The Evolution of Large-Amplitude Internal Gravity Wavepackets

Colloque avec actes et comité de lecture. Internationale.International audienceThe interaction between internal gravity wavepackets and their associated wave-induced mean flow is shown to dominate their weakly nonlinear evolution at early times. Sufficiently large amplitude waves either grow in amplitude as the wavepacket narrows or decrease in amplitude as the wavepacket broadens due to nonlinearly enhanced dispersion depending on whether the frequency is respectively greater or less than the frequency of internal waves having the fastest vertical group velocity. This is true whether the waves are horizontally periodic or horizontally compact. In non-uniformly stratified fluid, the weakly nonlinear effect acts to enhance or retard transmission of the waves across a localized evanescent region depending upon the wave amplitude and relative frequency