Non-linear fate of internal wave attractors

TL;DR

This study investigates how internal wave attractors in stratified fluids become unstable and break down due to parametric subharmonic instability, explaining their elusive nature in natural environments with large amplitude forcing.

Contribution

It demonstrates the nonlinear instability mechanism of internal wave attractors through laboratory experiments, revealing the energy transfer pathways involved.

Findings

Attractors are destroyed by parametric subharmonic instability.

Triadic resonance facilitates energy transfer from large to small scales.

Large amplitude forcing can prevent the observation of attractors in nature.

Abstract

We present a laboratory study on the instability of internal wave attractors in a trapezoidal fluid domain filled with uniformly stratified fluid. Energy is injected into the system via standing-wave-type motion of a vertical wall. Attractors are found to be destroyed by parametric subharmonic instability (PSI) via a triadic resonance which is shown to provide a very efficient energy pathway from long to short length scales. This study provides an explanation why attractors may be difficult or impossible to observe in natural systems subject to large amplitude forcing.