On the Origins of the Oceanic Ultraviolet Catastrophe

TL;DR

This paper derives a first-principles formula for oceanic internal wave energy fluxes, aligning with the Finescale Parameterization, and resolves paradoxes about energy cascades in ocean turbulence.

Contribution

It introduces a wave turbulence theory-based methodology to analytically compute energy fluxes, explaining the oceanic ultraviolet catastrophe.

Findings

Energy fluxes match the Finescale Parameterization in form and magnitude.

Predicts a direct energy cascade, contrary to previous inverse cascade assumptions.

Reinstates 'constant-downscale-flux' solutions as physically relevant.

Abstract

We provide a first-principles analysis of the energy fluxes in the oceanic internal wavefield. The resulting formula is remarkably similar to the renowned phenomenological formula for the turbulent dissipation rate in the ocean which is known as the Finescale Parameterization. The prediction is based on the wave turbulence theory of internal gravity waves and on a new methodology devised for the computation of the associated energy fluxes. In the standard spectral representation of the wave energy density, in the two-dimensional vertical wavenumber - frequency domain, the energy fluxes associated with the steady state are found to be directed downscale in both coordinates, closely matching the Finescale-Parameterization formula in functional form and in magnitude. These energy transfers are composed of a `local' and a `scale-separated' contributions; while the former is quantified numerically, the latter is dominated by the Induced Diffusion process and is amenable to analytical treatment. Contrary to previous results indicating an inverse energy cascade from high frequency to low, at odds with observations, our analysis of all non-zero coefficients of the diffusion tensor predicts a direct energy cascade. Moreover, by the same analysis fundamental spectra that had been deemed `no-flux' solutions are reinstated to the status of `constant-downscale-flux' solutions. This is consequential for an understanding of energy fluxes, sources and sinks that fits in the observational paradigm of the Finescale Parameterization, solving at once two long-standing paradoxes that had earned the name of `Oceanic Ultraviolet Catastrophe'.