A Proposed Mechanism for the Asymmetric Duration of El Niño and La Niña

Okumura, Yoshiyuki; Ohba, Masamichi; Deser, Clara; Ueda, Hiroaki

doi:10.1175/2011jcli3999.1

Cited by 119 publications

(85 citation statements)

References 30 publications

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“…A large fraction (35%-50%) of La Niña events last two years or longer (Okumura and Deser 2010) in contrast to El Niño events, which rarely last longer than one year. The multiyear persistence of La Niña exacerbates its global climate impacts, especially in regions prone to drought.…”

Section: Introductionmentioning

confidence: 94%

“…Note that 50% of observed La Niña events lasted 2 yr or longer during the 1950-2010 period (Okumura and Deser 2010). This value is not inconsistent with the CCSM4 simulation because the frequency of occurrence of simulated 2-yr LN exhibits remarkable century-to-century variations.…”

Section: Two-year La Niña Eventsmentioning

confidence: 99%

“…In both the simulated and the reanalysis data, El Niño events exhibit larger zonal wind stress anomalies than La Niña events for SST anomalies of the same magnitude. This wind-SST nonlinearity has been linked to the effect of background SST on the convective response of the tropical atmosphere (Hoerling et al 1997) and invoked to explain asymmetries between the amplitude of El Niño and La Niña (Kang and Kug 2002) and also in their duration (Okumura et al 2011;Choi et al 2013;Dommenget et al 2013).…”

Section: Delayed Thermocline Feedback Nonlinearity a Nonlinear Procementioning

confidence: 99%

“…The multiyear persistence of La Niña exacerbates its global climate impacts, especially in regions prone to drought. Several observational studies have documented the asymmetry in the duration of the two phases of El Niño-Southern Oscillation (ENSO) (e.g., Kessler 2002;Larkin and Harrison 2002;McPhaden and Zhang 2009;Ohba and Ueda 2009;Wu et al 2010;Okumura and Deser 2010;Ohba et al 2010;Hu et al 2013). For instance, during the 1980-2008 period, sea surface temperature (SST) observations show that La Niña tends to persist into a second year, reintensifying during the following boreal winter (McPhaden and Zhang 2009).…”

Section: Introductionmentioning

confidence: 99%

“…Ohba and Ueda (2009) and Okumura et al (2011) argue that it is caused by wind anomalies that are shifted westward and of weaker magnitude during La Niña events. This asymmetric wind response occurs because of differences in the location of precipitation anomalies over the western Pacific between El Niño and La Niña, resulting in wind anomalies of different magnitudes (Ohba and Ueda 2009;Frauen and Dommenget 2010;Okumura et al 2011). Choi et al (2013) also showed that this nonlinearity plays a role in the asymmetric duration of ENSO events, however, by influencing the termination of La Niña through the delayed adjustment of the thermocline to wind anomalies.…”

Section: Introductionmentioning

confidence: 99%

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Nonlinear Controls on the Persistence of La Niña*

2014

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A large fraction (35%-50%) of observed La Niña events last two years or longer, in contrast to the great majority of El Niño events, which last one year. Here, the authors explore the nonlinear processes responsible for the multiyear persistence of La Niña in the Community Climate System Model, version 4 (CCSM4), a coupled climate model that simulates the asymmetric duration of La Niña and El Niño events realistically. The authors develop a nonlinear delayed-oscillator (NDO) model of the El Niño-Southern Oscillation (ENSO) to explore the mechanisms governing the duration of La Niña. The NDO includes nonlinear and seasonally dependent feedbacks derived from the CCSM4 heat budget, which allow it to simulate key ENSO features in quantitative agreement with CCSM4.Sensitivity experiments with the NDO show that the nonlinearity in the delayed thermocline feedback is the sole process controlling the duration of La Niña events. The authors' results show that, as La Niña events become stronger, the delayed thermocline response does not increase proportionally. This nonlinearity arises from two processes: 1) the response of winds to sea surface temperature anomalies and 2) the ability of thermocline depth anomalies to influence temperatures at the base of the mixed layer. Thus, strong La Niña events require that the thermocline remains deeper for longer than 1 yr for sea surface temperatures to return to neutral. Ocean reanalysis data show evidence for this thermocline nonlinearity, suggesting that this process could be at work in nature.

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Section: Introductionmentioning

confidence: 94%

Section: Two-year La Niña Eventsmentioning

confidence: 99%

Section: Delayed Thermocline Feedback Nonlinearity a Nonlinear Procementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nonlinear Controls on the Persistence of La Niña*

2014

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Interbasin effects of the Indian Ocean on Pacific decadal climate change

Mochizuki

Kimoto

Chikamoto

et al. 2016

Geophysical Research Letters

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We demonstrate the significant impact of the Indian Ocean on the Pacific climate on decadal timescales by comparing two sets of data assimilation experiments (pacemaker experiments) conducted over recent decades. For the Indian Ocean of an atmosphere‐ocean coupled global climate model, we assimilate ocean temperature and salinity anomalies defined as deviations from climatology or as anomalies with the area‐averaged changes for the Indian Ocean subtracted. When decadal sea surface temperature (SST) trends are observed to be strong over the Indian Ocean, the equatorial thermocline uniformly deepens, and the model simulates the eastward tendencies of surface wind aloft. Surface winds strongly converge around the maritime continent, and the associated strengthening of the Walker circulation suppresses an increasing trend in the equatorial Pacific SST through ocean thermocline shoaling, similar to common changes associated with seasonal Indian Ocean warming.

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Role of nonlinear ocean dynamic response to wind on the asymmetrical transition of El Niño and La Niña

Kim

2017

Geophysical Research Letters

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To understand why El Niño is frequently followed by La Niña while the opposite occurs rarely, we analyze the inherent asymmetry in a delayed negative feedback loop in the framework of delayed oscillator theory using observational data. The asymmetrical response of the ocean wave to wind is much larger than that of the wind intensity to sea surface temperature (SST) and that of the subsurface temperature to thermocline. Strong oceanic response during El Niño compared to La Niña is presumably due to the relatively shallow mean thermocline over the western Pacific, which efficiently traps the atmospheric momentum in the shallow upper ocean, and the asymmetrical wind pattern response to SST. A modified delayed oscillator model experiment verifies that the asymmetrical ocean wave response to wind is more important in the asymmetrical transition of El Niño and La Niña than asymmetrical wind intensity response to SST and asymmetrical subsurface temperature response to thermocline.

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A Proposed Mechanism for the Asymmetric Duration of El Niño and La Niña

Cited by 119 publications

References 30 publications

Nonlinear Controls on the Persistence of La Niña*

Nonlinear Controls on the Persistence of La Niña*

Interbasin effects of the Indian Ocean on Pacific decadal climate change

Role of nonlinear ocean dynamic response to wind on the asymmetrical transition of El Niño and La Niña

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