Decadal‐Scale Influence of the Kuroshio and Oyashio Extension Fronts on Atmospheric Circulation and Storm Track

Abstract

AbstractRecent findings showed that midlatitude oceanic fronts in the Kuroshio‐Oyashio Extension (KOE) region may significantly influence the overlying atmosphere on the decadal timescale. However, the exact mechanism and the combined effects of both the Kuroshio Extension Front (KEF) and the Oyashio Extension Front (OEF) are still largely unknown. Here we use front‐resolving ERA5 reanalysis data to investigate the characteristics and mechanisms of the atmospheric response to decadal fluctuations of the KEF and OEF in a consistent way. It is found that the atmospheric response is equivalent barotropic with upper‐level intensification in terms of both basic flow and storm track. The geopotential height and storm track responses over western subpolar North Pacific are of opposite signs driven by intensifying KEF and OEF. Diagnosis showed that eddy vorticity feedback is responsible for the basic flow response at upper levels, whereas direct linear response to surface thermal forcing dominates at lower levels. The upper‐level eddy response is realized by midlevel diabatic conversion which is forced by changes of near‐surface background baroclinicity. In total, the decadal modulation by the KEF and OEF explains 19% (12%) of the variance of geopotential height (storm track) variability at 250 hPa (500 hPa), which is much higher than found in previous studies, presumably due to the higher resolution and the consideration of both fronts.