Seasonal variation of the main tidal constituents in the Bohai Bay

Abstract

Abstract. The seasonal variability of the M2 tidal amplitude has been observed widely, especially in the coastal regions, but the seasonal variations in several major tidal constituents have not been investigated sufficiently. In this study, the seasonal variations in the major tidal constituents, including M2, S2, K1, and O1, in the Bohai Bay, China, are studied by analysing one-year observations of the sea level at two stations, E1 and E2. At E2, the frequencies of the M2 tidal amplitude and phase are annual, with large values in summer and small values in winter, while the frequencies of the S2 and K1 tidal amplitudes are semi-annual. Furthermore, the O1 tidal amplitude increases constantly from winter to autumn. The maxima of the phases appear twice in one year for the S2, K1, and O1 tides, which take place nearly in winter and summer. The seasonally varying trends at E1 estimated by the enhanced harmonic analysis are similar to those at E2, except for the O1 tidal amplitude. The results of the numerical experiments indicate that the seasonality of the stratification and the corresponding vertical eddy viscosity coefficient induce seasonal variations in the phases and amplitudes for all the major tidal constituents, respectively.