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Pathways of the North Pacific Intermediate Water identified through the tangent linear and adjoint models of an ocean general circulation model
Author(s) -
Fujii Yosuke,
Nakano Toshiya,
Usui Norihisa,
Matsumoto Satoshi,
Tsujino Hiroyuki,
Kamachi Masafumi
Publication year - 2013
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/jgrc.20094
Subject(s) - ocean gyre , seamount , oceanography , water mass , ocean current , geology , current (fluid) , advection , ridge , subtropics , climatology , paleontology , fishery , physics , biology , thermodynamics
This study develops a strategy for tracing a target water mass, and applies it to analyzing the pathway of the North Pacific Intermediate Water (NPIW) from the subarctic gyre to the northwestern part of the subtropical gyre south of Japan in a simulation of an ocean general circulation model. This strategy estimates the pathway of the water mass that travels from an origin to a destination area during a specific period using a conservation property concerning tangent linear and adjoint models. In our analysis, a large fraction of the low salinity origin water mass of NPIW initially comes from the Okhotsk or Bering Sea, flows through the southeastern side of the Kuril Islands, and is advected to the Mixed Water Region (MWR) by the Oyashio current. It then enters the Kuroshio Extension (KE) at the first KE ridge, and is advected eastward by the KE current. However, it deviates southward from the KE axis around 158°E over the Shatsky Rise, or around 170°E on the western side of the Emperor Seamount Chain, and enters the subtropical gyre. It is finally transported westward by the recirculation flow. This pathway corresponds well to the shortcut route of NPIW from MWR to the region south of Japan inferred from analysis of the long‐term freshening trend of NPIW observation. Copyright © 2013 John Wiley & Sons, Ltd.