Tidal Harmonic Analysis Results at the Hon Dau Tide Gauge Station

Abstract

The paper presents several results obtained using the tidal harmonic analysis method to analyze annual water level observation data over 51-year period (1960–2011) at the Hon Dau tidal station, Do Son, Hai Phong. The results yield sets of harmonic constants for 13 principal tidal constituents. From the amplitude components of the harmonic constants, it is observed that at the study station, the energy generating tides is dominated by the diurnal tidal group (K₁, O₁, P₁, Q₁) rather than the semidiurnal group (M₂, S₂, N₂, K₂). The shallow-water tidal constituents (M₄, M_S6, and M₆) have relatively small amplitudes compared to the diurnal, semidiurnal, and long-period tidal constituents (semiannual Sa and annual Ssa). The harmonic analysis of one-year data series indicates that the sets of harmonic constants for semidiurnal and diurnal constituents are more stable than those for shallow-water constituents and long-period (Sa and Ssa) constituents. The amplitude components of the harmonic constants for semidiurnal and diurnal tides exhibit anomalous variations with an 18–19 year cycle. This cyclic deviation corresponds to the 18.61-year lunar nodal cycle. It is recommended that when applying tidal harmonic analysis in scientific and technical tasks requiring high accuracy, attention should be given to correcting for the 18.61-year cyclic variation, or alternatively, longer water level observation time series should be used.