El Niño, La Niña, and the Nonlinearity of Their Teleconnections

Hoerling, Martin P.; Kumar, Arun; Zhong, Min

doi:10.1175/1520-0442(1997)010<1769:enolna>2.0.co;2

Cited by 719 publications

(642 citation statements)

References 27 publications

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“…Hoerling et al (1997) found a 2°C increase (in December-February) between the Great Lakes and Hudson Bay for nine EN events between 1958 and 1995. This anomalous warm air leads then to less cyclogenesis downstream, due to the reduced continent-sea thermal contrast, over the northwest North Atlantic, and then a possible filling of the Iceland low and an overall reduction of the North Atlantic storm track (May and Bengtsson, 1998;May, 1999).…”

Section: Discussionmentioning

confidence: 99%

“…In JFM, the anomalously positive (negative) frequency of GA and WBL (EA and ZO) during EN events could be explained by the following mechanism, involving a dynamical link between the intensity of the Aleutian and Icelandic lows (Honda et al, 2001): the Aleutian low is anomalously intensified during EN winters (Hoerling et al 1997;Robertson and Ghil, 1999), leading to warm temperature anomalies across North America, mainly western and eastern Canada where above-normal temperatures occur during the December-May period synchronous with an EN event (Halpert and Ropelewski, 1992). Hoerling et al (1997) found a 2°C increase (in December-February) between the Great Lakes and Hudson Bay for nine EN events between 1958 and 1995.…”

Section: Discussionmentioning

confidence: 99%

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The impact of El Niño–southern oscillation upon weather regimes over Europe and the North Atlantic during boreal winter

Moron

Plaut

2003

Intl Journal of Climatology

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The influence of the warm and cold sea-surface temperatures in the eastern and central equatorial Pacific associated with El Niño-southern oscillation (ENSO) on the probability of occurrence of weather regimes (WRs) over the North Atlantic sector is investigated for the period November-March. Five WRs are identified from daily sea-level pressure anomalies (SLPAs) during 119 winters over this sector by applying cluster analysis: the positive North Atlantic oscillation (NAO; called ZO for zonal) and negative NAO (called WBL for west blocking) patterns; GA (for Greenland anticyclone), with a positive SLPA shifted north of 60°N; EA (for European anticyclone) with a positive SLPA over Europe but enhanced north-south SLPA gradient over the western and central North Atlantic; and AR (for Atlantic Ridge) with a positive (negative) SLPA over the central North Atlantic (northern and central Europe).El Niño winters are associated with a significant increase (decrease) in the prevalence of ZO (WBL) in November-December and a significant increase (decrease) in the prevalence of GA and WBL (EA and ZO)

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

The impact of El Niño–southern oscillation upon weather regimes over Europe and the North Atlantic during boreal winter

Moron

Plaut

2003

Intl Journal of Climatology

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“…This nonlinearity appears to be related to the response of zonal winds (the driver of u 0 and w 0 ), which is stronger for positive T 0 than for negative T 0 (not shown). This wind-SST nonlinearity has been linked to the effect of background SST on the convective response, which leads to a much larger convective response for warm anomalies (Hoerling et al 1997;Kang and Kug 2002;Frauen and Dommenget 2010). The strength of the associated positive feedback (given by the slope of the scatterplot) appears to be modulated by the seasonal cycle, with the largest values in boreal summer (June-August) ( Fig.…”

Section: Nonlinearities In the Enso Heat Budgetmentioning

confidence: 98%

“…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%

Nonlinear Controls on the Persistence of La Niña*

DiNezio

Deser

2014

Journal of Climate

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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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“…For this reason, we choose the N3.4 index from the NCEP/CPC. In addition, these indices have been computed using sea surface temperature (SST) anomalies (e.g., Butler and Polvani 2011;Garfinkel et al 2012) or their standardized values (e.g., Hoerling et al 1997;Mitchell et al 2011). Finally, different thresholds have been applied to select the events.…”

Section: A Event Detectionmentioning

confidence: 99%

The Stratospheric Pathway of La Niña

2016

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A Northern Hemisphere (NH) polar stratospheric pathway for La Nina events is established during win tertime based on reanalysis data for the 1958-2012 period. A robust polar stratospheric response is observed in the NH during strong La Nina events, characterized by a significantly stronger and cooler polar vortex. Significant wind anomalies reach the surface, and a robust impact on the North Atlantic-European (NAE) region is observed. A dynamical analysis reveals that the stronger polar stratospheric winds during La Nina winters are due to reduced upward planetary wave activity into the stratosphere. This finding is the result of destructive interference between the climatological and the anomalous La Nina tropospheric stationary eddies over the Pacific-North American region.In addition, the lack of a robust stratospheric signature during La Nina winters reported in previous studies is investigated. It is found that this is related to the lower threshold used to detect the events, which signature is consequently more prone to be obscured by the influence of other sources of variability. In particular, the occurrence of stratospheric sudden warmings (SSWs), partly linked to the phase of the quasi-biennial oscil lation, modulates the observed stratospheric signal. In the case of La Nina winters defined by a lower threshold, a robust stratospheric cooling is found only in the absence of SSWs. Therefore, these results highlight the importance of using a relatively restrictive threshold to define La Nina events in order to obtain a robust surface response in the NAE region through the stratosphere.

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El Niño, La Niña, and the Nonlinearity of Their Teleconnections

Cited by 719 publications

References 27 publications

The impact of El Niño–southern oscillation upon weather regimes over Europe and the North Atlantic during boreal winter

The impact of El Niño–southern oscillation upon weather regimes over Europe and the North Atlantic during boreal winter

Nonlinear Controls on the Persistence of La Niña*

The Stratospheric Pathway of La Niña

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