Abstract
We analyzed the results of a high‐resolution global ocean circulation model with 1/4‐degree grid spacing and 55 vertical levels to investigate the structure and the mechanism of subsurface countercurrents (SCCs) in the equatorial Pacific Ocean. The model SCCs have observably similar structures; that is, they are associated with the pycnostad between 26.0 and 26.8σθ, deep in the west and shallow and in the east, and the densities in the SCCs' cores decrease from west to east. The volume transport in the density layer shows that each of the north SCC and the primary south SCC accompanies a westward current at their equator side; the SCC and the westward current comprise the recirculation gyre there. High mesoscale eddy activity results in a mean flow acceleration corresponding to the SCCs, especially to the north SCC in the eastern Pacific Ocean. The structures are consistent with the low potential vorticity (PV) in the equatorial region; thus the recirculations are suggested to be related with the homogenization of the PV in the equatorial region by eddy activity. In contrast, the secondary south SCC flows southeastward along the thickness front of the layer between 26.0 and 26.8σθ and ends near the coast around 11°S, 80°W. The coastal undercurrent and upwelling drain the water from it there. This suggests that the secondary south SCC is not a part of recirculation, but rather driven by force near the eastern boundary.
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