Abstract
The mode-2 internal solitary waves (ISWs) generated by mode-2 internal tide (IT) are identified by mooring observations in the northern South China Sea (SCS) from 2016 to 2017. Two mode-2 ISWs with a re-appearance period of 24.9 h observed on 29 and 30 July 2016 are characterized by type-b ISWs. They occurred when the isotherms compressed obviously in the vertical direction. Modal decomposition of IT horizontal currents shows that the vertical compression of the isotherms is mainly caused by diurnal mode-2 IT. The analysis of the role of the density stratification reveals that a deeper and thinner pycnocline is favorable for generation of mode-2 ISWs rather than pycnocline intensity. By comparing the mode-2 nonlinear, dispersion coefficients and the Ursell numbers calculated based on the stratification associated with different kinds of ITs with the observation results, it is shown that the diurnal mode-2 IT plays a crucial role in the generation of the mode-2 ISWs. When the diurnal mode-2 IT interacts with the semidiurnal IT and causes a deeper and thinner pycnocline, the mode-2 ISWs are easily excited.
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The National Science and Technology Major Project under contract No. 2016ZX05057015; the National Natural Science Foundation of China (NSFC) under contract Nos 41376038, 40406009, 41806123 and 41506038; the NSFC-Shandong Joint Fund for Marine Science Research Centers under contract No. U1606405; the National Program on Global Change and Air-Sea Interaction under contract Nos GASI-03-01-01-02, GASI-02-IND-STSsum and GASI-IPOVAI-01-05; the Public Science and Technology Research Funds Projects of Ocean under contract No. 200905024; the National Key Scientific Instrument and Equipment Development Projects under contract No. 2012YQ12003908.
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Chen, L., Xiong, X., Zheng, Q. et al. Mooring observed mode-2 internal solitary waves in the northern South China Sea. Acta Oceanol. Sin. 39, 44–51 (2020). https://doi.org/10.1007/s13131-020-1667-0
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DOI: https://doi.org/10.1007/s13131-020-1667-0