was a key point in ENSO research, but unfortunately few quantitative data about the 1997–1998 El Niño itself are available. To gather information about the effect of ENSO on the macrobenthos, we performed a bi-weekly transect monitoring on an Ecuadorian sandy beach in 2000–2001, during the strong La Niña following the 1997–1998 El Niño, and in the normal period of 2002–2004. In this paper, intertidal macrofaunal densities at higher taxonomic level are used to compare a La Niña phase with the 'normal' situation. The few existing documents about El Niño and sandy beach macrobenthos, and scattered data from previous and current research, were used to complete the picture. Total macrobenthos densities were 300% lower during the La Niña phase compared with equal months in the normal phase. Especially Crustacea and Mollusca showed a marked increase in densities towards the normal situation (94% and 341% respectively). Polychaeta and Echinodermata, however, showed higher densities during the La Niña phase (22% and 73% respectively). Two possible explanations are proposed. (1) Low densities during the La Niña could be due to the very strong preceding El Niño, suggesting the populations were still recovering. This hypothesis is supported by previous work done in the south of Peru. This is, however, a cold water system, compared to the Ecuadorian warm water system. (2) The second hypothesis states that a La Niña will have a very severe impact on the intertidal macrofauna of a warm water system like the Ecuadorian coast.

The Pacific’s Response to Surface Heating in 130 Yr of SST: La Niña–like or El Niño–like?

2010 ◽  
Vol 67 (8) ◽  
pp. 2649-2657 ◽  
Author(s):  
Ka-Kit Tung ◽  
Jiansong Zhou
Keyword(s):  
El Niño ◽  
Climate Model ◽  
El Nino ◽  
Walker Circulation ◽  
Dominant Mode ◽  
Equatorial Region ◽  
La Niña ◽  
Radiative Heating ◽  
Modified Method ◽  
La Nina

Abstract Using a modified method of multiple linear regression on instrumented sea surface temperature (SST) in the two longest historical datasets [the Extended Reconstructed SST dataset (ERSST) and the Met Office Hadley Centre Sea Ice and SST dataset (HadISST)], it is found that the response to increased greenhouse forcing is a warm SST in the mid- to eastern Pacific Ocean in the equatorial region in the annual or seasonal mean. The warming is robustly statistically significant at the 95% confidence level. Consistent with this, the smaller radiative heating from solar forcing produces a weak warming also in this region, and the spatial pattern of the response is neither La Niña–like nor El Niño–like. It is noted that previous reports of a cold-tongue (La Niña–like) response to increased greenhouse or to solar-cycle heating were likely caused by contaminations due to the dominant mode of natural response in the equatorial Pacific. The present result has implications on whether the Walker circulation is weakened or strengthened in a warmer climate and on coupled atmosphere–ocean climate model validation.

scholarly journals Simple stochastic model for El Niño with westerly wind bursts

2016 ◽  
Vol 113 (37) ◽  
pp. 10245-10250 ◽  
Author(s):  
Sulian Thual ◽  
Andrew J. Majda ◽  
Nan Chen ◽  
Samuel N. Stechmann
Keyword(s):  
El Niño ◽  
El Nino ◽  
Burst Activity ◽  
La Niña ◽  
Western Pacific ◽  
Enso Cycle ◽  
Modeling Framework ◽  
La Nina ◽  
Wind Bursts ◽  
The Western Pacific

Atmospheric wind bursts in the tropics play a key role in the dynamics of the El Niño Southern Oscillation (ENSO). A simple modeling framework is proposed that summarizes this relationship and captures major features of the observational record while remaining physically consistent and amenable to detailed analysis. Within this simple framework, wind burst activity evolves according to a stochastic two-state Markov switching–diffusion process that depends on the strength of the western Pacific warm pool, and is coupled to simple ocean–atmosphere processes that are otherwise deterministic, stable, and linear. A simple model with this parameterization and no additional nonlinearities reproduces a realistic ENSO cycle with intermittent El Niño and La Niña events of varying intensity and strength as well as realistic buildup and shutdown of wind burst activity in the western Pacific. The wind burst activity has a direct causal effect on the ENSO variability: in particular, it intermittently triggers regular El Niño or La Niña events, super El Niño events, or no events at all, which enables the model to capture observed ENSO statistics such as the probability density function and power spectrum of eastern Pacific sea surface temperatures. The present framework provides further theoretical and practical insight on the relationship between wind burst activity and the ENSO.

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