Mooring observed mode-2 internal solitary waves in the northern South China Sea

• Published in: Acta oceanologica Sinica Vol. 39; no. 11; pp. 44 - 51
• Main Authors: Chen, Liang, Xiong, Xuejun, Zheng, Quanan, Yuan, Yeli, Yu, Long, Guo, Yanliang, Yang, Guangbing, Ju, Xia, Sun, Jia, Hui, Zhenli
• Format: Journal Article
• Language: English
• Published: Beijing The Chinese Society of Oceanography 01-11-2020; Springer Nature B.V; Founctional Laboratory for Regional Oceanography and Numerical Modeling, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266237, China; First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China; Laboratory for Regional Oceanography and Numerical Modeling, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266237, China%Department of Atmospheric and Oceanic Science, University of Maryland, College Park, Maryland 20742, USA
• Subjects: Acoustics; Climatology; Coefficients; Compression; Density stratification; Diurnal; Diurnal variations; Earth and Environmental Science; Earth Sciences; Ecology; Engineering Fluid Dynamics; Environmental Chemistry; Internal tides; Internal waves; Isotherms; Laboratories; Marine & Freshwater Sciences; Mooring; Mooring systems; Oceanography; Pycnocline; Pycnoclines; Science; Solitary waves; South China Sea; internal tide; South China Sea; mooring observation; mode-2 internal solitary waves
• ISSN: 0253-505X; 1869-1099
• DOI: 10.1007/s13131-020-1667-0

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.