Geophysical turbulence dominated by inertia–gravity waves

Abstract

Recent evidence from both oceanic observations and global-scale ocean model simulations indicate the existence of regions where low-mode internal tidal energy dominates over that of the geostrophic balanced flow. Inspired by these findings, we examine the effect of the first vertical mode inertia–gravity waves on the dynamics of balanced flow using an idealized model obtained by truncating the hydrostatic Boussinesq equations on to the barotropic and the first baroclinic mode. On investigating the wave–balance turbulence phenomenology using freely evolving numerical simulations, we find that the waves continuously transfer energy to the balanced flow in regimes where the balanced-to-wave energy ratio is small, thereby generating small-scale features in the balanced fields. We examine the detailed energy transfer pathways in wave-dominated flows and thereby develop a generalized small Rossby number geophysical turbulence phenomenology, with the two-mode (barotropic and one baroclinic mode) quasi-geostrophic turbulence phenomenology being a subset of it. The present work therefore shows that inertia–gravity waves would form an integral part of the geophysical turbulence phenomenology in regions where balanced flow is weaker than gravity waves.

Turbulent exchanges between near-inertial waves and balanced flows

“…At early times we observed that the interaction with waves resulted in breaking up of vortices, generating a wide range of small-scale structures in the balanced flow. Qualitatively similar turbulence phenomenology characterized by waves breaking up vortices was seen in the two-dimensional experiments described in Thomas & Yamada (2019) and Thomas & Arun (2020). In our experiments in the SW regime, although waves facilitated the generation of small-scale features in the balanced flow, the small-scale vortices were seen to gradually merge.…”

Geoinspired soft mixers

“…This process is also found for internal waves in stratified flows (Staquet & Sommeria 2002; Dauxois et al. 2018; Thomas & Yamada 2019) and for inertial waves in rotating flows (Yarom & Sharon 2014), where it generates wave turbulence. For a precessing cylinder, Lagrange et al.…”

“…This mechanism, also called parametric instability, is classical for surface waves, where a harmonic wave can excite two sets of waves with different wavelengths (Craik & Leibovich 1976;Miles & Henderson 1990;Francois et al 2013). This process is also found for internal waves in stratified flows (Staquet & Sommeria 2002;Dauxois et al 2018;Thomas & Yamada 2019) and for inertial waves in rotating flows (Yarom & Sharon 2014), where it generates wave turbulence. For a precessing cylinder, Lagrange et al (2011) predicted theoretically that the most unstable free modes have azimuthal wavenumbers m = 5 and m = 6 for a large range of aspect ratios.…”

Relative Dispersion in the Antarctic Circumpolar Current

“…One cannot entirely discount the possibility that small scale features in the flow might be present that can lead to cumulative dispersion. Such flow dynamics in the deep ocean can potentially result from interaction between internal waves and balanced flows (Thomas and Yamada 2019), or more esoteric flow features referred to as vortical modes, which result due to breaking waves creating mixed patches that then coalesce due to an inverse cascade (Sundermeyer et al 2005;Polzin and Ferrari 2004). Thus, the case on the true nature of stirring in deep ocean is not closed, and more dedicated observational work needs to be done to untangle these interesting complexities.…”