Roles of mode waters in the formation and maintenance of central water in the North Pacific |
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Authors: | Katsuya Toyama Toshio Suga |
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Institution: | (1) Department of Geophysics, Graduate School of Science, Tohoku University, Sendai Miyagi, 980-8578, Japan;(2) Japan Agency for Marine-Earth Science and Technology, Yokosuka Kanagawa, 237-0061, Japan |
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Abstract: | This study describes the three-dimensional distributions of the Turner angle (Tu) and the potential vorticity (PV) of the
main pycnocline water in the subtropical North Pacific (10–50°N, 120°E–120°W) using a large in situ CTD data set taken by
the Argo profiling floats during June to October of 2001–2009 to clarify the detailed distribution of the central water and
the mode waters as well as the relationship between these water masses. The ventilated part of the main pycnocline water (σ
θ < 26.7 kg m−3) in the subtropical gyre generally displays a sharp peak in Tu value of 59° in the histogram. The Tu histograms for 10° × 10°
geographical boxes mostly show that the mode for the Tu value is 59° too, but they also show some regional differences, suggesting
some types of relations with the North Pacific mode waters. To further investigate this relationship, the appearance probability
density function of the central water (defined as the main pycnocline water with Tu = 56°–63°) and those of the mode waters
with PVs lower than the critical value on each isopycnal surface were analyzed. The distribution area of the central mode
water (CMW) corresponds so well with that of the central water that a direct contribution of the CMW to the formation and
maintenance of the central water is suggested. On the other hand, the distribution areas of subtropical mode water (STMW),
Eastern STMW, and transition region mode water do not correspond to that of the central water. Nevertheless, indirect contributions
of these mode waters to the formation and maintenance of the central water through salt finger type convection or diapycnal
mixing are suggested. |
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