Separating the North and South Pacific Meridional Modes Contributions to ENSO and Tropical Decadal Variability

Liguori, Giovanni; Lorenzo, Emanuele Di

doi:10.1029/2018gl080320

Cited by 49 publications

(49 citation statements)

References 54 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For example, a reduction in the North Pacific off-equatorial trades in the boreal spring can trigger the winds-evaporations-SST (WES) thermodynamic feedback 36 resulting in ocean-atmosphere coupled anomalies that propagate into the tropics and can initiate ENSO in summer and fall. This process, first described in the context of the seasonal footprinting mechanism 33 , leads to coupled ocean-atmosphere Meridional Modes that have been shown to influence ENSO and tropical variability from both hemispheres independently 28,[37][38][39][40] . The weakening of the off-equatorial winds can also influence or trigger the development of ENSO-like variability by two ways.…”

Section: Mechanistic Hypothesis For Generating Tropical Low-frequencymentioning

confidence: 99%

The impacts of Extra-tropical ENSO Precursors on Tropical Pacific Decadal-scale Variability

Zhao

Lorenzo

2020

Sci Rep

Self Cite

View full text Add to dashboard Cite

Off-equatorial wind anomalies on seasonal timescales from both the North and South Pacific, known as "precursors" of the El Niño Southern Oscillation (ENSO), have been shown to independently trigger the ENSO feedbacks in the tropics and its teleconnections to the extra-tropics. However, the impacts of ENSO precursors on Tropical Pacific Decadal-scale Variability (TPDV) is still not well understood and quantified. We show that the dynamic sequence from extra-tropical ENSO precursors to ENSO (tropics) to extra-tropical ENSO teleconnections is not only important for ENSO, but acts as a primary mechanism to filter (e.g. reddening) the low-frequency variability of the seasonal precursors into the decadal-scale variance of the Pacific basin, accounting for the largest fraction of the TPDV (~65%) and its phase. This process, which contrasts previous theories advocating for a TPDV generated internally in the tropics (e.g. ENSO residuals), is inherently unpredictable and not well reproduced in climate models and raises challenges for understanding and predicting the role of internal tpDV in future climate change scenarios. Low-frequency variability of tropical Pacific climate on decadal and longer timescales, referred to in the literature and here as "decadal variability", is known to influence large-amplitude changes in marine ecosystems, climate and weather extremes over the Pacific Ocean, Asia and the Americas with important societal impacts 1-4. Furthermore, tropical Pacific decadal variability (TPDV) has been implicated as a driver of the global warming hiatus 5-8 , yet the mechanisms controlling its phase and predictability remain unclear. The spatial footprint of TPDV in global sea surface temperature anomaly (SSTa) can be extracted by correlating the time series of the dominant mode of 8-year lowpass SSTa in the tropical Pacific [10°S-10°N] with global SSTa (Fig. 1a) (see Methods). This approach is similar to previous characterization of basin-scale Pacific decadal variability (PDV), which uses the dominant mode of lowpass SSTa over the entire basin 9 (Fig. 1c). The TPDV and PDV patterns are not independent and exhibit very similar structures in the squared correlation explaining ~65% of the Pacific decadal variance (Fig. 1a vs. 1c). A comparison of the time series associated with the modes, hereinafter the TPDV and PDV indices (see Methods for exact definition), show significant correlation (R = 0.83, > 99% confidence level) suggesting that the tropics plays a key role in shaping the basin-scale Pacific decadal variance (Fig. 1e). This is further confirmed by the fact that the dominant modes of Pacific low-frequency variability extracted independently over the North and South Pacific, such as the Pacific Decadal Oscillation 10 , the North Pacific Gyre Oscillation 11 , and the South Pacific Decadal Oscillation 12 , are not independent in the low-frequency limit and all exhibit the spatial and temporal structure of the TPDV pattern 13. Given that the tropics is the main bridge between the North and South Pacific cl...

show abstract

Section: Mechanistic Hypothesis For Generating Tropical Low-frequencymentioning

confidence: 99%

The impacts of Extra-tropical ENSO Precursors on Tropical Pacific Decadal-scale Variability

Zhao

Lorenzo

2020

Sci Rep

Self Cite

View full text Add to dashboard Cite

show abstract

“…Outside this region, the model is fully coupled (e.g. Liguori and Di Lorenzo 2019). The last 200 years of both experiments are analyzed.…”

Section: Partially Coupled Experimentsmentioning

confidence: 99%

The influence of wintertime SST variability in the Western North Pacific on ENSO diversity

Fosu

Wang

2020

Clim Dyn

View full text Add to dashboard Cite

Sea surface temperature anomalies (SSTa) in the Western North Pacific (WNP) have been linked to the development of El Niño Southern Oscillation (ENSO) events a full year in advance. However, the contribution of the WNP precursor to the temporal evolution and spatial complexity of ENSO remains unclear. Using the preindustrial experiment of the Community Earth System Model as the control climate, a partially coupled experiment is conducted in which WNP SSTa are restored to the model climatology. By comparing the perturbed experiment to the control, we are able to clearly characterize ENSO's response to WNP SST variability. We find that the WNP is predominantly linked to eastern Pacific (EP) ENSO events. Without SST variability in the WNP, central Pacific (CP) ENSO events are more likely to develop. This variation in ENSO flavor is controlled by how the WNP projects onto wind stress anomalies in the western equatorial Pacific, which in turn impacts the discharge and recharge of ocean heat during the ENSO cycle. Specifically, the removal of SSTa in the WNP weakens the buildup of ocean heat in the western equatorial Pacific, which then hinders the development of EP-type events.

show abstract

“…There is evidence that TPV is linked to stochastic atmospheric forcing from the South Pacific 22 , and that climate models which have less subsurface variability in the Southern Tasman Sea exhibit less decadal variability in the Niño3.4 region in the central equatorial Pacific 23 . The North and South Pacific Meridional Modes (NPMM, SPMM) 24,25 have also been identified as important drivers of TPV on multi-year to decadal timescales 26 . The influence of the Atlantic Multidecadal Oscillation (AMO) on the Pacific has also been well documented 27–29 , with the AMO modulating the Walker circulation, leading to modified wind anomalies over the equatorial Pacific 27 .…”

Section: Introductionmentioning

confidence: 99%

The role of the South Pacific in modulating Tropical Pacific variability

Chung

Power

Sullivan

et al. 2019

Sci Rep

View full text Add to dashboard Cite

Tropical Pacific variability (TPV) heavily influences global climate, but much is still unknown about its drivers. We examine the impact of South Pacific variability on the modes of TPV: the El Niño-Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO). We conduct idealised coupled experiments in which we suppress temperature and salinity variability at all oceanic levels in the South Pacific. This reduces decadal variability in the equatorial Pacific by ~30% and distorts the spatial pattern of the IPO. There is little change to overall interannual variability, however there is a decrease in the magnitude of the largest 5% of both El Niño and La Niña sea-surface temperature (SST) anomalies. Possible reasons for this include: (i) reduced decadal variability means that interannual SST variability is superposed onto a ‘flatter’ background signal, (ii) suppressing South Pacific variability leads to the alteration of coupled processes linking the South and equatorial Pacific. A small but significant mean state change arising from the imposed suppression may also contribute to the weakened extreme ENSO SST anomalies. The magnitude of both extreme El Niño and La Niña SST anomalies are reduced, and the associated spatial patterns of change of upper ocean heat content and wind stress anomalies are markedly different for both types of events.

show abstract

Separating the North and South Pacific Meridional Modes Contributions to ENSO and Tropical Decadal Variability

Cited by 49 publications

References 54 publications

The impacts of Extra-tropical ENSO Precursors on Tropical Pacific Decadal-scale Variability

The impacts of Extra-tropical ENSO Precursors on Tropical Pacific Decadal-scale Variability

The influence of wintertime SST variability in the Western North Pacific on ENSO diversity

The role of the South Pacific in modulating Tropical Pacific variability

Contact Info

Product

Resources

About