Measurement of the North Equatorial Current/Undercurrent by a subsurface mooring at 160°E

Abstract

ABSTRACT Based on the subsurface mooring observations at 159°59′E, 14°40′N from July 2014 to May 2016, the vertical structure and variability of the North Equatorial Current/Undercurrent (NEC/NEUC) are investigated. The NEC flows westward stably from the sea surface down to 500 m and is strongest with the magnitude of approximately 40 cm/s in January 2016, while in several months, the eastward current occurs and attains the maximum of nearly 15 cm/s in April and September 2015. Beneath the NEC, the eastward NEUC is observed and its depth could reach at least 860 m. The Power Spectral Density function reveals surface-intensified signals of the currents at mooring site, and the period in the upper layer is around 30–155 days. AVISO products accurately describe the variability of the NEC and are consistent with the mooring observations. Further analysis with sea level anomaly data suggests that the mesoscale eddies, which move westward, may influence the intraseasonal variability measured by the mooring. A comparison of the results with other mooring observations at 130°E implies the phenomenon of western intensification and the existence of NEUC jets at different longitudes that they are not observed at 130°E, 15.5°N.