渤海湾M2分潮的季节变化:增强调和分析的应用

M₂分潮的季节变化对沿海的海洋环境有着重要影响。增强调和分析(EHA)既可以提取主要分潮时变的振幅和迟角，同时可以得到其他分潮不随时间变化的振幅和迟角。本文利用EHA分析渤海湾两个站点的水位数据，研究了渤海湾M₂分潮的季节变化。为了评估EHA方法的准确性，在理想实验中设计了人造“水位数据”。利用EHA分析得到的M₂分潮时变振幅和迟角以及S₂、K₁、O₁分潮不随时间变化的振幅和迟角均比其他方法得到的结果更接近给定值，表明了EHA的有效性和可用性。当使用EHA分析渤海湾实际海平面观测数据时，得到的M₂分潮振幅具有明显的季节变化特征:夏季较大，冬季较小。敏感性实验表明，分析所得渤海湾M₂分潮振幅的季节变化趋势不受实验设置的影响，是鲁棒的，能够反映该海域真实的M₂分潮季节变化。此外，渤海湾M₂分潮振幅的季节变化可能是东亚季风通过影响平均海平面、层化和涡动黏性系数的季节变化而引起的。

Seasonal variability of the M2 constituent in the Bohai Bay: Application of enhanced harmonic analysis

The seasonal variability of M₂ constituent exerts a major influence on the coastal ocean environment. The enhanced harmonic analysis (EHA) can synchronously extract the temporally varying amplitudes and phase lags of significant constituent and the constant values of the other constituents. In this study, the seasonal variability of the M₂ constituent in the Bohai Bay, China, is investigated by analyzing one-year sea level observations at two stations with EHA. In order to evaluate the accuracy of EHA, artificial "sea level" is designed in the ideal experiment. Both the estimated temporally varying amplitude and phase lag of the M₂ constituent and constant values of the S₂, K₁ and O₁ constituents using EHA were much closer to the prescribed values than those obtained using the other methods, indicating the capability and efficacy of EHA. When the real sea level observations were analyzed using EHA, the estimated M₂ constituent amplitude has significant seasonal variability, with large values in summer and small values in winter. The sensitivity experiments show that the trend of seasonal variation of M₂ amplitude in Bohai Bay is not affected by the experimental settings, and it is robust and can reflect the real seasonal variation of M₂ constituent. The seasonal variations in the M₂ amplitude is possibly induced by the seasonally alternating Asia monsoon, as the Asia monsoon dominates the seasonality of mean sea level, stratification and eddy viscosity, which are main influence factors summarized in the previous studies.