Time-Depth Variations of Equatorial Currents in the Western Pacific Directly Observed by Subsurface Moorings

The time-depth variations of surface, subsurface and intermediate equatorial currents in the western Pacific were directly measured by two acoustic Doppler current profiler moorings at 2°N and 4.7°N, 140°E during January-August 2014. The mean structure and variability of the North Equatorial Countercurrent (NECC), northern branch of the South Equatorial Current (SEC), Equatorial Undercurrent (EUC), Equatorial Intermediate Current (EIC), North Intermediate Countercurrent (NICC) and North Equatorial Subsurface Current (NESC) are studied in detail by combining the mooring measurements with the numerical model results and satellite observations. Compared with previous studies mainly based on shipboard synoptic surveys, the 8-month time series of velocity profiles reveal much larger vertical ranges of SEC and NESC, the deeper EIC and NICC, and much larger velocities of NICC and NESC. The new observation captures the reversals of the EIC in May and the NESC in June from westward to eastward. Significant intra-seasonal variations of the NECC, EUC, EIC, NICC and NESC are observed, and the combined variability in current axis and intensity are found to determine the measured intra-seasonal variations of the NECC, EUC and EIC. During January-April 2014, the NECC is found to be almost at its southernmost position and weakest over the past twenty years, possibly associated with the fickle El Niño of 2014.