On the dynamical mechanisms explaining the western Pacific subsurface temperature buildup leading to ENSO events

Ballester, Joan; Bordoni, Simona; Petrova, Desislava; Rodó, Xavier

doi:10.1002/2015gl063701

Cited by 14 publications

(29 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The equatorial easterly wind anomalies (or, more precisely, the off-equatorial wind stress curl) observed before and after the beginning of the simulations are associated with the positive change rate in subsurface meridional convergence1011. This tendency towards equatorward mass convergence is associated with upwelling of subsurface cold waters that favors the persistence of cold SST and easterly wind anomalies in the central Pacific, which in turn deepen the thermocline and accumulate subsurface warm waters in the western Pacific26. A weak LN event therefore develops at the end of year −1, which re-activates the generation of the subsurface heat buildup in the western Pacific.…”

mentioning

confidence: 92%

“…This paradigm, which has been thoroughly validated in the literature2223, describes a recharge (discharge) phase of Warm Water Volume (WWV) along the equator that leads EN (LN) events by about 2 to 3 seasons2124. This stage is in turn preceded by the tilting mode22526, which is characterized by an anomalous zonal gradient of the depth of the thermocline and is significantly associated with ENSO at long-lead times (e.g. the correlation between ENSO and WWV anomalies to the west of 155W is around 0.57 at lag 15 months, see ref.…”

mentioning

confidence: 95%

“…Instead, in the simulations in which the initial heat content has been completely or largely suppressed (i.e. −100% and −80%), the equatorward mass convergence is associated with the upwelling of subsurface cold waters that favors the persistence of cold SST and easterly wind anomalies in the central Pacific, which in turn deepen the thermocline and generate a new heat buildup in the western Pacific2627. We must however note that, in a more general framework, the initial THC could increase at a different rate or even decrease if wind stress anomalies were also prescribed or a different time frame was chosen as initial conditions for the experiments.…”

mentioning

confidence: 98%

“…beginning of the simulations). Reference 26 showed that meridional and eastward heat advection due to equatorward subsurface mass convergence and transport along the equatorial undercurrent contribute to this long-leading subsurface warming at 170E-150W, while surface horizontal convergence and downwelling motion have a leading role in subsurface warming in the warm pool. Westerly wind anomalies appear at the beginning of the following year, when the warm waters start to propagate to the eastern Pacific along the equatorial thermocline as downwelling Kelvin waves.…”

mentioning

confidence: 99%

See 3 more Smart Citations

Sensitivity of El Niño intensity and timing to preceding subsurface heat magnitude

Ballester

Petrova

Bordoni

et al. 2016

Sci Rep

Self Cite

View full text Add to dashboard Cite

Despite extensive ongoing efforts on improving the long-term prediction of El Niño-Southern Oscillation, the predictability in state-of-the-art operational schemes remains limited by factors such as the spring barrier and the influence of atmospheric winds. Recent research suggests that the 2014/15 El Niño (EN) event was stalled as a result of an unusually strong basin-wide easterly wind burst in June, which led to the discharge of a large fraction of the subsurface ocean heat. Here we use observational records and numerical experiments to explore the sensitivity of EN to the magnitude of the heat buildup occurring in the ocean subsurface 21 months in advance. Our simulations suggest that a large increase in heat content during this phase can lead to basin-wide uniform warm conditions in the equatorial Pacific the winter before the occurrence of a very strong EN event. In our model configuration, the system compensates any initial decrease in heat content and naturally evolves towards a new recharge, resulting in a delay of up to one year in the occurrence of an EN event. Both scenarios substantiate the non-linear dependency between the intensity of the subsurface heat buildup and the magnitude and timing of subsequent EN episodes.

show abstract

mentioning

confidence: 92%

mentioning

confidence: 95%

mentioning

confidence: 98%

mentioning

confidence: 99%

See 2 more Smart Citations

Sensitivity of El Niño intensity and timing to preceding subsurface heat magnitude

Ballester

Petrova

Bordoni

et al. 2016

Sci Rep

Self Cite

View full text Add to dashboard Cite

show abstract

“…EN (LN) is always preceded by a meridional recharge (discharge) of basin-wide tropical ocean heat content about two to three seasons in advance, which deepens (shoals) the whole equatorial thermocline and warms (cools) the ocean subsurface at about 100 to 150 m depth [Meinen and McPhaden, 2000;Ramesh and Murtugudde, 2013]. This phase is in turn typically led by the tilting mode, a maximum (minimum) in the slope of the equatorial thermocline explained by the strengthening (weakening) of the equatorial trade winds and the subsequent anomalous downwelling (upwelling) of surface warm (subsurface cold) waters in the western Pacific warm pool [Wyrtki, 1985;Ballester et al, 2015].…”

Section: Introductionmentioning

confidence: 99%

Timing of subsurface heat magnitude for the growth of El Niño events

Ballester

Petrova

Bordoni

et al. 2017

Geophysical Research Letters

Self Cite

View full text Add to dashboard Cite

The subsurface heat buildup in the western tropical Pacific and the recharge phase in equatorial heat content are intrinsic elements of El Niño–Southern Oscillation, leading to changes in zonal wind stress, sea surface temperature, and thermocline tilt that characterize the growing and mature phases of El Niño (EN) events. Here we use numerical simulations to study the impact on subsequent EN episodes of a sudden increase or decrease in ocean heat content during the recharge phase and compare results with previous studies in which this perturbation is prescribed earlier during the tilting mode. We found that while not substantially affected by the phase at which a sudden rise in heat content is prescribed, the timing and magnitude of the events are very sensitive to the phase at which a major decrease is imposed. The different response to the phase of increases and decreases substantiates the importance of nonlinear subsurface ocean dynamics to the onset and growth of EN episodes and provides insight into the irreversibility of the events at different stages of the oscillation.

show abstract

Heat advection processes leading to El Niño events as depicted by an ensemble of ocean assimilation products

et al. 2016

Self Cite

View full text Add to dashboard Cite

The oscillatory nature of El Niño‐Southern Oscillation results from an intricate superposition of near‐equilibrium balances and out‐of‐phase disequilibrium processes between the ocean and the atmosphere. The main objective of the present work is to perform an exhaustive spatiotemporal analysis of the upper ocean heat budget in an ensemble of state‐of‐the‐art ocean assimilation products. We put specific emphasis on the ocean heat advection mechanisms, and their representation in individual ensemble members and in the different stages of the ENSO oscillation leading to EN events. Our analyses consistently show that the initial subsurface warming in the western equatorial Pacific is advected to the central Pacific by the equatorial undercurrent, which, together with the equatorward advection associated with anomalies in both the meridional temperature gradient and circulation at the level of the thermocline, explains the heat buildup in the central Pacific during the recharge phase. We also find that the recharge phase is characterized by an increase of meridional tilting of the thermocline, as well as a southward upper‐ocean cross‐equatorial mass transport resulting from Ekman‐induced anomalous vertical motion in the off‐equatorial regions. Although differences between data sets are generally small, and anomalies tend to have the same sign, the differences in the magnitude of the meridional term are seen to be key for explaining the different propagation speed of the subsurface warming tendency along the thermocline. The only exception is GECCO, which does not produce the patterns of meridional surface Ekman divergence (subsurface Sverdrup convergence) in the western and central equatorial Pacific.

show abstract

On the dynamical mechanisms explaining the western Pacific subsurface temperature buildup leading to ENSO events

Cited by 14 publications

References 26 publications

Sensitivity of El Niño intensity and timing to preceding subsurface heat magnitude

Sensitivity of El Niño intensity and timing to preceding subsurface heat magnitude

Timing of subsurface heat magnitude for the growth of El Niño events

Heat advection processes leading to El Niño events as depicted by an ensemble of ocean assimilation products

Contact Info

Product

Resources

About