Tidal currents and Kuroshio transport variations in the Tokara Strait estimated from ferryboat ADCP data
2017
Zhu, Xiao‐Hua | Nakamura, Hirohiko | Dong, Menghong | Nishina, Ayako | Yamashiro, Toru
From 2003 to 2011, current surveys, using an acoustic Doppler current profiler (ADCP) mounted on the Ferry Naminoue, were conducted across the Tokara Strait (TkS). Resulting velocity sections (1234) were used to estimate major tidal current constituents in the TkS. The semidiurnal M₂ tidal current (maximum amplitude 27 cm s⁻¹) was dominant among all the tidal constituents, and the diurnal K₁ tidal current (maximum amplitude 21 cm s⁻¹) was the largest among all the diurnal tidal constituents. Over the section, the ratios, relative to M₂, of averaged amplitudes of M₂, S₂, N₂, K₂, K₁, O₁, P₁, and Q₁ tidal currents were 1.00:0.44:0.21:0.12:0.56:0.33:0.14:0.10. Tidal currents estimated from the ship‐mounted ADCP data were in good agreement with those from the mooring ADCP data. Their root‐mean‐square difference for the M₂ tidal current amplitude was 2.0 cm s⁻¹. After removing the tidal currents, the annual‐mean of the net volume transport (NVT) through the TkS ± its standard derivation was 23.03 ± 3.31 Sv (Sv = 10⁶ m³ s⁻¹). The maximum (minimum) monthly mean NVT occurred in July (November) with 24.60 (21.47) Sv. NVT values from the ship‐mounted ADCP were in good agreement with previous geostrophic volume transports calculated from conductivity temperature depth data, but the former showed much finer temporal structure than those from the geostrophic calculation.
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