Observations of shoaling internal wave transformation over a gentle slope in the South China Sea

[摘要] Four oceanographic moorings were deployed across the South China Seacontinental slope near 21.85 ∘  N, 117.71 ∘  E, from 30 Mayto 18 July 2014​​​​​​​ for the purpose of observing high-frequency nonlinearinternal waves (NLIWs) as they shoaled across a rough, gently slopingbottom. Individual waves required just 2 h to traverse the array andcould thus easily be tracked from mooring to mooring. In general, theamplitude of the incoming NLIWs tracked the fortnightly tidal envelope inthe Luzon Strait; they lagged by 48.5 h and were smaller than the wavespreviously observed to the southwest near the Dongsha Plateau. Two types of waves,a waves and b waves,​​​​​​​ were observed, with the b waves always leading thea waves by 6–8 h. Most of the NLIWs were remotely generated, but a fewof the b waves formed locally via convergence and breaking at the leadingedge of the upslope-propagating internal tide. Waves incident upon themoored array with amplitude less than 50 m and energy less than 100 MJ m −1 propagated adiabatically upslope with little change of form. Largerwaves formed packets via wave dispersion. For the larger waves, the kineticenergy flux decreased sharply upslope between 342 and 266 m, while thepotential energy flux increased slightly, causing an increasing ratio ofpotential-to-kinetic energy as the waves shoaled. None of the waves met thecriteria for convective breaking. The results are in rough agreement withrecent theory and numerical simulations of shoaling waves.

[学科分类] 自动化工程