Propagation of semi-diurnal internal tides observed off fukushima,along the east coast of Japan |
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| Authors: | Takeshi Matsuno |
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| Institution: | (1) Faculty of Fisheries, Nagasaki University, 1-14 Bunkyo, 852 Nagasaki |
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| Abstract: | Analysis 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 theM
1 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/offshoreM
2 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. |
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