[A-CG32] Extratropical oceans and atmosphere

[ACG32-10] The Kuroshio Extension decadal variability and its remote climatic impacts: a key role for mesoscale ocean-atmosphere interaction

★Invited Papers

*Bolan Gan¹, Tianyu Wang¹, Lixin Wu^1,2, Bo Qiu³, Jianping Li¹, Haiyuan Yang¹, Li Zhang¹ (1.Ocean University of China, 2.Laoshan Laboratory, 3.University of Hawaii at Manoa)

Keywords:Ocean mesoscale eddies, Ocean-atmosphere interaction, Kuroshio Extension, Decadal variability

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 atmosphere obfuscate the understanding of its oscillatory nature at the preferred decadal timescale. Here, on the basis of physical process-oriented diagnoses using satellite observations and atmospheric reanalysis, a wintertime mesoscale ocean-atmosphere coupled delayed oscillator paradigm is proposed for the KE decadal variability. During a stable state of the KE system, the downstream KE transition region exhibits a prominent presence of mesoscale sea surface warming associated with warm eddies, which induces surface wind convergence and initial updraft through enhanced turbulent mixing. Meanwhile, the finer-scale increase of diabatic heating in the lower troposphere with abundant moisture supply from warmer water facilitates the deep-reaching updraft, which adiabatically cools the middle troposphere and subsequently drives southward deflection of atmospheric eddy available potential energy (EAPE) production by baroclinic conversion. Consequently, the synoptic eddy activity displaces southward across the basin with additional energy supply from the increased diabatic production of EAPE downstream. The resulting synoptic eddy forcing fosters a basin-wide equivalent-barotropic cyclonic circulation anomaly, which further drives negative sea surface height anomalies in the central basin. These anomalies then propagate westward into the upstream KE region after approximately 4 years, ultimately triggering an unstable state of the KE system. In the present coupled paradigm, the wintertime finer-scale thermodynamic response to mesoscale oceanic surface condition is a pivotal element. Such response also excites a Rossby wave train, leading to significant changes in surface air temperature and precipitation over the North Atlantic and adjacent area.