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WHP P2 line was completed through the four separate cruises. The whole observation period extended from October 17, 1993 to November 14, 1994. Of these four cruises, the one that was carried out during the period January 1 to February 10, 1994 had its station coverage of whole P2, although intervals between stations (100 km) were coarser than WHP criterion even in the Kuroshio region. As for other three cruises, intervals between station were close enough. The first of these three cruises covers the eastern two-thirds of P2 and was carried out during October 17 to November 27, 1993. The second covers the central quarter of P2 and was carried out during the period from January 15 to February 4, 1994, and the third was the western quarter during the period from November 2 to November 10, 1994, respectively. P2 coincides with PCM-5 in the Kuroshio region, and another CTD observation was carried out with closer station distibution than WHP criterion during the period from January 15, 1994 to February 4, 1994 along PCM-5. Though there are various ways to make up composite cross-sections using cruises above mentioned to estimate transports across P2, five composites were selected so as not to include apparent inconsistency in the density and the temperature cross-section. Ekman transport was estimated using E-ERS1 wind after taking scalar monthly mean.
The total mass transport across P2 shows the least value of 2 Sv for each composite section when the reference level is set to be 1500 db in the interior region. The northward mass transports integrated from the western boundary takes a maximum value between 45 Sv and 60 Sv around 150°E. Vertically integrated transport from the surface shows two nodes at the depths around 3000 db and 5500 db for three composite sections. The overturning structure in the North Pacific is suggested to be attributed to not only the intrusion of NADW (+LCW) into the bottom layer but also to some other thermohaline processes in upper layer.
Heat transport which is associated with the geostrophic current is always northward taking a value from 0.139 PW to 2.43 PW. On the other hand, the Ekman heat transport changes its direction with season, reflecting the strong seasonal variability of the wind field around 30°N in the North Pacific, and the value changes from -530 TW to +472 TW. Thus, the sum of the geostrophic and the Ekman heat transport gives values from 0.52 PW to 2.86 PW northward and 1.47 PW as the average with a standard error of 1.06 PW. Comparison between this result and other results across 24°N suggests that the North Pacific gains heat from the atomosphere by amounts of 0.7 PW between 24°N and 30°N.
by Masao Fukasawa 1, H. Yoritaka 2, I. Yasuda 3 and S. Imawaki 4
1 Faculty of Oceanography, Tokai University;
2 Hydrographic Department of Maritime Safety Agency;
3 Tohoku Fisheries Laboratory (present: Graduate school, Hokkaido University);
4 Kyushu University
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