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Abstract:
The lunar nodal cycle, causing by moon’s declination variations over the period of 18.61 years, results in changes in the amplitude and phase lags of global tidal constituents. However, the observed range in tidal amplitude is at present not yet well understood, and it is crucial for coastal hazard planning and chart datum. The impact of the nodal tide including its plausibly varying amplitudes and phase changes on the highest astronomical tide along the Northwest Pacific coast in North American could be important as a scientific basis for future coastal disaster planning. Additionally, there is no standard procedure of computing the lowest 18.61-year astronomical tides. Hence, we analyzed the contributions of various factors for calculating the lowest astronomical tide, including time spans, sampling frequencies, number of tidal constituents, and nodal tide correction, and establish a standard procedure which was adopted in Taiwan. Finally, we use a modified two-step harmonic analysis procedure to re-evaluate the seasonality and slope variability of the major constitutes (M2, S2, K2, and O1) along the Pacific Northwest coast in North Ametrica, and analyze the difference between the observed nodal amplitudes and the values predicted by equilibrium tidal theory.
