Experimental observations of internal wave turbulence transition in a stratified fluid

Recent developments of the weak turbulence theory applied to internal waves exhibit a power-law solution of the kinetic energy equation close to the oceanic Garrett-Munk spectrum, confirming weakly nonlinear wave interactions as a likely explanation of the observed oceanic spectra. However, finite-size effects can hinder wave interactions in bounded domains, and observations often differ from theoretical predictions. This paper studies the dynamical regimes experimentally developing in a stratified fluid forced by internal gravity waves in a pentagonal domain. We find that by changing the shape and increasing the dimensions of the domain finite-size effects diminish and wave turbulence is observed. In this regime, the temporal spectra decay with a slope compatible with the Garrett-Munk spectra. Different regimes appear by changing the forcing conditions, namely, discrete wave turbulence, weak wave turbulence, and strongly stratified turbulence. The buoyancy Reynolds number Reb marks well the transitions between the regimes, with weak wave turbulence occurring for 1 <= Reb <= 3.5 and strongly nonlinear stratified turbulence for higher Reb.