M2 Tidal Current Estimation from One-day Observation Data off the Western and Southern Coasts of Korea
A practical method to estimate the M2 tidal current is proposed based on one-day current observations. In this method, the semi-diurnal constituent, composed of several constituents within the semi-diurnal frequency band that cannot be resolved from one-day observations, is corrected to the M2 constituent using the amplitude ratio and phase difference between each constituent. The dominant M2 constituent is accurately estimated from the semi-diurnal constituents. However, this method is not always successful for application to diurnal constituents that are much weaker than the M2 constituent. The accuracy of the method depends on the signal-to-noise ratio and the time of observation. Observations conducted during the spring tide period are highly recommended to reduce calculation error. This method was applied along the western and southern coasts of Korea, where the semi-diurnal tidal current is the most predominant component of water circulation. In this study, six major constituents (M2, S2, N2, K2, O2, and 2N2) that are dominant in the semi-diurnal frequency are used for correction of the M2 tidal current. Correction coefficients for S2 and N2 used were the average values from 122 sets of one-month current observations, which have a relatively uniform spatial distribution in the study area. For correction coefficients of K2, v2, and 2N2, we used wellknown constant values determined from the relationships among astronomical forcing factors. The M2 tidal currents after correction are generally well matched to those calculated with the numerical model. The discrepancy between results is mainly due to the complex bathymetry and coastline in the study area, which cannot be fully resolved with a numerical model. A spatial distribution map of the M2 tidal current based on observations in this area is presented for the first time. The method proposed in this study can be used for planning efficient observation of tidal currents.