Enhanced wintertime turbulent heat flux along the northward shifted Kuroshio Extension during the Kuroshio large meander

Abstract The Kuroshio Extension (KE) is an area of intense heat exchange with the atmosphere in winter. The KE has moved significantly northward in the region east of Japan since the Kuroshio large meander (LM) began south of Japan in August 2017. In this study, we examined the variations of sea surface temperature (SST) and turbulent heat flux (THF; sum of sensible and latent heat fluxes) in the KE region for 29 winters from December 1993/February 1994 to December 2021/February 2022 using the third-generation data set of the Japanese Ocean Flux Data Sets with Use of Remote Sensing Observations (J-OFURO3). The northward-moving KE is accompanied by large positive SST anomalies along the KE current axis, especially around the first crest of the KE current, which leads to the remarkable increase in upward THF in the west Kuroshio-Oyashio confluence region. It is found that the positive SST anomalies are caused by strong warm advection due to the enhanced KE geostrophic current velocity. During the Kuroshio LM, the KE flows close to the coast off the Boso Peninsula with the narrow width, which increases the current speed of the KE. In addition, the anticyclonic circulation gyre south of the KE around the first crest is intensified, which is suggested to contribute to the enhanced KE current advection. Hydrographic observations revealed that the warm anomalies of the KE were not limited to the surface but extended down to the thermocline around 800 m depth southeast off the Boso Peninsula.