Interdecadal variability in pan-Pacific and global SST, revisited

Area of Science:

• Climate Science
• Oceanography
• Atmospheric Science

Background:

• Recent surge in interest regarding the Interdecadal Pacific Oscillation (IPO) and its potential role in global surface temperature variations.
• Hypothesized link between the Pacific Ocean's low-frequency modulation of El Niño-Southern Oscillation (ENSO) and observed global temperature changes.
• Conventional definition of IPO relies on empirical orthogonal function (EOF) analysis of low-pass filtered sea surface temperature (SST), which introduces mathematical complexities like mode mixing.

Purpose of the Study:

• To clarify the nature of the Interdecadal Pacific Oscillation (IPO) and its relationship with other climate modes.
• To investigate the components contributing to the perceived IPO using unfiltered SST data and advanced analytical techniques.
• To determine the geographical origin and dominant modes of low-frequency variability in global and pan-Pacific SST.

Main Methods:

• Utilized pairwise rotated EOFs on unfiltered global SST data to separate high and low-frequency climate signals.
• Compared results from rotated EOF analysis with traditional EOF analysis of low-pass filtered SST data.
• Analyzed the composition of the leading principal component (PC) of filtered global SST, commonly identified as IPO.

Main Results:

• The leading dynamical modes of unfiltered global SST, after accounting for global warming, are ENSO, PDO, and AMO; IPO is not identified as a distinct mode.
• The leading PC of low-pass filtered global SST, often termed IPO, is a composite of ENSO, PDO, and AMO, varying with filter thresholds.
• The dominant mode in filtered global SST is the AMO, suggesting the term 'Interdecadal Pacific Oscillation' is a misnomer; filtered pan-Pacific SST is primarily driven by PDO.

Conclusions:

• The Interdecadal Pacific Oscillation (IPO) is not an independent climate mode but rather a mixture of ENSO, PDO, and AMO.
• The leading component of filtered global SST variability, commonly referred to as IPO, is predominantly the Atlantic Multidecadal Oscillation (AMO).
• Low-frequency variability originating from the Pacific (PDO and ENSO contributions) exhibits a near-zero global mean, challenging its role as the primary driver of global interdecadal temperature changes attributed to IPO.