內波在海洋表面顯露形跡之調變解析

Theoretical Modulation of Internal Wave Exposure on the Sea Surface

黃煌煇(Hwung-Hweng Hwung) ； 楊瑞源(Ray-Yeng Yang) ； 伊格爾．休爾干(Igor V. Shugan)

《海洋工程學刊》 12卷1期 (2012/06) Pp. 61-74

https://doi.org/10.6266/JCOE.2012.1201.03

摘要

本研究係以理論解析方式探討由內波引致海洋表面下層流 （subsurface current）對於弱非線性史托克斯表面波（Stokes surface wave）之衝擊影響。由調變方程式（modulation equation）的理論解析解可求得在接近群波速度的共振現象（group velocity resonance），分析結果顯示平靜的下游表面波將伴隨相對高頻率的調變，而表面波的包絡線則會生成一反向流的輪廓；此為海洋內波在海水表面產生蹤跡的可能性，為一種表面波列調變生成的出現。在此條件下表面長波會在內波之前形成波動調變先兆，而相對較短之表面波則會引致內波的蹤跡。經由週期內波波列引發之表面波調變，其特徵週期則短於內波之週期；但由內波所激發之表面波則僅於反向流中具足夠充分之群共振時才有可能被發現。

關鍵字

史托克斯表面波 ； 內波 ； 表面下層流 ； 調變方程式

並列摘要

The impact of subsurface currents induced by internal waves (IW) on nonlinear Stokes surface waves (SW) is theoretically analyzed. An analytical and numerical solution of the modulation equations are found under the conditions close to the group velocity resonance. It is shown that smoothing of the down current surface waves is accompanied by a relatively high-frequency modulation while the profile of the opposing current is reproduced by the surface wave's envelope. The possibility of generation of an internal wave forerunner, that is a modulated surface wave packet, is established. Long surface waves can form the wave modulation forerunner ahead of the internal wave, while the relatively short surface waves create the trace of the internal wave. Modulation of surface waves by the periodic internal wave train may have the characteristic period less than the internal wave period and be no uniform while crossing the current zone. Surface wave excitation by internal waves, observable at their group resonance is efficient only on the opposing current.

並列關鍵字

stokes surface wave ； internal wave ； subsurface current ； Modulation equation