Influence of SST on the Wintertime Turbulent Heat Fluxes in the Kuroshio-Oyashio Confluence Region

Variations of wintertime (January to March) turbulent (sensible and latent) heat fluxes are investigated using the Objectively Analyzed air-sea Fluxes (OAFlux) dataset of 1958–2006. The turbulent heat fluxes have large temporal variance in the Kuroshio-Oyashio Confluence (KOC) region [142°–155°E, 35°–40°N]. The turbulent heat fluxes in the KOC region also show a remarkable positive trend, the value of which in the recent decade increases by up to 20% from the climatological mean value (286 W m-2). In the present study, in order to seek for the cause of temporal behaviors of the turbulent heat fluxes, de-trended variables are used in the later analysis. The turbulent heat fluxes have significant positive correlations with variations of the surface wind speed over the KOC region, and with sea surface temperature (SST): a huge amount of heat is released from the ocean to the atmosphere when the SST takes positive anomaly. By the inspection to the satellite altimetry-derived sea surface height (SSH) dataset of 1993–2006, it is inferred that the SST variations in the KOC region result from activities of anticyclonic (warm) eddies which are detached from the Kuroshio Extension: the SST anomaly tends to be higher when the eddy kinetic energy level in the KOC region becomes higher, and vice versa. A multiple regression analysis using wind speed and SST anomalies in the KOC region as explanatory variables, shows that the SST formed as a result of anticyclonic eddy activities gives a significant impact to about half of the surface wind variations on the wintertime turbulent heat fluxes in the KOC region. The present results imply that upper oceanic condition including eddy activities in the KOC region can influence potentially on wintertime heat release of the ocean.