南海西北部半日内潮参量次谐频不稳定生成的近惯性波研究

SEMIDIURAL TIDE PARAMETETRIC SUBHARMONIC INSTABILITY INDUCED NEAR-INERTIAL WAVES IN NORTHWESTERN SOUTH CHINA SEA

为了研究非临界纬度上参量次谐频不稳定(parametric subharmonic instability, PSI)过程生成的近惯性波(near-inertial wave, NIW),本文基于国家重点研发项目的准实时传输深海潜标资料,对内波速度谱、近惯性流速和动能、D_(2)-f(半日频减惯性频)流速和动能、半日内潮流速和动能以及混合的时间分布特征进行了研究分析。平板模型与双相干谱分析表明,南海西北部陆坡区上层海洋出现的非风生近惯性波是由半日内潮PSI过程生成的,同时也会生成D_(2)-f内波。在发生显著PSI过程的深度上,生成的近惯性能量与全日内潮能量相当,生成的D_(2)-f能量与半日内潮能量相当,表明PSI过程生成的近惯性波和D_(2)-f内波是相当重要的。细尺度参数化方法结果显示PSI过程期间混合出现明显增强,但其增加的大小是中度的。

In order to study the near-inertial wave(NIW) generated by the parametric subharmonic instability(PSI)process at non-critical latitudes, this paper examines the internal wave velocity spectrum, near inertial velocity and kinetic energy, D_(2)-f(semidiurnal frequency minus inertial frequency) velocity and kinetic energy, semidiurnal tidal velocity and kinetic energy, and the time variation of turbulent mixing based on the data of quasi-real-time transmission subsurface mooring system. The slab model and bicoherence spectrum analysis show that the non-wind-generated near inertial waves appearing in the upper ocean are generated by the PSI of semidiurnal internal tides. The PSI not only generates diurnal internal waves, but also produces inertial frequency and D_(2)-f motions in the non-critical latitudes of the Northwestern Slope of the South China Sea. At some depth where the PSI process is discernible, the near-inertial energy generated by the PSI is equivalent to the diurnal tidal energy, and the D_(2)-f energy is equivalent to the semidiurnal tidal energy. In addition,significant PSI processes usually occur during strong semidiurnal movements. The results of the fine-scale parameterization method shows that the mixing is obviously enhanced during the PSI process, but the increase is moderate.