Diagnostic Analysis of the Response of Volume Transport through the Tsushima Strait to the Eddy-Induced Variations in the Kuroshio Region

Abstract The Tsushima Strait (TS) is the sole passage for volume transport from the East China Sea to the Sea of Japan. To date, the process underlying the interannual variability in volume transport remains unclear. In this study, 27-yr (1993–2019) reanalysis data from the Japan Coastal Ocean Predictability Experiment 2 (JCOPE2M) system and in situ/satellite observations were employed to understand this process. The results suggest that TS transport was generally high in 1999, 2003/04, and 2010 and low in 1995/96, 2005/06, 2008, and 2014/15. The sea level anomaly (SLA) outside the entrance of the TS, that is, the upstream TS forcing, dominates the interannual TS transport variation. A high SLA pumps more water into the Sea of Japan via the TS, and vice versa. By synthesizing JCOPE2M reanalysis data and satellite observations, further analysis revealed that cyclonic mesoscale eddies from the subtropical countercurrent (STCC) could be responsible for this high SLA by reducing Kuroshio transport, enhancing Kuroshio intrusion across the shelf, and increasing the SLA around the upstream TS region. The reverse was true for anticyclonic STCC eddies. Variability in the Kuroshio intrusion southwest of Kyushu induces variations in the TS transport on an interannual time scale.