The Pacific Ocean subtropica cell surface limb

Abstract

The subtropical cells (STCs) cycle subtropically subducted water to the equator, where it upwells and flows poleward at the surface, exchanging heat and freshwater with the atmosphere. Pacific STC surface flow is analyzed using drifter data. Mean surface velocities are estimated. The mean divergence reveals substantial equatorial upwelling. Off-equatorial downwelling around ±4° latitude suggests that about half the upwelled water may recirculate in shallow tropical cells. Pathways and time scales for the poleward surface limb of the STC are estimated. Mean streamlines reach ±9° latitude after half a year and ±22° after 2 years, taking a more convoluted path in the northern hemisphere. They reenter the subtropics in the western half of the basin, far from the subduction regions feeding the equatorward limbs of the STCs, reinforcing the point that the STCs are intrinsically linked with the global ocean circulation.