Intermittent Generation of Nonlinear Internal Waves on Continental Shelf

Internal waves have a wide range of scales but are typically unresolved in climate or global models. With an unprecedented capability of observing and simulating these processes, they are becoming increasingly important to quantify the upscale effect of these processes. As the largest marginal sea in the western Pacific, the South China Sea has the most energetic and frequent internal waves around the world. These waves are also affected by multiscale processes, climate changes, and anthropogenic impacts. There have been considerable advances in exploring the generation and propagation of internal waves in recent years. However, the understanding of the formation and fate of internal solitary-like waves on the continental shelf is still very limited. It is widely accepted that these internal waves generally originate from the Luzon Strait. They usually have regular occurrence and are phase-locked to tidal forcing in the Luzon Strait. However, we present field measurements showing an irregular occurrence of nonlinear internal waves on the northern shelf of the South China Sea. This irregular occurrence is in striking contrast to the prominent predictability of internal waves originating from the Luzon Strait. We reveal that the intermittent nature of the occurrence is due to the local generation of nonlinear internal waves on the continental shelf, in addition to the fission of shoaling internal waves. The results reported here are expected to apply to other shelf regions of the world's oceans.