内孤立波过陆架陆坡地形的数值模拟研究

Numerical investigation of the evolution of internal solitary waves over shelf-slope topography

内波是海洋中普遍存在的波动形式。内孤立波是典型的非线性内波,多发于陆架边缘海,如南海等海域,对陆架海域有重要影响。本文针对内孤立波在陆架地形上的传播问题,先基于弱非线性与全非线性数值模型,模拟了不同振幅、地形高度条件下内孤立波的演化的过程,探讨了动力系数对内孤立波演化过程的影响,对比了两模型的模拟结果在内孤立波演化过程、能量分配以及能量耗散的差异,后分析了南海的动力系数分布特征。结果表明,在内孤立波不发生破碎的情况下,弱非线性模型与全非线性模拟结果相近。当发生破碎过程时,弱非线性模型可准确模拟头波,但无法通过强非线性的破碎过程耗散能量,只能以裂变的方式辐射能量。在弱非线性模型中,随地形高度增加,频散系数减小到零,平方非线性系数由负转正,立方非线性系数绝对值增大一个量级,并主导陆架地形上内孤立波的演化过程。通过对比南海夏季与冬季非线性内波动力系数空间分布,发现内孤立波在传播过程由于夏季平方非线性效应、立方非线性效应与频散效应较强的影响,其在夏季更易发生陡化与裂变,波列发生频率高。

Internal waves are ubiquitous ocean waveforms,in which internal solitary waves(ISWs)are typical nonlinear internal waves.Marginal seas are hotspots for ISWs in the ocean,such as the South China Sea(SCS),where the evolution of ISWs is of great importance.Based on weakly and fully nonlinear numerical models,the evolution and dynamics of ISWs over shelf-slope topography under different incident amplitudes and topography heights are investigated.The effects of kinematic parameters,differences in evolution and energy between the two models,and the distribution of kinematic parameters in the SCS are analyzed.The results show that the simulations of the weakly nonlinear model agree well with those of the fully nonlinear model in the non-break case.As the breaking occurs,the weakly nonlinear model can simulate the leading wave well,but it shows a deficiency in energy dissipation and breaking as fission dissipates energy.The dispersion parameter decreases to 0,the quadratic nonlinear parameter changes sign,and the value of the cubic nonlinear parameter increases by an order of magnitude,indicating that the effects of the quadratic nonlinear parameter and dispersion are weak and the effect of the cubic nonlinear parameter dominates the evolution over shelf-slope topography.The spatial distribution of kinematic parameters in the South China Sea shows that ISWs are more likely to steepen and fission and more likely to develop into a wave train in summer。