Title: Poleward Shift of the Pacific North Equatorial Current Bifurcation.

Journal: Journal of Geophysical Research: Oceans, doi: 10.1029/2019JC015019.

Authors: GUO H. -H., Z. -H. Chen*, and H. -Y. Yang

Abstract: The dynamics of the poleward shift of the Pacific North Equatorial Current bifurcation latitude (NBL) is studied using a 5.5‐layer reduced gravity model. It is found that the poleward shift of the NBL is associated with the asymmetric intensity of the wind stress curl input to the Pacific tropical and subtropical gyres. Stronger wind stress curl in the subtropical gyre leads to equatorward transport in the interior upper ocean across the boundary between the two gyres, causing a poleward transport compensation at the western boundary. In the lower layer ocean, in turn, there is poleward (equatorward) transport at the interior (western boundary) due to Sverdrup balance which requires zero transport at the gyre boundary where zonally integrated wind stress curl is zero. Therefore, the NBL exhibits a titling feature, with its position being more equatorward in the upper layer and more poleward in the lower layer. The equatorial currents bifurcations in other basins are also characterized by the poleward titling vertical structure. The wind stress curl over the subtropical gyre is generally stronger than that over the tropical gyre, resulting in the bifurcations shifting poleward with increasing depth.