恒春海脊附近第二模态内孤立波的特征研究

以往通过地震海洋学方法发现的大多是第一模态内孤立波,本文在台湾岛以南恒春海脊处捕捉到了两个大振幅凸型第二模态内孤立波.利用叠前偏移剖面得到内孤立波的视相速度约为0.7 m·s^-1,其视传播方向沿地震测线从S到N,总体上满足较大最大振幅的波视相速度也较大的规律.地震海洋学剖面得到的振幅曲线观测值和理论方程计算出的第二模态内波振幅垂向变化理论值之间具有较好的一致性.通过叠前偏移剖面观察该内孤立波细结构的变化,发现在采集过程中,出现反射同相轴后翼变陡、分叉、合并的现象.由于密跃层中心偏离水层中心以及背景剪切流的影响,两个内孤立波尾部发育了高频内波,使得能量耗散增强.此外,第二模态内孤立波的生成和传播特征受到水体层结、黑潮、背景剪切流以及海底地形等多个因素的影响.

Study on the characteristics of mode-2 internal solitary waves near the Hengchun Ridge

Most of the internal solitary waves discovered by seismic oceanography method are first-mode internal solitary waves. In this paper, two convex mode-2 internal solitary waves with large amplitude were captured in the Hengchun Ridge south of Taiwan Island by seismic oceanography method. The apparent phase speeds of ISW1 and ISW2 are about 0.7 m·s-1 by using the pre-stack migration sections of the Common Offset Gathers. The apparent propagation direction is from S to N along the seismic survey line. The apparent phase speed of ISW1 with a larger maximum amplitude is larger. Results show that the observed amplitude values obtained from seismic oceanography section conforms to the theoretical amplitude values calculated by the theoretical equation. The variation of the fine structure of the mode-2 internal solitary wave group is observed by the prestack migration section. It is found that the back edge of the reflection event steepens, bifurcates and merges during the acquisition process. Because the center of the pycnocline deviates from half depth of water column, and the effect of background shear flow, the high frequency internal wave develops in the tail of the two second-mode ISWs, which enhances the energy dissipation. In addition, the formation and propagation characteristics of mode-2 internal solitary waves are affected by many factors, such as stratification, Kuroshio, background shear current and seabed topography.