Propagation characteristics of near-inertial waves along the continental shelf in the wake of the 2008 Typhoon Hagupit in the northern South China Sea

A mooring and a real-time buoy allowed observation of oceanic and atmospheric variation in the wake of the 2008 Typhoon Hagupit in the South China Sea (SCS). In the present study, a regional ocean modeling system (ROMS) was used to explore the propagation characteristics of near-inertial waves (NIWs) along the continental shelf. The simulated NIWs were similar to the observation results. There were strong NIWs after the passage of Typhoon Hagupit, and the NIWs presented dual peaks, with one located in the mixed layer and the other at the thermocline. In the upper layer, the near-inertial kinetic energy on the left of the typhoon track was slightly weaker than that on the right. The responses of the ocean to the typhoon in shallow (<100 m) vs deep (>200 m) areas were different. The thermocline was significantly enhanced and deepened in shallow areas. The near-inertial kinetic energy of the thermocline in shallow areas occurred earlier and more intensely than that in the deep areas. The shallower mixed layer and the stronger thermocline in shallow areas are the main reasons for the difference in response. When the typhoon arrived, the mixed layer in shallow areas sank rapidly, causing the thermocline to sink, and the thermocline strength to increase and the thickness to decrease. The thermocline triggered NIWs during its compression. High compression and a strong thermocline result in powerful NIWs.