Data and code from: Oceanic mesoscale eddies enhance the Pacific Decadal Oscillation and its predictability

The Pacific Decadal Oscillation (PDO) profoundly influences marine
ecosystems, fisheries, and global hydroclimate. While traditionally
interpreted as basin-scale oceanic responses to atmospheric stochastic
forcing, whether its dynamics involve active ocean feedbacks remains
unresolved. Using an unprecedented multi-century eddy-resolving global
climate simulation, we find that mesoscale eddy-driven atmospheric
anomalies in the Kuroshio Extension (KE) region are critical to PDO
evolution. During the PDO cold phase, the northward-shifted meandering KE
generates mesoscale sea surface temperature (SST) anomalies that intensify
the lateral diabatic heating gradient, driving deep updrafts that cool the
mid-troposphere and weaken its northern baroclinicity. This suppresses
transient eddy momentum flux and facilitates a basin-scale low-pressure
anomaly, initiating transition to the warm phase. Concurrently, mesoscale
eddy-induced vertical heat transport sustains SST anomalies, providing
additional PDO memory. These coupled processes substantially enhance the
PDO’s predictability. Our findings highlight the previously
underappreciated upscale effects of oceanic eddies, offering important
insight into decadal climate variability.