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Volume 47 (1991)
- Issue 6 Pages 249-
- Issue 5 Pages 185-
- Issue 4 Pages 105-
- Issue 3 Pages 63-
- Issue 2 Pages 27-
- Issue 1 Pages 1-
Volume 47, Issue 4
Displaying 1-6 of 6 articles from this issue
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Tetsuo Yanagi, Tetsuro Sanuki1991 Volume 47 Issue 4 Pages 105-110
Published: August 25, 1991
Released on J-STAGE: June 17, 2011
JOURNAL FREE ACCESSThe generation, variation, and disappearance of the thermohaline front at the mouth of Tokyo Bay were investigated using water temperature data obtained by a commercial ferry boat in 1987. The thermohaline front was generated south of Kan-non-zaki in mid November 1987 after the beginning of sea-surface cooling. It moved northward to Kan-non-zaki until the end of they ear. The thermohaline front was most intense in February and March and disappeared in late March 1987 when sea-surface warming began.View full abstractDownload PDF (1329K) -
Hong-Ryeol Shin, Yutaka Michida, Yutaka Nagata1991 Volume 47 Issue 4 Pages 111-125
Published: August 25, 1991
Released on J-STAGE: June 17, 2011
JOURNAL FREE ACCESSBy using existing data obtained in the offshore area from the Boso Peninsula to the Joban Coast, it was shown that the double structure of the Kuroshio Front which is usually found along the northern edge of the Kuroshio Extension to the east 143°E (Nagata et al., 1986; Shin et al., 1988)-is hardly found at the edge of the Kuroshio when it is flowing along the Japanese coast or in the area to the west of 142°E. It was suggested that the cold and fresh water core beneath the density front of the double structure originates from the fresh and cold Oyashio Water which is captured beneath the Kuroshio Front just off the Kashima Coast. The double structure of the Kuroshio Front would be generated and developed very rapidly in the region between 142°E and 143°E just after the Kuroshio leaves the Japanese coast.View full abstractDownload PDF (2106K) -
Shigenobu Takeda, Yoshihachiro Nimura, Reijiro Hirano1991 Volume 47 Issue 4 Pages 126-137
Published: August 25, 1991
Released on J-STAGE: June 17, 2011
JOURNAL FREE ACCESSAoshio-hypoxic water which can be distinguished from surrounding coastal water by its milky blue-green color-is often observed at the head of Tokyo Bay when coastal upwelling of sulfidic bottom water occurs during summer and early autumn. Optical properties and the biological-chemical composition of suspended matter in the aoshio water were investigated using nearby “normal” coastal water as a reference.
Suspended matter in the aoshio water contributed to the large beam-attenuation coefficient and also to the strong upward radiance with maximal intensity around 550 nm as a result of the scattering process. No significant difference in bacterial density was observed between samples of aoshio water and reference coastal water. The low chlorophylls concentration in aoshio water samples indicates that biological pigments may not play a dominant role in the color of the aoshio events.
The suspended particles in aoshio water samples had much higher contents of sulfur and manganese and a lower silicon content than those in reference coastal water samples. The colloidal elemental sulfur and manganese-rich particles identified in the aoshio water appear to be oxidation products of dissolved sulfide and manganese (II) in the anoxic water.
On the basis of these findings, it may be concluded that there is a high probability that elemental sulfur and manganese-rich particles are responsible for the color and turbidity in aoshio.View full abstractDownload PDF (6191K) -
Takeshi Matsuno1991 Volume 47 Issue 4 Pages 138-151
Published: August 25, 1991
Released on J-STAGE: June 17, 2011
JOURNAL FREE ACCESSAnalysis of current velocity and temperature records obtained from moored buoy systems deployed off the east coast of Japan reveals the intermittent occurrence of semi-diurnal internal tides and their manner of propagation. The internal tidal waves clearly propagate toward the shore, which is confirmed by cross-correlation of the onshore current velocity and temperature between neighboring stations. The propagation speed of the internal tide increases with water depth except in the area furthest offshore. In this area, motions near the second mode seem to occur occasionally, while in the nearshore area the motions for the most part consist of the first mode.
Through harmonic analysis, it is shown that the M2 internal motions were not vertically homogeneous. That is, the internal motions are greater at the lower level in the nearshore area while they are greater at the upper level in the offshore area. Pathways along which the energy of the internal tide should propagate are estimated in such a way that the characteristic curves pass through the area over which relatively large onshore/offshore M2 velocity is distributed. The movement of the characteristic ray of a certain phase explains the observed phase velocity estimated from the cross-correlation diagrams. Internal motions around the characteristic ray were pronounced in a rather wide area. Thus, it is suggested that the generation region of the internal tide in the present study area might be relatively wide.View full abstractDownload PDF (2061K) -
Masaaki Wakatsuchi, Seelye Martin1991 Volume 47 Issue 4 Pages 152-168
Published: August 25, 1991
Released on J-STAGE: June 17, 2011
JOURNAL FREE ACCESSThis paper describes the water circulation in the Kuril Basin and its role in the formation and seasonal variation in intensity of the large anticyclonic eddies which occur in the basin. Oceanographic data for the period June 1977 through June 1979 suggest that these eddies develop in summer and decay in winter. In summer, the eddy development is associated with a deepening of the isopycnals caused by the surface flow of the Soya Warm Current over the basin, and the deep advection of cold, less saline, oxygen-rich water from Terpenia Bay and the eastern continental shelf of Sakhalin Island. In winter, the eddy decay is caused by surface cooling and convective mixing downward of the warm, saline surface water, which causes the isopycnals to rise and leads to an attenuation of the eddies. This combination of the summer influx of water into the region, and the fall and winter cooling of the eddies leads to the annual variation in eddy intensity.View full abstractDownload PDF (2344K) -
Lecture by the Member Awarded the Okada Prize of the Oceanographical Society of Japan for 1991Kazunori Akitomo1991 Volume 47 Issue 4 Pages 169-183
Published: August 25, 1991
Released on J-STAGE: June 17, 2011
JOURNAL FREE ACCESSThe author reviews his study on generation mechanism of a shallow sea front and its variabilities awarded the Okada Prize of the Oceanographical Society of Japan for 1991.
A new physical model is proposed for frontogenesis (nonhydrostatic model) in a shallow sea such as the Kii Channel during winter. This model retains the vertical acceleration term in momentum equation to simulate properly phenomena of a large aspect-ratio in the frontal region, such as gravitational convection induced by surface cooling.
Numerical experiments are carried out to examine the validity of the model by using vertically two-dimensional model basin. Gravitational convection induced in the frontal region strengthens the horizontal convergence to form a remarkable front comparable to the observed one and that this effect of convection surpasses that of a tenfold cooling rate in a usual model adopting the hydrostatic approximation. It is also found that sharpness of front largely depends on horizontal eddy viscosity (diffusivity).
Water exchange process caused by fluctuations of front is examined by tracking numerous labeled particles. Gravitational convection also plays an important role in this process by producing a large Lagrangian drift in the frontal region.View full abstractDownload PDF (7265K)
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