Decadal to Long-Term Variation of Hydrographic Properties in the Kuroshio Extension Region and the Kuroshio-Oyashio Confluence From 1993 to 2022

Large-scale atmospheric forcing drives the decadal to long-term variation of the Kuroshio Extension (KE) system, and it is of great significance to study the long-term change to understand how the KE system responds to global climate change. Using the satellite data from 1993 to 2022, this study investigated the regional thermal and dynamical characteristics and mesoscale eddy variation of the KE system and the Kuroshio-Oyashio Confluence (KOC) in the two periods before and after 2010. The results show that before 2010, the KE system is primarily dominated by two unstable states with relatively long time span and strong intensity. During the period of instability, more anticyclonic eddies are detached northward, transmitting signals from the KE region into the KOC region. After 2010, the long-term variation of the KE system is dominant, which is mainly manifested in the overall northward shift of the KE path, corresponding to the increase in sea surface temperature anomaly (SSTA) and sea surface height anomaly (SLA), and the eastward and southward flows near the two meanders upstream of the KE become moderate. During this period, the SSTA and SLA in the KOC region also had similar characteristics. After 2010, driven by the negative wind stress curl anomaly in the mid-latitudes of the North Pacific, the negative phase of the Pacific Decadal Oscillation (PDO) starts to dominate, resulting in significant positive anomalies of SLA and SSTA in the central North Pacific. This ocean signal is transmitted to the Northwest Pacific Ocean and dominates the variation of hydrographic properties in the KE-KOC region. The long-term variation of the difference after 2010 still requires verification on a longer time scale, which also offers an effective reference for the future prediction of the Kuroshio Extension model.