Naturally occurring tropical Pacific variations at timescales of 7–70 years — tropical Pacific decadal variability (TPDV) — describe basin-scale sea surface temperature (SST), sea-level pressure and heat content anomalies. Several mechanisms are proposed to explain TPDV, which can originate through oceanic processes, atmospheric processes or as an El Niño/Southern Oscillation (ENSO) residual. In this Review, we synthesize knowledge of these mechanisms, their characteristics and contribution to TPDV. Oceanic processes include off-equatorial Rossby waves, which mediate oceanic adjustment and contribute to variations in equatorial thermocline depth and SST; variations in the strength of the shallow upper-ocean overturning circulation, which exhibit a large anti-correlation with equatorial Pacific SST at interannual and decadal timescales; and the propagation of salinity-compensated temperature (spiciness) anomalies from the subtropics to the equatorial thermocline. Atmospheric processes include midlatitude internal variability leading to tropical and subtropical wind anomalies, which result in equatorial SST anomalies and feedbacks that enhance persistence; and atmospheric teleconnections from Atlantic and Indian Ocean SST variability, which induce winds conducive to decadal anomalies of the opposite sign in the Pacific. Although uncertain, the tropical adjustment through Rossby wave activity is likely a dominant mechanism. A deeper understanding of the origin and spectral characteristics of TPDV-related winds is a key priority.

Capotondi, A., McGregor, S., McPhaden, M.J. et al. Mechanisms of tropical Pacific decadal variability. Nat Rev Earth Environ 4, 754–769 (2023). https://doi.org/10.1038/s43017-023-00486-x

Figure 5. Atmospheric processes involved in tropical Pacific decadal variability. a, Regressions of sea surface temperature (SST; shading), sea-level pressure (contours) and surface wind anomalies on the North Pacific Meridional Mode (NPMM) index; the NPMM index is calculated as the first SST expansion time series of an SST-wind maximum covariance analysis (with Niño3.4 index influence removed) performed over 21S–32N, 175E–95W. b, As in panel a, but for the South Pacific Meridional Mode (SPMM); the SPMM index is calculated as the NPMM, but over 10S–35S, 180E–70W. c, Modelled multidecadal average atmospheric response to decadal Indian Ocean SST anomalies (bottom, shading; representing SST differences from 1999–2008 minus 1988–1998), including precipitation (bottom, contours; green indicates positive anomalies and purple indicates negative anomalies), surface winds (bottom, vectors), 10S–10N mean temperature (middle, shading) and vertical winds (middle, vectors; magnified by a factor of 300 to scale with the zonal wind), and 200 hPa geopotential height (top, shading) and winds (top, vectors). d, As in panel c, but the response to decadal Atlantic Ocean SST anomalies (1999–2014 minus 1982–1998). Atmospheric influences from the extratropical Pacific, Atlantic and Indian Oceans can modify Pacific equatorial winds and contribute to tropical Pacific decadal variability. SSTA, sea surface temperature anomaly.