In order to estimate the variability of current structure and mean geostrophic volume transport in the southeast of Okinawa Island, the round‐trip acoustic travel times between sea bottom and surface at nine sites were measured by Inverted Echo Sounder with pressure gauge (PIES) from November 2000 to August 2001. Vertical sections of geostrophic velocity are calculated by using vertical profiles of specific volume anomaly derived by the Gravest Empirical Mode method from the PIES data. In the upper 500 m layer over a slope shallower than 1000 m depth, the northeastward current reached up to 60 cm s−1 during the occupation of an anticyclonic eddy, and decreased to −15 cm s−1 during the occupation of a cyclonic eddy, around the mean of 20 cm s−1. The temporal mean geostrophic volume transport relative to the 2000 dbar level was estimated to be 6.1 Sv (1 Sv ≡ 106 m3 s−1) northeastward in the west of 128.85°E.
The steady streaming induced by oscillatory viscous flow of small amplitudes over a wavy wall has been analysed, and the computed flow patterns have been found to agree well with the flow patterns visualized experimentally in a tube. When the first parameter, α/δ (the ratio of the wavelength of the wavy wall to the thickness of Stokes layer), becomes larger than about 26, the streaming has a double structure consisting of regions of upper and lower pairs of recirculations. As the second parameter, L/δ (the ratio of the amplitude of the wavy wall to the thickness of Stokes layer), is increased, the upper pair of recirculations squeezes in a gap between the lower recirculations above the troughs of the wall. A similar double structure of steady streamings was also observed above ripple marks formed under oscillatory viscous flow. A bearing is suggested of this phenomenon on the determination of stationary profiles of ripple marks.
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