Pacific Decadal Oscillation: Tropical Pacific Forcing versus Internal Variability

Zhang, Yu; Xie, Shang‐Ping; Kosaka, Yu; Yang, Jun‐Chao

doi:10.1175/jcli-d-18-0164.1

Cited by 54 publications

(54 citation statements)

References 49 publications

(53 reference statements)

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“…2c). The oceanic response to these ENSO teleconnections is known to energize the North and South Pacific decadal variability oceanic modes [16][17][18][19][20][21] . Given the role of ENSO in driving these teleconnection patterns, indices of the north and south teleconnection patterns in JFM + 1 (see Methods) are no longer independent and share a significant correlation (R = 0.61, > 99% confidence level).…”

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

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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...

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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

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“…While midlatitude atmosphere has strong internal variability and is significantly influenced by the tropical sea surface temperature (SST), its response to the local SST is relatively weak and remain obscure (Battisti et al, 1995;Kushnir et al, 2002;Latif & Barnett, 1994;Mantua & Hare, 2002;Newman et al, 2016;Zhang et al, 2018). Nevertheless, it is necessary and fundamental to reveal the atmospheric response to the midlatitude North Pacific SST anomalies, especially for the ocean-atmosphere interaction mechanism in understanding the Pacific Decadal Oscillation (PDO), the distinctly decadal-to-interdecadal signal in the North Pacific (Deser et al, 2004;Enfield & Mestas-Nuñez, 1999;Mantua et al, 1997;Minobe, 1997;Zhu & Yang, 2003).…”

Section: Introductionmentioning

confidence: 99%

The Asymmetric Atmospheric Response to the Midlatitude North Pacific SST Anomalies

2019

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Forced by Pacific Decadal Oscillation‐related sea surface temperature (SST) anomalies with the same pattern but opposite signs in the western‐central North Pacific, nonlinear wintertime atmospheric responses are produced by a state‐of‐the‐art atmospheric general circulation model (GFDL AM2.1); that is, an obvious equivalent barotropic geopotential low appears over the cold SST forcing (“CSST”), whereas a weak baroclinic structure shows up corresponding to the warm SST forcing (“WSST”), and both of them have similar characteristics in the lower troposphere. Specifically, because of the relatively dry environment in the central North Pacific, nonlinear responses of moisture process including latent heat flux and low‐level atmosphere moisture advection induce asymmetric diabatic heating (Qd): in WSST, Qd tends to increase in the middle‐lower troposphere but decrease in the middle‐upper level, whereas it always increases in the whole troposphere in CSST. Thus, Qd has the same low‐level positive vertical gradient in both CSST and WSST, which produces similar atmospheric circulation anomalies in the lower troposphere. In turn, the asymmetric responses of low‐level temperature advection further modify air temperature meridional gradient as well as atmospheric baroclinicity in the lower troposphere, significantly shifting the transient eddy activities southward in CSST and greatly weakening their intensity in WSST, respectively. Accordingly, the transient eddy vorticity forcing primarily determines the upper‐level atmospheric responses in CSST, but it has unsystematic effects in WSST that are overtaken by Qd. Therefore, the dominance of diabatic heating in WSST and transient eddy forcing in CSST over the central North Pacific lead to the asymmetric atmospheric responses among which the asymmetry of moisture plays an essential role.

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“…between global and regional wind speeds over land and decadal changes in global ocean/atmosphere oscillations; (3) recovered terrestrial wind speed explains much of the increase in U.S. wind power capacity over the last decade. These recent phases of the ocean/atmosphere oscillations are likely to continue for at least another decade (references 22,24,25,27,35). Consequently, these changes are promising for future wind power generation in that time period.…”

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confidence: 99%

A reversal in global terrestrial stilling and its implications for wind energy production

et al. 2019

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Wind power is a rapidly growing alternative energy source to achieve the goal of the Paris Agreement under the United Nations Framework Convention on Climate Change, to keep warming well below 2 •C by the end of the 21 st century. Widely reported reductions in global average surface wind speed since the 1980s, known as terrestrial stilling, however, have gone unexplained and have been considered a threat to global wind power production. Our new analysis of wind data from in-situ stations worldwide now shows that terrestrial stilling reversed around 2010 and global wind speeds over land have recovered most of the losses since the 1980s. Concomitant increased surface roughness from forest growth and urbanization cannot explain prior stilling. Instead we show decadal-scale variations of nearsurface wind are very / quite likely caused by the natural, internal decadal ocean/atmosphere oscillations of the Earth's climate system. The wind strengthening has increased the amount of wind energy entering turbines by 17 ±2% for 2010-2017, likely increasing U.S. wind power capacity by 2.5%. The increase in global terrestrial wind bodes well for the immediate future of wind energy production in these regions as an alternative to fossil fuel consumption. Projecting future wind speeds using ocean/atmosphere oscillations show wind turbines could be optimized for expected wind speeds, including small and large speeds, during the productive life spans of the turbines. Reports of a 8% global decline in land surface wind speed (~1980 to 2010) have raised concerns about output from future wind power 1-5. Wind power varies with the cube of wind speed (u) 6. The decline in wind speed is evident in the northern mid-latitude countries where the majority of wind turbines are installed including China, the U.S. and Europe 1. If the observed 1980-2010 decline in wind speed continued until the end of the century, global u would reduce by 21%, halving the amount of power available in the wind. Understanding the drivers of this long-term decline in wind speed is critical not merely to maximize wind energy production 9-11 but also to address other globally significant environmental problems related to stilling, including reduced aerosol dispersal, reduced evapotranspiration rates, and adverse effects on animal behavior and ecosystem functioning 1,3,4,12. The potential causes for the global terrestrial stilling are complex and remain contested (e.g.,

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Pacific Decadal Oscillation: Tropical Pacific Forcing versus Internal Variability

Cited by 54 publications

References 49 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 Asymmetric Atmospheric Response to the Midlatitude North Pacific SST Anomalies

A reversal in global terrestrial stilling and its implications for wind energy production

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