Characteristics, Generation, and Propagation of Nonlinear Internal Waves Observed in the Northern East China Sea

Oceanic nonlinear internal waves (NLIWs) play an important role in regional circulation, marine biogeochemistry, energetics, vertical mixing, underwater acoustics, marine engineering, and submarine navigation, most commonly generated by the interaction between barotropic tides and bathymetry. However, our understanding of their characteristics, generation, and propagation is still far from complete in many water bodies. Here, we present the characteristics of NLIWs observed from moored and underway observation in the northern East China Sea during May 15-28, 2015 and discuss their generation and propagation. The NLIWs observed during the experiment were characterized by an amplitude ranging from 4 to 16 m, width ranging from 380 to 600 m, and propagated southwestward at a speed of 0.64–0.72 m s⁻¹. Groups of NLIWs were predominantly observed during, or a couple of days after, the period of spring tides, with a time interval 24–96 min shorter than the canonical semidiurnal period (12.42 h; M₂); this is in contrast to those found in many other regions that have a phase-locking to the barotropic semidiurnal tides. The remote generation and propagation of the NLIWs from potential generation sites into the study area under time-varying stratification support the fact that the time interval departed from the semidiurnal period. Our results have substantial implications for turbulent mixing and ocean circulation in regions where the shelf is broad and shallow. The NLIWs generated from multiple sources propagate in multiple directions with propagating speeds varying over days depending on stratification.