Abstract
The Pacific Decadal Oscillation (PDO), the leading mode of Pacific decadal sea surface temperature variability, arises mainly from combinations of regional air-sea interaction within the North Pacific Ocean and remote forcing, such as from the tropical Pacific and the Atlantic. Because of such a combination of mechanisms, a question remains as to how much PDO variability originates from these regions. To better understand PDO variability, the equatorial Pacific and the Atlantic impacts on the PDO are examined using several 3-dimensional partial ocean data assimilation experiments conducted with two global climate models: the CESM1.0 and MIROC3.2m. In these partial assimilation experiments, the climate models are constrained by observed temperature and salinity anomalies, one solely in the Atlantic basin and the other solely in the equatorial Pacific basin, but are allowed to evolve freely in other regions. These experiments demonstrate that, in addition to the tropical Pacific’s role in driving PDO variability, the Atlantic can affect PDO variability by modulating the tropical Pacific climate through two proposed processes. One is the equatorial pathway, in which tropical Atlantic sea surface temperature (SST) variability causes an El Niño-like SST response in the equatorial Pacific through the reorganization of the global Walker circulation. The other is the north tropical pathway, where low-frequency SST variability associated with the Atlantic Multidecadal Oscillation induces a Matsuno-Gill type atmospheric response in the tropical Atlantic-Pacific sectors north of the equator. These results provide a quantitative assessment suggesting that 12–29% of PDO variance originates from the Atlantic Ocean and 40–44% from the tropical Pacific. The remaining 27–48% of the variance is inferred to arise from other processes such as regional ocean-atmosphere interactions in the North Pacific and possibly teleconnections from the Indian Ocean.
Highlights
The Pacific Decadal Oscillation (PDO) is the dominant low frequency climate variability in the North Pacific and is defined as the leading mode of North Pacific detrended sea surface temperature anomalies (SSTAs) ( 20◦–70◦N )1 3 Vol.:(0123456789)northern South America (Barlow et al 2001; Tanimoto et al 2003; McCabe et al 2004; Hu and Huang 2009; Zanchettin et al 2008; Wang et al 2009; Taguchi et al 2012; Wang et al 2014; Vance et al 2015)
We note the statistically significant correlations 11–12 years leading the PDO in the GLOB runs (Zhang and Delworth 2007; Wu et al 2011); these correlations disappear in the CESM and MIROC ATL runs where we find a local peak of correlations when the Atlantic Multidecadal Oscillation (AMO) leads the PDO by 9 months ( R = −0.77 and −0.36, respectively)
This study focuses on the North Pacific region, but the PDO is related to the Interdecadal Pacific Oscillation (IPO), which spans both northern and southern hemispheres
Summary
The Pacific Decadal Oscillation (PDO) is the dominant low frequency climate variability in the North Pacific and is defined as the leading mode of North Pacific detrended sea surface temperature anomalies (SSTAs) ( 20◦–70◦N ). Atlantic Ocean variability can affect the frequency and amplitude of ENSO events through tropical inter-basin interactions (Ham and Kug 2015), which subsequently influences the PDO through the atmospheric bridge (Alexander 1990) Consistent with this mechanism, Levine et al (2018) found that a positive Atlantic Multidecadal Oscillation (AMO) can favor a northward shift in the intertropical convergence zone (ITCZ) through changes in equatorial trade winds and precipitation anomalies, which affect tropical Pacific SSTs. A similar inter-basin connection through a zonal circulation, but in the mid-latitude region instead of the tropics, was proposed based on the mid-latitude sea level pressure (SLP) see-saw between the North Atlantic and North Pacific associated with the AMO (Sun et al 2017; Gong et al 2020). We describe impacts from the tropical Pacific (Sect. 4) and the Atlantic on the PDO (Sect. 5), followed by a discussion (Sect. 6) and concluding remarks (Sect. 7)
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