Observations of semidiurnal M 2 internal tidal parametric subharmonic instability in the northeastern South China Sea

作者：Qian LIU,Xiaodong SHANG,Xiaohui XIE

摘要：Near-diurnal vertically-standing waves with high vertical wavenumbers k z were observed in the velocity and shear fi elds from a set of 75-d long ADCP moored in the northeastern South China Sea(SCS)away from the“critical”latitude of 28.8°.These enhanced near-diurnal internal waves followed a fortnightly spring-neap cycle.However,they always happened during semidiurnal spring tides rather than diurnal springs although strong diurnal internal tides with the fortnightly spring-neap cycle were prevailing,suggesting that they were generated via subharmonic instability(PSI)of dominant semidiurnal M 2 internal tides.When two semidiurnal internal tidal waves with opposite vertical propagation direction intersected,both semidiurnal subharmonic and super harmonic waves were largely intensifi ed.The observed maximum diurnal velocity amplitudes were up to 0.25 m/s.The kinetic energy and shear spectra further suggested that frequencies of daughter waves were not always perfectly equal to M 2/2.The superposition of two daughter waves with nearly equal frequencies and nearly opposite k z in a PSI-triad leaded to the vertically-standing waves.

发文机构：School of Naval Architecture and Ocean Engineering State Key Laboratory of Tropical Oceanography Southern Marine Science and Engineering Guangdong Laboratory State Key Laboratory of Satellite Ocean Environment Dynamics

关键词：internaltidesSouthChinaSea(SCS)resonantinteractionsrotaryspectraparametricsubharmonicinstability

分类号： P73[天文地球—海洋科学]