Interaction Between Internal Solitary Waves and an Isolated Atoll in the Northern South

Interaction between Internal Solitary Waves and an Isolated Atoll in the Northern South China Sea

Guan-Yu Chen

Institute of Applied Marine Physics and Undersea Technology,
NationalSunYat-SenUniversity

Co-author: Rei-Jon Wu, Yu-Hwui Wang

In the last few years, there have been numerous numerical and field studies focused on the internal solitary wave (ISW) in the South China Sea. These studies conclude that the wave is phase-locked with the astronautic tide. The satellite image also shows that the wave is generated in the LuzonStrait and propagates westward toward Dongsha Atoll (Liu and Hsu, 2004).

Periodic temperature drops up to eight degrees Centigrade in the Dongsha Atoll has been reported and considered as the result of ISW (Wang et al. 2007). The cold water event occurs daily and lasts for a few hours. The time scale is much longer than that of the ISW. To further understand the physical process, detailed numerical simulation on the interaction of the Dongsha Atoll and the ISW is carried out by the Princeton Ocean Model (POM). An internal solitary wave is found to become asymmetric and then break in the shoaling process. Then, a violent tidal bore forms and runs up the slope, bringing up the cold deep water to the shallow waters. The simulated temperature variation and the flow field are very similar to the event of largest temperature drop in the field measure where the flow field is dominated by the ISW.

It is found that this internal surge cannot be generated by an internal tide which is too mild to break in the short shoaling process. The narrow step around the atoll also plays a very important role in the sense that the cold deep water is detained on the step and hence can affect the local ecosystem for a long time. On the contrary, the numerical simulation shows that in the absence of the step, the cold water will runs up and down in a much shorter time.

References:

Liu, A. K., and M. K. Hsu (2004): Internal wave study in the South China Sea using Synthetic Aperture Radar (SAR), INT. J. REMOTE SENSING, 10-20, vol. 25, No. 7-8, 1261-1264.

Wang, Y.-H., C.-F. Dai and Y.-Y. Chen, 2007, Physical and ecological processes of internal waves on an isolated reef ecosystem in the South China Sea, Geophysical Research Letter, 34, L18609, doi:10.1029/ 2007GL030658.