A Mesoscale Ocean–Atmosphere Coupled Pathway for Decadal Variability of the Kuroshio Extension System

Abstract The Kuroshio Extension (KE) system has been observed to experience a decadal cycle between dynamically stable and unstable states. However, divergent conclusions on its interaction with the atmosphere obfuscate understanding of oscillatory nature at preferred time scale. Here, using satellite observations ERA-Interim reanalysis in 2002–16, physical process-oriented diagnoses suggest that wintertime finer-scale thermodynamic response mesoscale oceanic surface conditions slow Rossby wave adjustment frame coupled ocean–atmosphere delayed oscillator for KE variability. During state system, downstream transition region is rich warming associated warm eddies, which induces wind convergence upward motion, probably via enhanced turbulent mixing. Meanwhile, increased diabatic heating lower troposphere abundant moisture supply from warmer water likely facilitates deep-reaching updraft adiabatically cools middle troposphere. background northwesterly helps spread out cooling, leading southward deflection local atmospheric eddy available potential energy (EAPE) production by baroclinic conversion. Consequently, synoptic activity displaces across basin additional EAPE downstream. Anomalous thermal vorticity forcing eventually fosters basin-scale equivalent-barotropic cyclonic circulation anomaly, further maintained conversion state. resultant wind-driven negative sea height anomalies propagate westward into upstream delay ∼4 years can trigger system.