The extreme El Niño of 2015–2016: the role of westerly and easterly wind bursts, and preconditioning by the failed 2014 event

2017 ◽  
Vol 52 (12) ◽  
pp. 7339-7357 ◽  
Author(s):  
Shineng Hu ◽  
Alexey V. Fedorov
Keyword(s):  
El Niño ◽  
El Nino ◽  
Easterly Wind ◽  
Wind Bursts ◽  
Extreme El Niño

scholarly journals Role of Low-Frequency Wind Variability in Inducing WWBs during the onset of super El Niños

2021 ◽  
Author(s):  
Yi-Kai Wu ◽  
Chi-Cherng Hong ◽  
Tim Li ◽  
An-Yi Huang
Keyword(s):  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Low Frequency ◽  
Wind Fields ◽  
Wind Variability ◽  
The Pacific ◽  
Sst Anomaly ◽  
Wind Bursts

Abstract In this study, the effect of multiple timescale wind fields on the westerly wind bursts (WWBs) was investigated during the onset of super (1982, 1997, and 2015) and moderate El Niño events. The results revealed that extreme WWBs during the onset of the super El Niño group were attributed to low-frequency westerly (≥90 days, LFW), medium-frequency westerly (20–90 days, MFW, or intraseasonal) and high-frequency westerly (≤10 days, HFW) components, accounting for approximately 51%, 33% and 16%, respectively. Thus, the extreme WWBs during the onset of super El Niños were primarily contributed by LFWs and MFWs. By contrast, the WWBs during the onset of moderate El Niños were determined primarily by MFWs (38%) and HFWs (35%), whereas the LFW contribution is relatively small (27%). A further analysis indicated that LFWs during the onset of the super El Niños were primarily a response to a positive SST anomaly in the tropical to eastern North Pacific resembling the Pacific Meridional Mode (PMM), which had persisted during the preceding 9–12 months in the extratropical eastern North Pacific. A significant lagged correlation between the tropical and extratropical North Pacific SST was identified, and their correlation has become stronger since the late 1980s. MFWs during the onset of the super El Niños were primarily associated with the Madden-Julian Oscillation.

scholarly journals Observations and Mechanisms of a Simple Stochastic Dynamical Model Capturing El Niño Diversity

2017 ◽  
Vol 31 (1) ◽  
pp. 449-471 ◽  
Author(s):  
Nan Chen ◽  
Andrew J. Majda ◽  
Sulian Thual
Keyword(s):  
El Niño ◽  
El Nino ◽  
Heat Content ◽  
Trade Wind ◽  
Formation Mechanisms ◽  
Modeling Framework ◽  
Easterly Wind ◽  
Cp El Niño ◽  
Nonlinear Advection ◽  
Wind Bursts

Abstract El Niño–Southern Oscillation (ENSO) has significant impact on global climate and relevance for seasonal forecasts. Recently, a simple modeling framework was developed that captures the ENSO diversity, where state-dependent stochastic wind bursts and nonlinear advection of sea surface temperature are coupled to a simple ocean–atmosphere model that is otherwise deterministic, linear, and stable. In this article, the coupled model is compared with observations using reanalysis data over the last 34 yr, where the observed non-Gaussian statistics and the overall mechanisms of ENSO are both captured by the model. Then the formation mechanisms of both the central Pacific (CP) and the traditional El Niño in the model are systematically studied. First, ocean Rossby waves induced by easterly trade wind anomalies facilitate the heat content buildup. Then the reflected ocean Kelvin waves and the nonlinear advection lead to positive SST anomalies in the CP region and create a CP El Niño. Second, two formation mechanisms are revealed for the traditional El Niño, including the super (extreme) El Niño. The first mechanism indicates a preferred wind structure with easterly wind bursts (EWBs) leading westerly wind bursts (WWBs), where the EWBs build up heat content and then the WWBs trigger the El Niño. The second mechanism links the two types of El Niño, where a CP El Niño favors a heat content buildup and the advent of a traditional El Niño. This article also highlights the mechanisms of La Niña formation and El Niño termination.

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

2020 ◽  
Author(s):  
Tomoki Iwakiri ◽  
Masahiro Watanabe
Keyword(s):  
El Niño ◽  
El Nino ◽  
Heat Content ◽  
La Niña ◽  
Ekman Transport ◽  
Atmospheric Conditions ◽  
Late 20Th Century ◽  
Easterly Wind ◽  
La Nina ◽  
Extreme El Niño

Abstract El Niño/La Niña, characterized by anomalous sea surface temperature warming/cooling in the central-eastern equatorial Pacific, is a dominant interannual variability with irregularity, impacting worldwide weather and socioeconomics. The observed records show that La Niña often persists for more than two years, called “multi-year La Niña” which tends to accompany extreme El Niño in the preceding year; however, the physical linkage between them remains unclear. Here we show using reanalysis data that an extreme El Niño excites atmospheric conditions that favor the generation of the multi-year La Niña in subsequent years. Easterly wind anomalies along the northern off-equator in the Pacific during the decay phase of an extreme El Niño are crucial. 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) models show that the occurrence frequencies of multi-year La Niña and extreme El Niño are highly correlated, supporting the abovementioned mechanism. Our results provide physical evidence that the increasing frequency of multi-year La Niña is explained by the increasing El Niño amplitude since the late 20th century.

scholarly journals Exceptionally strong easterly wind burst stalling El Niño of 2014

2016 ◽  
Vol 113 (8) ◽  
pp. 2005-2010 ◽  
Author(s):  
Shineng Hu ◽  
Alexey V. Fedorov
Keyword(s):  
El Niño ◽  
Climate Models ◽  
Climate Model ◽  
Extreme Event ◽  
El Nino ◽  
Tropical Pacific ◽  
Bjerknes Feedback ◽  
Easterly Wind ◽  
Wind Bursts ◽  
The Tropical Pacific

Intraseasonal wind bursts in the tropical Pacific are believed to affect the evolution and diversity of El Niño events. In particular, the occurrence of two strong westerly wind bursts (WWBs) in early 2014 apparently pushed the ocean–atmosphere system toward a moderate to strong El Niño—potentially an extreme event according to some climate models. However, the event’s progression quickly stalled, and the warming remained very weak throughout the year. Here, we find that the occurrence of an unusually strong basin-wide easterly wind burst (EWB) in June was a key factor that impeded the El Niño development. It was shortly after this EWB that all major Niño indices fell rapidly to near-normal values; a modest growth resumed only later in the year. The easterly burst and the weakness of subsequent WWBs resulted in the persistence of two separate warming centers in the central and eastern equatorial Pacific, suppressing the positive Bjerknes feedback critical for El Niño. Experiments with a climate model with superimposed wind bursts support these conclusions, pointing to inherent limits in El Niño predictability. Furthermore, we show that the spatial structure of the easterly burst matches that of the observed decadal trend in wind stress in the tropical Pacific, suggesting potential links between intraseasonal wind bursts and decadal climate variations.

scholarly journals Seasonally-dependent impact of easterly wind bursts on the development of El Niño events

2019 ◽  
Vol 53 (3-4) ◽  
pp. 1527-1546 ◽  
Author(s):  
Hanjie Fan ◽  
Bohua Huang ◽  
Song Yang ◽  
Zhenning Li ◽  
Kaiqiang Deng
Keyword(s):  
El Niño ◽  
El Nino ◽  
Easterly Wind ◽  
El Niño Events ◽  
Wind Bursts ◽  
El Nino Events

scholarly journals Effects of Excessive Equatorial Cold Tongue Bias on the Projections of Tropical Pacific Climate Change. Part II: The Extreme El Niño Frequency in CMIP5 Multi-Model Ensemble

Atmosphere ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 851
Author(s):  
Gen Li ◽  
Zhiyuan Zhang ◽  
Bo Lu
Keyword(s):  
El Niño ◽  
Climate Models ◽  
El Nino ◽  
Equatorial Pacific ◽  
Western Pacific ◽  
Warming Pattern ◽  
El Niño Events ◽  
Rcp 8.5 ◽  
Extreme El Niño ◽  
El Nino Events

Under increased greenhouse gas (GHG) forcing, climate models tend to project a warmer sea surface temperature in the eastern equatorial Pacific than in the western equatorial Pacific. This El Niño-like warming pattern may induce an increase in the projected occurrence frequency of extreme El Niño events. The current models, however, commonly suffer from an excessive westward extension of the equatorial Pacific cold tongue accompanied by insufficient equatorial western Pacific precipitation. By comparing the Representative Concentration Pathway (RCP) 8.5 experiments with the historical simulations based on the Coupled Model Intercomparison Project phase 5 (CMIP5), a “present–future” relationship among climate models was identified: models with insufficient equatorial western Pacific precipitation error would have a weaker mean El Niño-like warming pattern as well as a lower increase in the frequency of extreme El Niño events under increased GHG forcing. Using this “present–future” relationship and the observed precipitation in the equatorial western Pacific, this study calibrated the climate projections in the tropical Pacific. The corrected projections showed a stronger El Niño-like pattern of mean changes in the future, consistent with our previous study. In particular, the projected increased occurrence of extreme El Niño events under RCP 8.5 forcing are underestimated by 30–35% in the CMIP5 multi-model ensemble before the corrections. This implies an increased risk of the El Niño-related weather and climate disasters in the future.

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.

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