What is the “Near-Inertial” Band and Why Is It Different from the Rest of the Internal Wave Spectrum?

TLDR

The near‑inertial portion of the internal wave spectrum dominates and differs from other frequency bands. Surface‑generated waves propagate equatorward until their frequency exceeds the local inertial frequency, preventing reflection or scattering from the seafloor. The resulting excess frequency is about 10 % of the inertial frequency at midlatitudes, matching observations of depth‑dependent peak frequency over smooth topography and the narrow band with little upward energy, indicating that bottom‑topography interactions are as important as wave‑wave interactions for controlling energetic internal waves and ocean mixing.

Abstract

The "near-inertial" part of the internal wave continuum is dominant and also different from the rest of the spectrum. A simple possible reason for the difference is that waves generated at the surface are not reflected or scattered from the seafloor until they have propagated equatorward to a latitude where their frequency exceeds the local inertial frequency. This excess is easily estimated and is of the order of 10% of f at midlatitudes. The estimate is in reasonable agreement with data on the depth dependence of the peak frequency over smooth topography and on the frequency band within which there is little upward propagating energy. Internal wave propagation and interactions with bottom topography may thus be just as important as wave–wave interactions in controlling the energetic parts of the internal wave spectrum and, hence, in determining mixing rates in the ocean.