Prototypical Solitons in the South China Sea

When observed, so-called solitary waves are often found to evolve so rapidly that they cannot really be called solitary. Here we present detailed observations of waves in the deep South China Sea that we track for over 90 km, from ship and a satellite photo. The waves are mode-1, have amplitudes of 170 m, and move at 2.95 m/s. They have weak intrinsic shear, but are found to interact with pre-existing shear, perhaps triggering instabilities. However, on the whole, these waves appear to be non-dissipative and do not appreciably change amplitude, shape, or phase speed over 70 km. The shape and phase speed are well-fit by the Korteig-deVries equation, which allows us to estimate the kinetic energy (KE=1.1 GJ m-1) and available potential energy (APE=0.75 GJ m-1). Released over a tidal cycle, the lead two waves of this packet constitute 9 GW of energy heading towards Dongsha Island. Observations of other packets indicate that this was the peak in internal wave energy, with a spring-neap average closer to 2.5 GW.