Mooring observations of equatorial currents in the upper 1000 m of the western Pacific Ocean during 2014

Abstract

Abstract Time‐depth variations of the equatorial currents over the upper 1000 m depth in the western Pacific Ocean were directly measured by acoustic Doppler current profiler moorings at 2°N, 140°E and 4.7°N, 140°E during January–August 2014. Intraseasonal variations of the equatorial currents, with periods of 37–73 days, were observed encompassing 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). Compared with previous studies based mainly on shipboard synoptic surveys, the 8‐month time series of velocity profiles provided direct evidence for the existence of NESC, captured reversals of the EIC in May and the NESC in June from westward to eastward direction, and revealed larger vertical extensions of the SEC and NESC and greater depths of the EIC and NICC than previously thought. According to a global analysis product of ocean surface current, during January–April 2014, the NECC was located around its southernmost position and with its the weakest intensity over the past 20 years. Some of the anomalous characteristics of these flows may be related to the fickle El Niño of 2014.