The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

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 1500-3000m. The mean velocity of this flow at 2000m and 2500m are 0.73± 0.08cm/s and 1.05 ± 0.08 cm/s, respectively. Its spatial distribution is studied using Argo absolute geostrophic velocity data and ocean reanalysis. In the northwestern Pacific, this Lower-NEUC shifts poleward and is wider in Argo absolute geostrophic velocity data (around 300km) and narrower in reanalysis (around 150km). Vertically, the core of Lower-NEUC is shallower compared to observation, lies mostly between 27.5-27.6σθ  in reanalysis. 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.
 

Western Pacific, eddy-mean flow interaction, mooring observation