ABSTRACT

Significant decadal sea surface temperature (SST) variability (DSV) is observed in the Kuroshio-Oyashio Extension (KOE) region. A center of action is located in the subarctic frontal zone (SAFZ) near the date line. The present work approaches the physical mechanisms of DSV in the KOE region especially in the center of action, diagnosing and comparing long-term observations, assimilated data, and output from an ocean general circulation model. In the northern KOE region, large-scale ocean gyre circulation regulates the DSV through geostrophic advection with the upper ocean temperature anomalies largely in phase in the vertical. By contrast, atmospheric thermal forcing by local surface winds appears to dominate over ocean dynamical effects in the southern KOE region and to significantly modify the dominant spatial pattern of DSV from a meridional dipole that the ocean dynamics would otherwise generate into an observed monopole. The phase relationship between the effects of ocean dynamics and atmospheric thermal forcing is in-phase in the northern KOE region, while in the south, out-of-phase. The anomalous mixed layer depth and geostrophic current fields are preferable to determine the geographical location of the center of action in the SAFZ through ocean dynamical effects.