Seasonal variation of the main tidal constituents in the Bohai Bay

Abstract. The seasonal variability of the M 2 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 M 2 , S 2 , K 1 , and O 1 , 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 M 2 tidal amplitude and phase are annual, with large values in summer and small values in winter, while the frequencies of the S 2 and K 1 tidal amplitudes are semi-annual. Furthermore, the O 1 tidal amplitude increases constantly from winter to autumn. The maxima of the phases appear twice in one year for the S 2 , K 1 , and O 1 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 O 1 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.