TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 65 (No. 6), pp. 737-756, 2009

Water Mass Variability in the Western North Pacific Detected in a 15-Year Eddy Resolving Ocean Reanalysis

Yasumasa Miyazawa1*, Ruochao Zhang1, Xinyu Guo1,2, Hitoshi Tamura1, Daisuke Ambe3, Joon-Soo Lee3, Akira Okuno3, Hiroshi Yoshinari3, Takashi Setou3 and Kosei Komatsu3,4

1Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokohama, Kanagawa 236-0001, Japan
2Center for Marine Environmental Studies, Ehime University, Matsuyama, Ehime 790-8577, Japan
3National Research Institute of Fisheries Science, Fisheries Research Agency, Yokohama, Kanagawa 236-8648, Japan
4Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8561, Japan

(Received 20 October 2008; in revised form 16 June 2009; accepted 26 June 2009)

Abstract: This paper describes a reanalysis of the variability of water mass properties and currents in the western North Pacific using an ocean forecast system, Japan Coastal Ocean Predictability Experiment 2 (JCOPE2), to provide the basic description and information about the quality for data users. We have created the reanalysis data with high horizontal resolution of 1/12° to describe the oceanic variability associated with the Kuroshio-Kuroshio Extension, the Oyashio, and the mesoscale eddies from 1993 to 2007. The products made by an eddy-resolving ocean model combined with the three-dimensional variational data assimilation well reproduced the mean water mass property in the western North Pacific and the interannual variations of the Kuroshio-Kuroshio Extension and the Oyashio coastal branch. From the reanalysis data, we found that both the mean kinetic energy of the Kuroshio Extension axis at the first meandering crest and southward intrusion of the Oyashio coastal branch were closely related with the horizontal distribution of both the Oyashio Water and North Pacific Intermediate Water within the appropriate interannual time scale. The reanalysis data also indicated that the north-south migration of the Kuroshio Extension associated with its regime transitions affected the decadal modulation of the Subtropical Mode Water formation in the recirculation gyre of the Kuroshio Extension.

*Corresponding author E-mail: miyazawa@jamstec.go.jp

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