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MODEL RESULTS
 
Tidal computation of the Ariake Sea
 
The model was integrated for 12 tidal periods (six days in M2 constituent). The model results are shown in Figure 3 from the final period. The amplitude and phase of the tidal elevation were calculated by the harmonic decomposition from the elevation results of each constituent case run. Figure 3 is the co-amplitude and the co-phase tidal chart of the M2 constituent. Tidal harmonic constants at nine stations (Sasebo, Nakura, Hukahori, Matugae, Aba, Akune, Kutinotu, Takezaki Sima and Yatsusiro) from the table of the tidal harmonic constant published by the Japan Coast Guard were compared with computed data (Table 1, Fig.4). The RMS (root mean square error) of the amplitude was 9.249 cm, and the RMS of phase is 3.838 degrees. The result of tidal computation shows the similar result with observed data, but the over-amplitude in inner bay of the Ariake Sea estimated. It seems that this model cannot estimate the variable tideland topography clearly.
 
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Figure 3. The amplitude (in unit of cm) and the phase (in unit of degree referred Greenwich) of the M2 tidal chart computed by the model
 
Table 1. Observed and computed tide data of M2 constituent
Location Observed amplitude (cm) Observed phase (degree) Computed amplitude (cm) Computed phase (degree)
Sasebo 85.0 340.043 84.592 341.255
Nakura 68.6 347.743 65.441 348.904
Aba 94.9 333.143 93.098 334.724
Matugae 83.5 328.943 84.417 331.579
Hukahori 83.8 329.543 83.525 330.939
Takezaki Sima 155.1 358.343 180.025 5.864
Kutinotu 101.4 350.143 107.680 356.000
Yatsusiro 112.4 351.843 122.112 357.085
Akune 79.7 320.243 80.406 320.224
 
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Figure 4. The comparison chart between observed and computed M2 tidal constituent
 
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Figure 5. The computed tidal ellipses chart at the surface layer of M2 constituent
 
Figure 5 shows the surface tidal current of M2 constituent. The mouth of the Ariake Sea shows strong current, and the current of the inner Ariake Sea shows the strong currents at 3 hr and 9 hr (lunar time) and clockwise current pattern.
 
The mean current vectors averaged over one tidal period are shown in Figure 6. There are two strong mean current pattern; one is a northwestward current in inner Ariake Sea by anticyclonic eddies on the onshore side, and the other is a southward flow near the eastern boundary. The southward mean flow over the eastern coastline was recently suggested from the results of the drifter track observations made in July 1992. Figure 7 shows the mean flow pattern inferred from this observation undertook by Ariake Fishery Institute and Sanyo Techno Marin Inc. From Figure 7 we can see a northwestward flow in the offshore region and a southward flow along the east coast. These features agree well with that in Figure 6. The similar result is shown in the study of inner Ariake Bay (Hukuda et al., 1994).
 
Figure 6. The depth-averaged residual current vectors
 
Figure 7. The surface mean current pattern inferred from the results of drifter track observations made in July 1992. Cited from "A report on tidal analysis in Ariake Kai fishing grounds" by Sanyo Techno Marine Inc. (1993)







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