Abstract
The wind-driven transport and velocity structure are estimated from direct current measurements and geostrophic shears along a transpacific section at 10°N. The total velocity field is dominated by the North Equatorial Current and its eddies, while the shear features near-inertial oscillations and a wind-driven current spiral. The section-averaged cross-track ageostrophic shear can be approximated as a slab layer 30–40 m thick with a velocity of 0.05 m s−1 overlying a sheared layer in which the velocity goes to zero below 80 m. The resulting zonally integrated ageostrophic mass transport is 62 (±10) × 109 kg s−1 northward, similar to the estimate of 52 (±10) × 109 kg s−1 predicted by the Ekman balance using winds measured from the ship. Climatological winds yield similar transport. The zonally averaged velocity relative to the top of the thermocline forms a clockwise spiral, decaying with depth. As has been found at higher latitudes, this mean wind-driven spiral results from the diurnal cycling of the mixed layer depth.
