南海北部陆架区内波的演变与耗散机制

海洋是多尺度强迫-耗散系统，机械能主要在大尺度输入，在小尺度耗散。在大、中尺度运动的能量向小尺度湍流传递过程中，内波扮演着重要角色。内波的生成和破碎可打破海洋动力平衡，而在陆架区，内波（主要是内孤立波）的浅化演变与耗散则是驱动湍流混合的关键过程。通过长期的理论、观测与数值模拟研究，目前已认识到内波浅化过程中主要发生如下演变：波形调制、极性转变、裂变、破碎与耗散。相较于直接发生破碎，浅化演变过程中的裂变及其引发的剪切不稳定和对流不稳定是内孤立波在陆架区的主要耗散机制，显著调制陆架区的跃层混合。从能量串级的角度讲，内孤立波浅化裂变为动力不稳定的高频内波是潮能串级的重要通道。本文简要回顾南海北部陆架区内波的研究历史，并着重总结内波在陆架区演变与耗散机制的研究进展。

Evolution and Dissipation Mechanisms of Shoaling Internal Waves on the Northern Continental Shelf of the South China Sea

The ocean is a multiscale forced-dissipative system where mechanical energy is input mainly at large scales and dissipated at small scales. Internal wave is the key process of energy cascade from large-scale and mesoscale motions to small-scale turbulence. The generation and dissipation of internal waves can break the dynamic equilibrium of oceanic flows and is an important pathway of ocean energy cascade. The evolution and dissipation of shoaling internal waves (especially internal solitary waves) on the continental shelf is a key mechanism driving offshore mixing. Recent decades of theoretical, observational and numerical studies revealed the critical evolution processes of the shoaling internal waves: wave deformation, polarity conversion, fission, breaking and dissipation. Compared with direct breaking, fission and its accompanying shear instability and convective instability are the main mechanisms of wave dissipation on the continental shelf and result in significant ocean mixing. From the viewpoint of energy cascade, fission of shoaling internal solitary waves into high-frequency waves is an important pathway of tidal energy cascade. Here we briefly review studies of internal waves on the northern continental shelf of the South China Sea, and highlight in particular recent advances in the study of the evolution and dissipation mechanisms of shoaling internal waves.