Computation methods of major tidal currents from satellite-tracked drifter positions, with application to the Yellow and East China Seas

Abstract

[1] Two practical techniques of "correction method'' and "fitting method'' for computing major diurnal and semidiurnal tidal currents from irregular satellite-tracked drifter position data have been developed and then applied to the Yellow and East China Seas to compute M(2) and K(1) currents. The correction method calculates the most dominant diurnal and semidiurnal tidal currents using the correction coefficients, defined amplitude ratios, and phase differences between the major tidal currents. On the other hand, the fitting method calculates major tidal currents by fitting the amplitudes and phases to a given polynomial function in space, without utilization of the correction coefficients. Validation tests for sampling intervals, data truncation, effects of low-frequency currents, and position errors are performed to improve computation results. Both methods enable us to evaluate effectively and correctly strong tidal currents provided that the signal-to-noise level in drifter positions is not significantly high. The spatial pattern and current ellipses of M(2) and K(1) tidal currents from drifter positions in the Yellow Sea are fairly well consistent with those from moored current data. Application of the two methods to the Yellow and East China Seas exhibits commonly that M(2) and K(1) currents rotate clockwise in the East China Sea but counterclockwise in the Yellow Sea interior, with rotation direction change around 35degrees and 34degrees N, respectively.