Intraseasonal variability of the Kuroshio observed via mooring at 18°N

Abstract

Insufficient observations near the origin of the Kuroshio have led to incomplete understanding of the intraseasonal variability (ISV) of the Kuroshio. Direct measurements of the Kuroshio velocity were performed with an array of three profiler moorings (122.7°E, 123°E, and 123.3°E) along 18°N from January 2018 to February 2020. The ISV of the Kuroshio at 18°N was investigated based on a combination of mooring observations and global high-resolution HYbrid Coordinate Ocean Model reanalysis data. The estimated time-averaged transport in the upper 350 m across the observation transect was 6.5±2.6 Sv (1.0 Sv=10⁶ m³/s). Two significant ISV peaks at 50–60 and ∼100 d were recognized in the power spectra of the meridional velocity and transport. Further analysis indicated that the ISV at 50–60 d was caused by westward-propagating eddies at average propagation speed of ∼13 cm/s and wavelength of ∼635 km. Another ISV peak at ∼100 d was mainly caused by northward-propagating eddies generated in the North Equatorial Current region. Further investigation indicated that the ISV of the Kuroshio at 18°N is dominated by meridional transport, rather than by the zonal migration of the Kuroshio main axis. Our findings provide a better understanding of the ISV of the Kuroshio east of Luzon Island.