Jeudi 9 janvier à 14h00, salle des séminaires IRPHE
Abstract: Internal gravity waves propagate in the bulk of stratified flows like the ocean. Their study is necessary because they impact the dynamics at many spatial and temporal scales, shaping the large-scale flows and influencing the small-scale mixing.
When the interactions between waves are weakly nonlinear, the weak wave turbulence theory (WWT) gives a theoretical framework to study such waves. Namely, it allows us to derive a kinetic equation describing the evolution of the wave energy spetrum. This equation is interesting because it gives access to the wave dynamics on kinetic (long) time scales due to wave-wave interactions. The theory also predicts steady scale-invariant solution(s) to the kinetic equation for many systems and discusses finite-size effects.
In this talk, I present some recent results on stratified turbulence emphasizing the role of wave on large-scale flow formation: (i) We obtain predictions for the typical size and the typical velocity of the large-scale flow using WWT arguments on finite size effects, and validate the predictions using 2D direct numerical simulations; (ii) We perform forced dissipated simulations of the kinetic equation for 3D internal gravity waves. The simulations allow us to observe the development of the energy spectrum and reveal the importance of non-local interactions (with waves of very different wave vectors modulus and frequency) in forming the large-scale flow.