Journal of Oceanography, Vol. 66 (No. 5), pp. 611-619, 2010
Shusaku Sugimoto1,2*, Kimio Hanawa1, Kumiko Narikiyo1, Megumi Fujimori1 and Toshio Suga1
1Department of Geophysics, Graduate School of Science, Tohoku University, Aramaki-aza-Aoba, Aoba-ku, Sendai 980-8578, Japan
2Institute for International Advanced Interdisciplinary Research, International Advanced Research and Education Organization, Tohoku University, Aramaki-aza-Aoba, Aoba-ku, Sendai 980-8578, Japan
(Received 22 May 2009; in revised form 7 June 2010; accepted 12 June 2010)
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.