Mooring Measurements of Full-Depth Zonal Currents along the 143E Meridian in the Northwestern Pacific Ocean

Full-depth ocean zonal currents in the tropical and extratropical northwestern Pacific (TNWP) are studied using current measurements from 17 deep-ocean moorings deployed along the 143 degrees E meridian from the equator to 22 degrees N during January 2016-February 2017. Mean transports of the North Equatorial Current and North Equatorial Countercur-rent are estimated tobe 42.7 +/- 7.1 Sv (1 Sv ; 106 m3 s21) and 10.5 +/- 5.3 Sv, respectively, both of which exhibit prominent annual cycles with opposite phases in this year. The observations suggest much larger vertical extents of several of the ma-jor subsurface currents than previously reported, including the Lower Equatorial Intermediate Current, Northern Interme-diate Countercurrent, North Equatorial Subsurface Current, and North Equatorial Undercurrent (NEUC) from south to north. The Northern Subsurface Countercurrent and NEUC are found to be less steady than the other currents. Seasonal variations of these currents are also revealed in the study. In the deep ocean, the currents below 2000 m are reported for the first time. The observations confirm the striation patterns of meridionally alternating zonal currents in the intermediate and deep layers. Further analyses suggest a superposition of at least the first four and two baroclinic modes to represent the mean equatorial and off-equatorial currents, respectively. Meanwhile, seasonal variations of the currents are generally dominated by the first baroclinic mode associated with the low-mode Rossby waves. Overall, the above observational re-sults not only enhance the knowledge of full-depth current system in the TNWP but also provide a basis for future model validation and skill improvement.