Analysis of the non-linearity in the pattern and time evolution of El Niño southern oscillation

Dommenget, Dietmar; Bayr, Tobias; Frauen, Claudia

doi:10.1007/s00382-012-1475-0

Cited by 213 publications

(240 citation statements)

References 37 publications

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“…7a, b indicate that the observed SLA associated with El Niño are a little stronger and shifted about 15°t o the east compared to those of La Niña. The asymmetric SLA pattern generated by PEODAS for the two ENSO states reflects similar findings from Kang and Kug (2002) and Dommenget et al (2012).…”

Section: Mature Enso Eventssupporting

confidence: 67%

Seasonal prediction of global sea level anomalies using an ocean–atmosphere dynamical model

et al. 2014

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Advanced warning of extreme sea level events is an invaluable tool for coastal communities, allowing the implementation of management policies and strategies to minimise loss of life and infrastructure damage. This study is an initial attempt to apply a dynamical coupled oceanatmosphere model to the prediction of seasonal sea level anomalies (SLA) globally for up to 7 months in advance. We assess the ability of the Australian Bureau of Meteorology's operational seasonal dynamical forecast system, the Predictive Ocean Atmosphere Model for Australia (POAMA), to predict seasonal SLA, using gridded satellite altimeter observation-based analyses over the period 1993-2010 and model reanalysis over 1981-2010. Hindcasts from POAMA are based on a 33-member ensemble of seasonal forecasts that are initialised once per month for the period 1981-2010. Our results show POAMA demonstrates high skill in the equatorial Pacific basin and consistently exhibits more skill globally than a forecast based on persistence. Model predictability estimates indicate there is scope for improvement in the higher latitudes and in the Atlantic and Southern Oceans. Most characteristics of the asymmetric SLA fields generated by ElNino/La Nina events are well represented by POAMA, although the forecast amplitude weakens with increasing lead-time.

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Section: Mature Enso Eventssupporting

confidence: 67%

Seasonal prediction of global sea level anomalies using an ocean–atmosphere dynamical model

et al. 2014

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“…This nonlinearity is due to the dependence of the subsurface temperature gradient DT 0 sub on Z 0 tc , which leads to a less effective delayed thermocline-driven termination of La Niña events. Nonlinearities in other processes, such as the response of winds to SST anomalies, could also increase the duration of La Niña as proposed by previous studies (Choi et al 2013;Dommenget et al 2013); however, our analysis shows that the DT 0 sub -Z 0 tc nonlinearity is required to explain the large fraction (35%) of 2-yr LN events simulated by CCSM4. Furthermore, the thermocline nonlinearity has a direct effect on the spectral properties of ENSO resulting in a broader and longer period.…”

Section: Discussionsupporting

confidence: 52%

“…Similarly, 2-yr La Niña events are not as common as in CCSM4 in the model of Dommenget et al (2013). This can be seen in their Fig.…”

Section: Discussionmentioning

confidence: 77%

“…persistent La Niña events (Okumura et al 2011;Choi et al 2013;Dommenget et al 2013); however, they also conclude that this nonlinearity alone does not produce as many persistent La Niña events as observed (Choi et al 2013). Similarly, 2-yr La Niña events are not as common as in CCSM4 in the model of Dommenget et al (2013).…”

Section: Discussionmentioning

confidence: 88%

“…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%

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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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Extreme swings of the South Pacific Convergence Zone and the different types of El Niño events

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Santoso

Cai

et al. 2014

Geophysical Research Letters

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There have been three extreme equatorward swings of the South Pacific Convergence Zone (SPCZ) during the satellite era. These zonal SPCZ (zSPCZ) events coincided with an El Niño of different magnitude and spatial pattern, in which strong anomalous warming reduced the off-equatorial-to-equatorial meridional sea surface temperature (SST) gradient near the dateline, enabling convection to shift equatorward. It is not known, given the short observational record, how and whether different types of El Niño are associated with zSPCZ events. Using perturbed physics ensembles experiments in which SST biases are reduced, we find that zSPCZ events are concurrent with notable eastern Pacific (EP) warming. Central Pacific warming alone is rarely able to produce a swing, even as the climate warms under a CO 2 increase scenario. Only El Niño events with strong EP warming can shift the convective zone. Such co-occurring events are found to increase in frequency under greenhouse warming.

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Analysis of the non-linearity in the pattern and time evolution of El Niño southern oscillation

Cited by 213 publications

References 37 publications

Seasonal prediction of global sea level anomalies using an ocean–atmosphere dynamical model

Seasonal prediction of global sea level anomalies using an ocean–atmosphere dynamical model

Nonlinear Controls on the Persistence of La Niña*

Extreme swings of the South Pacific Convergence Zone and the different types of El Niño events

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