[1] The conversion of depression nonlinear internal solitons to elevation internal waves has been observed twice at the South China Sea continental shelf break. Shipboard X-band radar, tow-yo CTD, ADCP and high frequency acoustic flow visualization of the process are presented. The data focuses on up slope propagation of depression internal solitons from a water depth of $264 m to a water depth of $110 m. Dissipation by large amplitude shear instabilities was observed. The kinetic energy density was found to be a decreasing monotonic function of range with an energy dissipation rate coefficient of 0.063 km À1 . The rate of energy dissipation over the $16.5 km soliton propagation path was 0.17 W/m/m. Simple numerical models of the waveform evolution are qualitatively compared to the observations. The observations, extracted scale parameters and dissipation rates should be useful for testing a variety of evolution equation representations of internal soliton propagation.INDEX TERMS: 4544 Oceanography: Physical: Internal and inertial waves; 4568 Oceanography: Physical: Turbulence, diffusion, and mixing processes; KEYWORDS: Internal waves, solitons, fine structure mixing, dissipation Citation: Orr, M. H., and P. C. Mignerey, Nonlinear internal waves in the South China Sea: Observation of the conversion of depression internal waves to elevation internal waves,

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In order to understand the fluctuations imposed upon low frequency (50 to 500 Hz) acoustic signals due to coastal internal waves, a large multilaboratory, multidisciplinary experiment was performed in the Mid-Atlantic Bight in the summer of 1995. This experiment featured the most complete set of environmental measurements (especially physical oceanography and geology) made to date in support of a coastal acoustics study. This support enabled the correlation of acoustic fluctuations to clearly observed ocean processes, especially those associated with the internal wave field. More specifically, a 16 element WHOI vertical line array (WVLA) was moored in 70 m of water off the New Jersey coast. Tomography sources of 224 Hz and 400 Hz were moored 32 km directly shoreward of this array, such that an acoustic path was constructed that was anti-parallel to the primary, onshore propagation direction for shelf generated internal wave solitons. These nonlinear internal waves, produced in packets as the tide shifts from ebb to flood, produce strong semidiurnal effects on the acoustic signals at our measurement location. Specifically, the internal waves in the acoustic waveguide cause significant coupling of energy between the propagating acoustic modes, resulting in broadband fluctuations in modal intensity, travel-time, and temporal coherence. The strong correlations between the environmental parameters and the internal wave field include an interesting sensitivity of the spread of an acoustic pulse to solitons near the receiver.