Decadal-scale influence of the Kuroshio and Oyashio extension fronts on atmospheric circulation and storm track

Abstract

Recent findings showed that midlatitude oceanic fronts in the Kuroshio-Oyashio Extension (KOE) region may significantly influence the overlying atmosphere on the interannual 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 interannual fluctuations of the KEF and OEF latitudinal position in a consistent way. It is found that the when the fronts meridionally migrate, response of the marine atmospheric boundary layer is remarkable. The response is mostly equivalent barotropic, with upper atmosphere intensification and sign reversal of temperature anomalies. Significant response of the storm track is also found. Diagnosis showed that eddy-mean flow feedback mediated by the storm track is responsible for the large-scale circulation changes, by means of both eddy heat flux and eddy vorticity flux. The spatial pattern of the KEF influence is a zonal dipole and the OEF is a monopole. The northward excursion of the KEF and OEF generally forces atmospheric responses with reverse sign. However, as the KEF and OEF moves in opposite directions with a lag time of 2.5 years, their atmospheric impacts sustains each other.