Mesoscale to Submesoscale Wavenumber Spectra in Drake Passage

TLDR

The observed wavenumber spectra resemble predictions of isotropic interior quasigeostrophic turbulence. The study examines upper‑ocean horizontal wavenumber spectra in the Drake Passage using 13 years of shipboard ADCP measurements, satellite altimetry, and a high‑resolution numerical simulation. It employs 13 years of ADCP data, satellite altimetry, and a high‑resolution numerical simulation to analyze the spectra. The spectra follow a k⁻³ law between 10–200 km, are surface‑enhanced but depth‑independent, and deviate from isotropic QG turbulence below 40 km; ageostrophic inertia–gravity waves explain the discrepancy, contributing roughly half of near‑surface kinetic energy and sea‑surface height variance at 10–40 km.

Abstract

Abstract This study discusses the upper-ocean (0–200 m) horizontal wavenumber spectra in the Drake Passage from 13 yr of shipboard ADCP measurements, altimeter data, and a high-resolution numerical simulation. At scales between 10 and 200 km, the ADCP kinetic energy spectra approximately follow a k −3 power law. The observed flows are more energetic at the surface, but the shape of the kinetic energy spectra is independent of depth. These characteristics resemble predictions of isotropic interior quasigeostrophic turbulence. The ratio of across-track to along-track kinetic energy spectra, however, significantly departs from the expectation of isotropic interior quasigeostrophic turbulence. The inconsistency is dramatic at scales smaller than 40 km. A Helmholtz decomposition of the ADCP spectra and analyses of synthetic and numerical model data show that horizontally divergent, ageostrophic flows account for the discrepancy between the observed spectra and predictions of isotropic interior quasigeostrophic turbulence. In Drake Passage, ageostrophic motions appear to be dominated by inertia–gravity waves and account for about half of the near-surface kinetic energy at scales between 10 and 40 km. Model results indicate that ageostrophic flows imprint on the sea surface, accounting for about half of the sea surface height variance between 10 and 40 km.