Temporal variations of the net Kuroshio transport and its relation to atmospheric variations |
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Authors: | Shusaku Sugimoto Kimio Hanawa Kumiko Narikiyo Megumi Fujimori Toshio Suga |
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Institution: | (1) Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation, Kawaguchi, Saitama, 332-0012, Japan;(2) Center for Environmental Research, Ocean Research Institute, The University of Tokyo, Nakano-ku, Tokyo, 164-8639, Japan;(3) Division of Oceanic and Atmospheric Science, Graduate School of Environmental Earth Science, Hokkaido University, Sapporo, 060-0810, Japan; |
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Abstract: | Temporal variations of the net Kuroshio transport are investigated using long-term hydrographic data from repeat section of
the 137°E meridian from the south of Japan (34°N) to New Guinea (1°S) conducted by the Japan Meteorological Agency. In this
study, boundaries of the Kuroshio and the Kuroshio Counter Current (KCC) are defined based on the sea surface dynamic height
distribution. Westward flows associated with the KCC and cold-core eddy north of the Kuroshio are removed from the eastward
flow associated with the Kuroshio in order to estimate the net Kuroshio transport strictly. The net Kuroshio transport reveals
low-frequency variations: significant signals on a decadal (about 10-year) timescale. The variations of net Kuroshio transport
are predominantly caused by changes in the magnitude of oceanic current speed fields associated with a vertical movement of
the main pycnocline depth around the southern boundary of the Kuroshio: deepening of the main pycnocline around the southern
boundary of the Kuroshio forms a sharp northern upward-tilting slope of the isopycnal surfaces at the Kuroshio region, and
eventually the net Kuroshio transport increases together with the Kuroshio eastward transport. By using a wind-driven hindcast
model, it is found that the main pycnocline depth variation results from the first-mode baroclinic Rossby waves attributable
to two types of Aleutian Low (AL) changes: a change in the magnitude of AL and meridional movement of AL. |
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