Modal structure and propagation of internal tides in the northeastern South China Sea

• Published in: Acta oceanologica Sinica Vol. 38; no. 9; pp. 12 - 23
• Main Authors: Liu, Qian, Xie, Xiaohui, Shang, Xiaodong, Chen, Guiying, Wang, Hong
• Format: Journal Article
• Language: English
• Published: Beijing The Chinese Society of Oceanography 01.09.2019; Springer Nature B.V; School of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China; State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China%State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China%State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China%School of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China
• Subjects: Barotropic mode; Barotropic tides; Climatology; Continental shelves; Continental slope; Diurnal; Diurnal variations; Earth and Environmental Science; Earth Sciences; Ecology; Energy; Energy flux; Energy transfer; Engineering Fluid Dynamics; Environmental Chemistry; Fluctuations; Flux; Internal tides; Marine & Freshwater Sciences; Mooring; Ocean currents; Oceanography; Slopes; Tidal dynamics; Tidal energy; Tidal power; Tides; Topography (geology); Vertical profiles; South China Sea; South China Sea; internal tides; propagation; modal structure; scattering
• ISSN: 0253-505X; 1869-1099
• DOI: 10.1007/s13131-019-1473-1

The evolution of energy, energy flux and modal structure of the internal tides (ITs) in the northeastern South China Sea is examined using the measurements at two moorings along a cross-slope section from the deep continental slope to the shallow continental shelf. The energy of both diurnal and semidiurnal ITs clearly shows a ~14-day spring-neap cycle, but their phases lag that of barotropic tides, indicating that ITs are not generated on the continental slope. Observations of internal tidal energy flux suggest that they may be generated at the Luzon Strait and propagate west-northwest to the continental slope in the northwestern SCS. Because the continental slope is critical-supercritical with respect to diurnal ITs, about 4.6 kJ/m 2 of the incident energy and 8.7 kW/m of energy flux of diurnal ITs are reduced from the continental slope to the continental shelf. In contrast, the semidiurnal internal tides enter the shelf because of the sub-critical topography with respect to semidiurnal ITs. From the continental slope to the shelf, the vertical structure of diurnal ITs shows significant variation, with dominant Mode 1 on the deep slope and dominant higher modes on the shelf. On the contrary, the vertical structure of the semidiurnal ITs is stable, with dominant Mode 1.