An Intermediate Current in Tropical North Pacific Observed by Moored Current Meters

Abstract

Six years of current meter observation from a subsurface mooring at 130°E, 8.5°N captured an eastward flow below the North Equatorial Undercurrent (NEUC) between 1,500 and 3,000 m. This flow, named Lower-NEUC, has mean velocity of 0.73 ± 0.08 cm/s and 1.05 ± 0.08 cm/s at 2,000 and 2,500 m, respectively. Its spatial distribution is studied using Argo absolute geostrophic velocity data and ocean reanalysis. In the northwestern Pacific, Lower-NEUC shifts poleward with increasing longitude and is wider in Argo absolute geostrophic velocity data (around 300 km) and narrower in reanalysis (around 150 km). Vertically, the core of Lower-NEUC lies mostly between 27.5 and 27.6${\sigma }_{\theta }$ in reanalysis, shallower compared to mooring observation. Reanalysis data shows L-NEUC's generation is connected to deep eddies. After proving that L-NEUC is not a result of averaging west-translating eddies, we showed that L-NEUC is generated by eddy potential vorticity flux convergence.