Tidal and residual currents in the Qiongzhou Strait estimated from shipboard ADCP data using a modified tidal harmonic analysis method

Abstract

In spring 2013, 33 repeat shipboard Acoustic Doppler Current Profile (ADCP) surveys were conducted to measure the tidal current in the Qiongzhou Strait (QS). The major tidal currents and the residual current along a section across the QS were estimated using a modified tidal harmonic analysis method based on the inverse technique. A simple simulation and comparisons with previous observations demonstrated that the tidal currents estimated using the modified tidal harmonic analysis method are reasonable, and this method was able to control the magnitude and deviation of the estimation error. The direction of the major axis of tidal current ellipses is generally along the strait. Diurnal tidal constituents are dominant among the five tidal current constituents (K1, O1, M2, S2, and MSf). The ratio of the amplitudes of O1, K1, M2, S2, and MSf, averaged along the section across the QS is 1:0.79:0.42:0.27:0.29. The residual current along the entire section is all westward; the averaged velocity over the section is 6.0±2.1 cm s-1; the associated volume transport through the section is -0.065±0.046 Sv (Sv=106 × m3 s-1), in which the second value denotes the uncertainty of first value. Dynamic analysis indicates that tidal current activity is more dominant than mean current and eddy activity, and tidal rectification and sea level difference between two entrances of the QS are important in maintaining the residual current through the strait.