Formation and Circulation of Mode Waters of the North Pacific in a High-Resolution GCM

Abstract

Abstract Formation and circulation of mode waters in the subtropical North Pacific are investigated by performing a numerical simulation with a high-resolution general circulation model. In the model, important features for forming mode waters, such as separation of western boundary currents, frontal systems, mixed layer processes, and eddy activities, are well reproduced. Annual subduction rates, calculated by following the mixed layer base, have major peaks in three density ranges and are related to the deep winter mixed layer at the south of the fronts in the western North Pacific, that is, the Kuroshio Extension with a winter surface density of 25.5 σθ, the Kuroshio bifurcation front (26.2 σθ), and the subarctic front (26.5 σθ). The lightest peak corresponds to the Subtropical Mode Water (STMW). It is formed at the south of the Kuroshio Extension and enters the main pycnocline as it crosses the mixed layer depth (MLD) front to the south. The remaining two peaks correspond to the Central Mode Water (CM...