| Tidal hydrodynamics is of great importance to coastal fisheries and marineecosystem studies. A Beibu Gulf tidal model was established based on the FiniteVolume Community Ocean Model (FVCOM). Tidal information for the study areawas extracted from about6.5year Jason-1satellite altimeter data and wasassimilated into the model using Nudging method.Predicted elevation was applied as open boundary conditions by using itsharmonic constants of six constituents (S2，M2，N2，K1，O1，Q1) from China Seaand local Tidal Solution in OTIS (OSU Tidal Data Inversion). This paper usedthree schemes to establish Beibu Gulf tidal model. They are:1) Simply using openboundary condition to drive the model, and the coefficient of bottom roughnesswas0.0015.2) Based on scheme1, assimilating the model using Nudging methodwith satellite altimeter data.3) Also based on scheme1, optimizing the openboundary conditions and setting the bottom as a roughness spatially distributedfield.By the results of the scheme2and scheme1, the assimilation of altimeter dataimproved the accuracy of model results. Average error of m1tide amplitudereduced from24.73cm to5.91cm and that of phase-lag reduced from14.76°to11.11°, while average error for M2tide amplitude reduced from7.96cm to7.57cm and that of phase-lag reduced from34.33°to7.21°. Although significantimprovement was made, the accuracy was not ideal compared with gauges data. By the results of the scheme3and scheme1, it can be found that optimizingthe open boundary conditions and setting a bottom roughness spatially distributedfield also improved the accuracy of model results. Average error for m1tideamplitude reduced from24.73cm to2.74cm and that of phase-lag reduced from14.76°to5.40°, while average error for M2tide amplitude reduced from7.96cmto6.19cm and that of phase-lag reduced from34.33°to7.24°. Compared with thescheme2, scheme3obtained more desirable results, and simulated the moresignificant aspect of the local characteristic of the tidal field.Probably because Beibu Gulf is a gulf with shallow water, the measurementaccuracy by the Jason-1altimeter is also questionable. In addition, thediscontinuity of the altimeter data adjacent to the islands may also affect thealtimeter data accuracy. While the study area is small and that the spatial resolutionof the satellite data is low. Relatively large sampling interval of altimeter is likelyto cause high frequency aliasing of the tidal signal.In this paper the m1and M2tides and tidal currents characteristics areanalyzed in detail. Both results of scheme2and scheme3have basic agreementwith previous studies. Model results indicate that Beibu Gulf features standarddiurnal tidal characters. Amplitude of m1is minimum at the southwest part of thestudy area and peaks at the northmost tip. A degenerate amphidromic point for m1is located along the coast of Hue around which the co-tidal lines rotatecounterclockwisely. Amplitude of M2is much smaller than that of m1. A degenerateamphidromic point for M2is located north of Haiphong around which the co-tidallines rotate counterclockwisely. Tidal currents is similar to tides in Beibu Gulf inthe sense that m1constituent is dominant. Velocities of m1tidal currents are muchhigher than that of M2off the west and northwest coast of Hainan Island. Majoraxes of m1and M2currents are east-west within the Qiongzhou Strait while theothers are generally along the axis of the gulf. For both m1and M2tides, their currents are mostly rectilinear but are strongly of rotation off the both openings ofthe Qiongzhou Strait. In addition, m1current in the mouth of Gulf that is south toHainan Island, as well as M2current inside of the Gulf that is west to the Island, isof highly rotation. |
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