Transient wind drift currents in a tidal inlet: Theoretical analysis of Ekman drift current and field experiments in Suonada,the Seto Inland Sea |
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| Authors: | Hidekazu Yasuda |
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| Institution: | 1.National Fisheries University,Nagata-Honmachi, Shimonoseki,Japan |
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| Abstract: | Time-dependent wind drift currents in a basin with finite depth have been solved analytically in order to understand their
fundamental behavior in coastal waters. The drift currents due to the land/sea breeze, as a typical example of time-dependent
winds, have been examined with attention to the manner of their oscillation in their vertical profiles. The theoretical analysis
indicates that the drift current due to the land/sea breeze might be amplified effectively around the southern part of Japan,
where the oscillating period of the wind is near to the inertial period. The analysis of the physical process of the drift
current reveals the following two important aspects: the Ekman boundary layer in a rotating frame is physically consistent
with the Stokes boundary layer due to oscillating currents in an inertial frame, and so the inertial motion due to the wind
is dispersed to the deeper level by the vertical viscosity in a rotating frame. The harmonic analysis was performed for the
residual data after removal of the four main tidal constituents, M2, S2, K1 and O1, from the raw data observed in Suonada
sound, the Seto Inland Sea. The feature of the analytically solved drift currents corresponded well to the observed picture.
The vertical viscosity in this field has been estimated at 10−3 m2/s by adjusting the harmonically analytical result of the observed data to the vertical profile of the analytically solved
drift current. |
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