Kazuo Kawatate

Cross-stream survey of the upper 400 m of the Kuroshio by an ADCP on a towed fish

A section across the Kuroshio and the adjacent area on the East China Sea shelf was measured by an Acoustic Doppler Current Profiler (ADCP) mounted on a towed fish. The section covered the upper 400 m with a horizontal interval of 200 m and a depth interval of 8 m. The measured vertical profiles made it possible to construct a detailed contour plot of velocity in this section. The calculated volume transport of the Kuroshio through this section and extrapolated to 700 m depth was 27.2 Sv (1 Sv = 1×106m3s−1), 30–40% higher than estimated by geostrophy with a level of no motion of 700 db.

Measurements of east Tushima Current in winter and estimation of its seasonal variability

AbstractThe Tushima Current in the east channel was measured in a site of the strong current between Tushima and Iki Islands for 43 days of the winter in 1986. The primary results are:First, it was highly barotropic and flowed northeastward with a mean speed of about 20 cm sec−1. Second, it was decelerated by northeast winds rather than by northwest winds in a frequency range of 0.3 and 0.4 cpd. Third, the scale analysis showed that the Tushima Current is approximately in geostrophic balance. The best empirical relationship between the measured Tushima Current and cross-channel adjusted sea level difference is given by

A report on failures of current meter moorings set east of Tsushima Island from 1983 to 1987

V = 3.0(\Delta \eta _{K - I} - 65.5cm),

Self-governing profiling system

whereV (cm sec−1) andΔηK−I (cm) denote the northeast current component and the adjusted sea level difference between the average of three tidal stations (Moji, Hakata, and Sasebo) and Izuhara. Finally, the annual variation of the Tushima Current estimated from coastal sea level data during the past 19 years using the above formula showed a much weaker seasonal change in the east strait than in the Korea Strait.

A note on internal wavetrains and the associated undulation of the sea surface observed upstream of seamounts

In each of the (fiscal) years 1979–1982, multilayer current measurements by means of moored instruments were carried out in the Kuroshio off Tanegashima Island, south of Kyushu, with particular interest in the baroclinic layer (0–1,000 m) of the intense current. Most of the moored instruments were in position for more than 30 days, the maximum duration being 145 days. This paper describes some noticeable features of the mean and fluctuation fields in the surface Kuroshio as inferred from the the new data sets.Vertical profiles of horizontal velocities show that the eastward current of the Kuroshio in the region is confined to the upper 600 m on average and below this level the mean current is directed to the southwest along the local isobaths. This is believed to be the first observation of the “level of no motion” in this region. It is argued that the indicated level of no motion would lead to much smaller values for the Kuroshio transport than previous values referred to the 1,000 m level — for example, earlier estimates by Nitani (1972).The fluctuation field in the upper intense current appears to be dominated by an organized motion with a time scale of about 30 days. This can be seen clearly in the time variations of water temperature and local volume transport, but less clearly in the velocity records. The horizontal transfer components of momentum and heat are calculated and it is suggested that the transverse momentum transfer, U′V′ tends to be negative (offshore) in the region of anticyclonic shear of the upper Kuroshio; no evidence for a “negative eddy viscosity effect” is found.

A cross-spectral analysis of small voltage variation in a submarine cable between Hamada and Pusan with speed variation of the Tsushima warm current

Abstract On the basis of field records, we describe failures of current meter moorings deployed in the Tsushima Strait from 1983 to 1987. In order to avoid future failures of current meter moorings, we should communicate frequently with the fishermens union and deploy the moorings with reserve flotation and acoustic release.

A dynamic two-dimensional calculation of underwater lines

Abstract Data on the Tsushima Current and its neighboring coastal current are analyzed to examine short-term variability of the currents and storm events due to typhoons. A three current-meter array was deployed in a strong current region of the east Tsushima channel during summer in 1983 and 1984, and other two current-meter arrays in the eastern coastal area of the channel (the Sea of Genkai) in the summer and autumn in 1983. The observations of coastal current show that the kinetic energy of the subtidal current component was larger in summer than in autumn by a factor of about 2. A comparison of the wind stresses and the estimated values of mixed layer depth in the summer and autumn season suggest that this seasonal change is closely associated with that of the mixed layer depth rather than with that of the wind stress. The Tsushima Current was greatly influenced by two storm events: its speed increased by a factor of 2 in one event and decreased to nearly zero in the other. Such a large variation of mean current during the storm was observed only for the Tsushima Current and not for the coastal current, suggesting that the Tsushima Current may temporarily change its regular course as a result of a storm.

A Simple Dynamic Calculation of Launching a Line

Abstract A self-governing profiling system with a depth capability of 100 m has been developed for measuring flow velocity, temperature, salinity, and turbidity of water in the near-bottom parts of shelf seas. In the system, a moving profiler unit holding the sensors for measuring the above parameters and depth and containing a data-recording device is made to move up and down, in cycles, along a mooring line. This motion of the profiler unit is governed by a self-contained microprocessor. The system has been field-tested: examples of recorded data are presented.