Synoptic observation of Central Mode Water in its formation region in spring 2003
Hydrographic data east of Japan from five research cruises and Argo profiling floats in spring 2003 have been analyzed to examine the relationship of the formation of Central Mode Water (CMW) and Transition Region Mode Water (TRMW) in late winter 2003 to thermohaline fronts and mesoscale eddies. TRMW and the denser variety of CMW (D-CMW) were formed continuously just south of the subarctic frontal zone between 155°E and 165°W with little relation to eddies, suggesting that the absence of the permanent thermocline and halocline in this area is essential for the formation. The lighter variety of CMW (L-CMW) was formed south of the Kuroshio bifurcation front and east of 165°E, partly in an anticyclonic eddy associated with the Kuroshio Extension. Some portion of D-CMW and L-CMW likely had been subducted to the permanent pycnocline by crossing southward the Kuroshio bifurcation front and the Kuroshio Extension front, respectively. In contrast, the formation of these waters in the western regions was inactive and was significantly different from that described previously using multiyear Argo float data. West of 155°E, TRMW and D-CMW were formed only in two anticyclonic eddies that had been detached from the Kuroshio Extension 1–2 years ago. L-CMW was hardly formed west of 165°E, which might be related to the upstream Kuroshio Extension being in its stable state characterized by low regional eddy activity.
KeywordsCentral Mode Water Formation Fronts Mesoscale eddies Decadal variability
The authors are grateful to the captain, crew, and scientists participating in the R/V Kofu-maru 0304 cruise, the R/V Seifu-maru 0304 cruise, and the R/V Ryofu-maru 0306 cruise of the Japan Meteorological Agency, the R/V Hakuho-maru KH-03-1 cruise of the Ocean Research Institute, The University of Tokyo, and the R/V Shoyo-maru FY2003 1st research cruise of the Fisheries Research Agency for their efforts in conducting the CTD and XCTD measurements. They also thank Tsuyoshi Ohira for his assistance in preparing the Argo float data and two anonymous reviewers for their helpful comments. The Argo float data used in this study were collected and made freely available by the International Argo Project and the national programs that contribute to it (http://www.argo.ucsd.edu, http://argo.jcommops.org). This study was initiated in 2005 when E.O. was sent from Institute of Observational Research for Global Change, Japan Agency for Marine-Earth Science and Technology to Scripps Institution of Oceanography (SIO) as a visiting scholar. He thanks the late Nobuo Suginohara and Nobuyuki Shikama for giving him an opportunity to visit SIO. This study is supported by the Japan Society for Promotion of Science (KAKENHI, Grant-in-Aid for Scientific Research (B), No. 21340133 and 25287118) and the Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT; Grant-in-Aid for Scientific Research on Innovative Areas under Grant No. 22106007 and 25121502). Comments from participants at the “Research Meetings on Air-Sea Interaction” in 2011−2013 held as a part of the Collaborative Research Program of Hydrospheric Atmospheric Research Center, Nagoya University and at the research meeting “North Pacific Ocean Circulation and the Changes” in 2013 supported by the Atmosphere and Ocean Research Institute, The University of Tokyo and the Marine Meteorological Society of Japan were helpful.
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