Quantifying the Role of Oceanic Feedbacks on ENSO Asymmetry

Guan, Cong; McPhaden, Michael J.; Wang, Fan; Hu, Shijian

doi:10.1029/2018gl081332

Cited by 30 publications

(33 citation statements)

References 63 publications

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“…As a result, delayed negative oceanic feedback to the weak wind during La Niña is weak, making phase transition difficult. In addition, the asymmetrical responses of subsurface ocean temperature to the thermocline, as well as ocean waves to wind forcing according to the mean thermocline depth and the wind pattern, are also emphasised as primary causes of El Niño and La Niña persistency (DiNezio and Deser, 2014; Im et al, 2015; An and Kim, 2017; Guan et al, 2019). Weaker thermo‐dynamical damping also plays an important role in the long persistence of a La Niña event (Chen et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Mid‐latitude leading double‐dip La Niña

Park

Kug

et al. 2020

Intl Journal of Climatology

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Understanding the evolution asymmetry between El Niño and La Niña events is challenging. Unlike El Niño, most La Niña events are characterised by a double-dip cooling (a.k.a. multi-year La Niña). Herein, we examined how single-and multi-year La Niña events differ by analysing observational and climate-model data sets. Single-year La Niña events tend to develop narrowly within the tropics from a central Pacific-type El Niño (Niño-4 > Niño-3), whereas multi-year La Niña events tend to originate from an eastern Pacifictype El Niño (Niño-3 > Niño-4) and are well-connected to mid-latitudes through the Pacific meridional mode, which leads to a meridionally wider response of the off-equatorial low-level atmospheric anti-cyclonic circulation. As the anti-cyclonic circulation controls the amount of equatorial upper-ocean heat recharge through Sverdrup transport, for single-year La Niña, efficient ocean recharging due to a narrower anti-cyclonic circulation causes a fast transition to an El Niño or a fast termination of a La Niña. In contrast, for multiyear La Niña, a weaker recharging causes surface cooling to persist, leading to another La Niña in the following year.

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Section: Introductionmentioning

confidence: 99%

Mid‐latitude leading double‐dip La Niña

Park

Kug

et al. 2020

Intl Journal of Climatology

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“…This process is however lacked for the La Niña (Okumura & Deser, 2010), allowing the occurrence of multiyear events. The asymmetric evolutions between El Niño and La Niña are consistent with the recharge/discharge regime that is linked to sea level-related ocean dynamics (Guan et al, 2019;Hu et al, 2016). Also interesting is to look at whether the asymmetric SLAs can in turn contribute to the ENSO asymmetry through advection or other processes (e.g., An & Jin, 2004;Jin et al, 2003;Su et al, 2010).…”

Section: 1029/2020jc016616mentioning

confidence: 77%

“…On the other hand, SLAs are dynamically associated with the thermocline displacements and the upper ocean geostrophic current anomalies. The asymmetry in SLAs may further lead to asymmetries in upwelling/downwelling and ocean current advection for SST and thereby contribute to the ENSO asymmetry (e.g., An & Jin, 2004; Choi et al, 2013; Dinezio & Deser, 2014; Guan et al, 2019; Hu et al, 2016; Jin et al, 2003; Kang & Kug, 2002; Su et al, 2010; Wen et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

“…Statistical analysis of previous studies (Burgers & Stephenson, 1999; Niedzielski, 2010; Niedzielski & Kosek, 2010) suggested that SLAs over the tropical Pacific, resembling sea surface temperature (SST) anomalies, do not strictly conform to the normal distribution. As shown in Figure 1d, the prevailing negative skewness values in the WTP are probably linked to the predominance of El Niño over La Niña in their SLA signatures (Niedzielski & Kosek, 2010), which may be related with not only the ENSO's asymmetry but also the nonlinearity in ocean response to ENSO (An & Kim, 2017; Guan et al, 2019; Im et al, 2015; Niedzielski & Kosek, 2010; Świerczyńska et al, 2014; Wen et al, 2014). El Niño and La Niña, modulated by nonlinear processes of the tropical Pacific climate, are not perfect mirrors of each other and show asymmetries in amplitude, duration time, and occurrence frequency (e.g., An & Choi, 2009; An & Jin, 2004; Burgers & Stephenson, 1999; Gergis & Fowler, 2009; Guan et al, 2019; Hu et al, 2016; Jin et al, 2003; Ohba & Ueda, 2007; Okumura & Deser, 2010; Su et al, 2010; Yu et al, 1997).…”

Section: Introductionmentioning

confidence: 99%

“…The CP type has been occurring more frequently in recent decades (e.g., Ashok et al, 2007; Kao & Yu, 2009; Kug et al, 2009; Lee & McPhaden, 2010; McPhaden et al, 2011), which has been attributed to anthropogenic global warming (Yeh et al, 2009) and forcing by the Atlantic multidecadal oscillation (Yu et al, 2015). It has been suggested that the ocean dynamics of the EP type are amenable to theoretical interpretations of the delayed and recharged oscillators, but those of the CP type are not (e.g., Guan et al, 2019; Kug et al, 2009; Ren & Jin, 2013).…”

Section: Introductionmentioning

confidence: 99%

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Asymmetry of Interannual Sea Level Variability in the Western Tropical Pacific: Responses to El Niño and La Niña

Ren

Zheng

et al. 2020

JGR Oceans

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The western tropical Pacific (WTP) exhibits pronounced large-scale sea level anomalies (SLAs) during El Niño-Southern Oscillation (ENSO) events with amplitudes of~0.1 m, exerting potential threats to many low-lying islands. It is found that the sea level falling in El Niño condition is evidently stronger than the rising in La Niña condition. This SLA asymmetry in the WTP associated with ENSO is investigated in this study, and the underlying dynamic processes are explored. Such asymmetry is most prominent at around 160°E with the SLA response to El Niño being three times stronger than to La Niña, but it is much inconspicuous near the western boundary. Sensitivity experiments of a simplified ocean model suggest that the different structures of surface wind anomalies between El Niño and La Niña conditions are critical in generating asymmetric SLA responses of the WTP. The El Niño's westerly wind anomaly patch locates more to the east than the La Niña's easterly wind patch during the mature stage, and its upwelling effects are accumulated over a wider longitude range and cause stronger negative SLAs in the WTP. Near the western boundary, however, upwelling effects are attenuated by easterly wind anomalies during the mature stage of El Niño. Further analysis reveals that eastern Pacific-type El Niño events are more favorable for generating asymmetric SLAs in the WTP than the central Pacific-type events. Plain Language Summary El Niño-Southern Oscillation (ENSO) is the most important climate variability phenomenon in the tropical Pacific and causes strong interannual sea level anomalies (SLAs) in the western tropical Pacific (WTP). The El Niño's sea level falling is evidently stronger than the La Niña's sea level rising. This difference is most prominent near 160°E with stronger El Niño's sea level falling but becomes much less evident near the western boundary of the Pacific Basin. The different surface wind anomaly structures between El Niño and La Niña are the primary cause. El Niño's westerly wind anomaly center locates more east than La Niña's easterly wind anomaly center in their mature phase, leading to stronger sea level falling in the WTP through westerly wind anomalies over the wide longitude range. The sea level falling is weakened by easterly wind anomalies generated near the western boundary. By contrast, effect of La Niña's easterly wind anomaly strengthens monotonically from east to west, and the produced sea level rising signatures are mainly confined to the WTP. The wind forcing structure of eastern Pacific-type El Niño is more favorable for generating asymmetric SLAs in the WTP than central Pacific-type events.

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Evidence of nonlinear Walker circulation feedbacks on extreme El Niño Pacific diversity: Observations and CMIP5 models

Sulca

2021

Intl Journal of Climatology

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The Walker circulation (WC) is essential for the formation and diversity of El Niño events. However, the nonlinear WC feedback during extreme Central and Eastern El Niño episodes (C and E episodes, respectively) has received little attention. This study used observational datasets and the Atmospheric Model Intercomparison Project (AMIP) and historical simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5). Eight out of 21 historical models that simulate the El Niño‐Southern Oscillation (ENSO) nonlinearity also simulate the nonlinear Bjerknes feedback in C and E episodes. The opposite does not necessarily occur. However, the underestimation of E might limit the empirical determination. Moreover, few historical models simulate the shallow conditional instability of the second kind (CISK) mechanism. Positive C episodes feature an eastward shift in the ascending branch of the Pacific Walker cell (PWC), while shallow convection prevails over the far‐eastern Pacific (FEP). Positive E events feature two anomalous ascending branches located over the central‐western Pacific (170°W) and FEP (80°W). Positive anomalies in sea surface temperature over the FEP induce the second ascending branch. The positive stratification anomaly in the central Pacific Ocean, which is associated with overestimated Ekman feedback, limits the eastward displacement of the first ascending branch of the PWC. The net surface heat flux determines the duration of growth of the two ascending branches of the PWC during C and E events. Because of their coarse resolution, the historical models underestimate the positive stratification anomaly in the FEP, causing the quick demise of the second ascending branch.

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Quantifying the Role of Oceanic Feedbacks on ENSO Asymmetry

Cited by 30 publications

References 63 publications

Mid‐latitude leading double‐dip La Niña

Mid‐latitude leading double‐dip La Niña

Asymmetry of Interannual Sea Level Variability in the Western Tropical Pacific: Responses to El Niño and La Niña

Evidence of nonlinear Walker circulation feedbacks on extreme El Niño Pacific diversity: Observations and CMIP5 models

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