[AOS24-02] Direct numerical simulation of stratified turbulence generated by local instability of internal gravity waves
Keywords:internal waves, turbulence, direct numerical simulation
This time, we demonstrate a particular case, turbulence generation in a small-amplitude internal wave. Even though this wave does not cause any overturn or shear instabilities, a striped pattern of disturbance is exponentially amplified due to parametric instability. When the amplitude of this disturbance reaches a threshold level, secondary instability arises to produce much smaller-scale random fluctuations. Passing through these two stages, wave energy is transferred into turbulence energy and will be eventually dissipated. Different from the classical Kelvin-Helmholtz instability, a large part of the turbulent potential energy is supplied from the outer wave component and is directly used for mixing to raise the background potential energy. The resulting mixing efficiency is higher than the typical value in the ocean by several factors, a finding to be explored further in future studies.