Nonlinear wave-wave interactions in stratified flows: Direct numerical simulations

TL;DR

This paper uses direct numerical simulations of simplified rotating stratified turbulence equations to explore how wave-wave interactions shape the energy spectra of internal waves in oceans, highlighting the dominance of near-inertial wave interactions.

Contribution

It demonstrates that simplified wave-only models can reproduce key features of oceanic internal-wave spectra and identifies the dominant role of near-inertial wave interactions in spectral formation.

Findings

Reproduces key features of oceanic internal-wave spectra

Shows energy accumulation at near-inertial waves

Identifies wave-wave interactions as primary spectral formation mechanism

Abstract

To investigate the formation mechanism of energy spectra of internal waves in the oceans, direct numerical simulations are performed. The simulations are based on the reduced dynamical equations of rotating stratified turbulence. In the reduced dynamical equations only wave modes are retained, and vortices and horizontally uniform vertical shears are excluded. Despite the simplifications, our simulations reproduce some key features of oceanic internal-wave spectra: accumulation of energy at near-inertial waves and realistic frequency and horizontal wavenumber dependencies. Furthermore, we provide evidence that formation of the energy spectra in the inertial subrange is dominated by scale-separated interactions with the near-inertial waves. These findings support oceanographers' intuition that spectral energy density of internal waves is the result of predominantly wave-wave interactions.