Reversal of Kuroshio‐Oyashio Extension SST Anomalies Between Early‐ and Late‐Autumn Is Primarily Driven by Atmospheric Variability

Abstract Mid‐latitude Kuroshio‐Oyashio extension sea surface temperature (SST KOE ) modulates climate extremes, affecting coastal and insular humans. However, unconcern about the subseasonal variability of SST KOE substantially existed in previous studies. We first systematic exposed that the phase reversals of SST KOE anomalies are an intrinsic and objective phenomenon, that is, the persistently warm SST KOE anomalies in early‐autumn turns to cool in late‐autumn, and vice versa. This SST KOE anomalies reversals, occurring in one‐quarter of years, accompanied by subsurface thermal, gradients and marine heatwaves undergo great changes in early‐ and late‐autumn. Utilizing observations and ocean model intercomparison project simulations, the impacts of atmospheric and oceanic variability were separated, and SST KOE anomalies reversal was found to be mainly due to the atmospheric forcing. Specifically, the local anticyclonic circulation anomalies in early‐autumn enhanced the sinking motion and shortwave radiation, thus heating the sea surface. In late‐autumn, this region shifted to cyclonic circulation anomalies control, with enhanced cold ocean currents and increased cloudiness suppressing shortwave radiation, leading to SST KOE reversal. The phase reversal of SST KOE anomalies not only alters the ocean seasonality, but may also provide new predictors for mid‐ and low‐latitude extreme climate prediction.