舟山群岛海域潮波传播变形和不对称性探讨

Discussion on deformation and asymmetry of tide wave propagation in Zhoushan archipelago

舟山海域属于多岛屿海域,潮波受岛屿地形条件影响复杂。根据舟山海域4个潮位站2017年一个月实测逐时潮位以及7个临时测站的大潮、小潮短期逐时潮位资料,采用调和分析及偏度指标计算法,确定了舟山本岛至穿山半岛之间海域的分潮特征及潮汐不对称变化;通过分析浅水潮波方程中的各非线性项,确定了舟山海域浅水分潮产生的主要动力机制;评估了不同频率分潮组合产生的潮汐不对称性贡献值。研究表明,潮波方程中非线性摩擦项是舟山群岛海域浅水分潮变化和潮波变形的主要动力来源;明确了该海域潮汐以M2和S2天文半日潮主导,浅水分潮以M4、MS4分潮为主但潮幅较小,潮波传播过程中耗散潮波能量同时,潮能存在由低频分潮向高频分潮转移,呈现低频天文分潮潮幅沿程减小,高频浅水分潮潮幅增加;潮汐不对称性表现为涨潮占优,大潮期不对称性较小潮期明显,天文半日分潮M2、S2与浅水分潮MS4、M4组合是潮汐不对称性的最大贡献者。

The Zhoushan sea area is a multi-island sea area,and the tidal waves system is complicated for the special topographic conditions of the island.According to the hourly tidal level measured in one month of 2017 at four tidal level stations in Zhoushan sea area and the hourly tidal level data of large and small short term at seven temporary stations,harmonic analysis and skewness index calculation methods were adopted to analyze the tidal characteristics and tidal asymmetrical variation in the sea area between Zhoushan Island and Chuanshan Peninsula.By analyzing the nonlinear terms in the tidal wave equations,the main dynamic mechanisms of the shallow water depth tidal generation in Zhoushan sea were determined.The contribution values of tidal asymmetry generated by different frequency tidal constituent combinations were evaluated.The results show that the nonlinear friction term in the tidal wave equation is the main dynamic source of shallow water depth tidal constitute variations and tidal wave deformation in Zhoushan archipelago.It is obvious that the tides in the area are dominated by M2 and S2 astronomical half-day tides.The tidal ranges of M4 and MS4 are the largest in all shallow water depth tidal contituents although their value are very small.The tidal energy is dissipated during the tidal wave propagation,and the part energy shift from the low-frequency tidal contituents to high-frequency tidal contituents.That is the reason why the tidal wave differences decrease for the low-frequency tidal constitutes but increase for the high-frequency shallow tide.The tidal asymmetry is dominated by flood tide and is lower than during neap tide period.The combination of the astronomical half-day tides M2,S2 and shallow water depth tidal constitutes MS4 and M4 is the main contributor to the tidal asymmetry.