| From November 2000 to August 2001, we carried out mooring observations in the region southeast of Okinawa using nine Inverted Echo Sounders with pressure gauges (PIESs) and an upward-looking ADCP. Vertical sections of geostrophic current are calculated from the specific volume anomaly fields estimated by the Gravest Empirical Mode (GEM) method combining the acoustic round-trip travel times between sea bottom and surface with historical hydrographic data. In the upper 500 m layer over the slope shallower than 1000 m depth, the northeastward current increased from a mean of 20 cm/s to 60 cm/s during the occupation of an anticyclonic eddy over the mooring sites, and decreased to -15 cm/s during the occupation of a cyclonic eddy. The 9-month mean geostrophic volume transport relative to the 2000 dbar level between the Okinawa Island and 128.85o E and 25.60 o N was estimated to be 6.1 Sv (1 Sv=10^6 m^3/s) toward northeastward.A nine-year record of the net volume transport from 1992 was estimated through a combined use of the above-mentioned volume transport and sea surface height difference across the observation line. In our presentation, we will show the long period variations of the volume transport such as seasonal and annual cycle. |
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