台湾岛东北海域潮致内孤立波二维数值模拟

2-D Numerical Simulation of Internal Solitary Waves in the Sea Waters to the Northeast of Taiwan Island

现场观测和卫星遥感SAR图片均表明,台湾岛东北海域存在大量复杂的、无规则的内孤立波(列)。本文采用完全非线性非静力平衡的MITgcm模式,分别采用M2和K1分潮驱动,对该海域内孤立波的生成过程及其机制进行了二维数值模拟研究。研究揭示,该海域的内孤立波主要源于附近2个海槛处的潮地相互作用。正压潮流流经海脊时会激发内孤立波,潮流由退潮转换为涨潮时激发西向传播的内孤立波,由涨潮转换为退潮时则激发东向传播的内孤立波。通过对潮汐偏移及地形弗鲁德数的分析表明,内孤立波的产生机制是混合山后波机制。在海槛西侧,内孤立波在涨潮时向西传播,在落潮时受背景潮流的限制,西传速度明显减慢,甚至停滞;在海槛东侧,存在东传的第二模态内孤立波,并最终在向深海传播过程中逐渐消亡。本文设计了6个敏感性试验,以考察不同因子对内孤立波的生成和传播过程的影响。不同分潮驱动的数值实验表明,此区域的内孤立波主要是由半日分潮M2引起的,由于靠近全日分潮的临界纬度,单独的K1分潮不激发内孤立波。其他敏感性实验显示,海水层化对内孤立波的生成和传播有较大影响;科氏力对内孤立波的传播速度有一定的影响。

Rank-ordered packets of nonlinear internal solitary waves （ISWs） in the northeast of Taiwan are often observed in the SAR images and they are quite complicated.A 2-D fully nonlinear non-hydrostatic model,MITgcm,with M2 tidal forcing and a simplified topography is applied to investigate the generation process and mechanism of the ISWs there.Tidal-topography interaction plays an important role in the generation and the propagate process of the ISWs in this region.Modeling results show that the internal waves are generated when the barotropic current flows over two sills.Analysis of tidal excursion and the topographic Froude number,which govern the generation process indicates that the generation of internal waves in this area is subject to mixed lee wave mechanism.On the left side that close to the continental,ISWs are generated when the tidal flow on the sill-top changes from ebb to flood tides,which move westward in the ebb tides while they are trapped in the flood tides.On the right side that away from the continental,second mode ISWs are generated and develop into a series of ISWs with the amplitude declining during its propagating to the deep ocean.Sensitive numerical experiments with different influencing factors are taken to investigate the generation and propagation mechanisms of the ISWs.It is revealed that the internal solitary waves in this area are excited by semi-diurnal M2 tide,while the K1 tidal alone can not generate ISWs with large amplitude as the study region is close to its critical latitude.The results also show that the stratification and Coriolis force have influences on the generation and propagation of ISWs while the effect of horizontal model resolution are negligible to low mode ISWs.