Variations of the Kuroshio in the Luzon Strait Revealed by EOF Analysis of Repeated XBT Data and Sea‐Level Anomalies

The Kuroshio in the Luzon Strait (KLS) has long been a focus of research for its complex ocean dynamics; however, it is poorly understood owing to a lack of long‐term in situ observations. Empirical orthogonal function (EOF) analyses were applied to quarterly expendable bathythermograph data (XBT, with a spatial resolution of 10–20 km in the Kuroshio region and 33 km in the other regions) and sea‐level anomaly (SLA) data, to examine the variations of the KLS. The first EOF modes of water temperature and SLA represent seasonal variations. The volume transport of the KLS referring to a 700 m depth reaches its maximum in warm months (19.4 Sv, July–September) and its minimum in cold months (17 Sv, January–March). This variation is similar to that east of Taiwan but is opposite to that east of Luzon, although the Luzon Strait is only 2° distant from the area east of Luzon. The outflow (1.3 Sv) from the South China Sea (SCS) to the Kuroshio in the warm months and the Kuroshio intrusion into the SCS in the cold months are responsible for this seasonal contrast. The second EOF modes of water temperature and SLA are related to the latitudinal movement of the Kuroshio recirculation on a time scale of 2–24 months. Lag correlation and wavelet analysis demonstrate that this mode is triggered by the westward‐propagating SLA along 21°–24°N and is affected by the downstream propagation of low‐frequency variation (mostly annual to biennial) from the North Equatorial Current bifurcation area.