Oceanic Processes of Tropical Pacific Decadal Variability, Revisited

Tropical Pacific Decadal Variability has been linked to the rate of change of globally-averaged surface temperature and modulates El Niño Southern Oscillation global impacts. Predicting decadal variations in the tropical Pacific is therefore critical, but our understanding of the mechanisms of TPDV and their predictability remains unclear. This presentation critically reviews the oceanic processes underpinning the mechanisms proposed for TPDV to assess their potential effectiveness and relative role. The 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; and the propagation of salinity-compensated temperature (“spiciness”) anomalies from the subtropics to the equatorial thermocline. While all of these processes are involved, to some degree, in the decadal variations of the tropical Pacific Ocean, the oceanic adjustment through wind-forced Rossby waves emerges as a key component of tropical Pacific decadal variability and its potential predictability. However, the origin of the wind forcing of TPDV remains a critical outstanding issue.