ON THE BREAKDOWN INTO TURBULENCE OF PROPAGATING INTERNAL WAVES

The breakdown of propagating internal waves is studied using linear st ability analysis and direct numerical simulations. Sinusoidal wave tra ins in a uniformly stratified, non-rotating environment are considered . Cases are addressed with differing wave amplitudes and directions of propagation. For large-amplitude waves it is found that the primary i nstabilities are both two- and three-dimensional. It is also found tha t there is no qualitative difference in the breakdown process for wave s with amplitude slightly below or slightly above the amplitude of inc ipient overturning. For the parameter regimes considered, the breakdow n process could not be attributed to convective or shear instability a lone, but a combination of the two. Owing to the growth of instabiliti es, local patches of statically unstable fluid and also of intense she ar form, leading ultimately to local patches of turbulence.