[A-CG30] Extratropical oceans and atmosphere

[ACG30-07] Dominant forcing regions of decadal variations in the Kuroshio Extension revealed by a linear Rossby wave model

*Yukito Tamura¹, Tomoki Tozuka¹ (1.The University of Tokyo)

Keywords:Kuroshio Extension, decadal variability, Rossby wave, sea surface height, North Pacific

The Kuroshio Extension (KE) is an intense eastward oceanic jet in the midlatitude western North Pacific. Due to active ocean-atmosphere interactions over the strong oceanic front associated with the KE, the area may be a key region for basin-scale Pacific climate variability. Satellite altimeters and eddy-resolving ocean models have revealed that the KE undergoes large decadal variations between a stable state and an unstable state, especially after the 1976/77 climate regime shift. Although previous studies suggested that baroclinic Rossby waves induced in the central and/or eastern North Pacific reach the KE and influence the KE decadal variability, it is still unclear where and how decadal surface atmospheric forcing anomalies that excite the Rossby waves are generated. In this study, using a linear Rossby wave model forced by reanalysis surface wind stress, the relative contribution of wind stress at each longitude is quantitatively investigated for the first time. It is shown that the wind forcing in the central North Pacific around 160°-150°W makes the largest contribution to the KE decadal variability. Further analyses suggest that the anomalous atmospheric forcing is caused by El Niño/Southern Oscillation (ENSO) Modoki via an atmospheric teleconnection, and the statistically significant relationship between the KE and ENSO Modoki appears only after the regime shift.