Estimating the Geostrophic–Ageostrophic Transition Scale in Ocean Currents From Wind Generated Waves

Abstract SWOT resolves sea surface height at spatial scales where geostrophic balance may break down and ageostrophic motions become significant, making identification of the transition scale essential. We test whether wind generated waves provide an independent diagnostic of this transition. WAVEWATCH III was forced with high resolution surface currents decomposed into geostrophic and ageostrophic components for two contrasting regimes: an energetic Brazil Current region and a calmer South Atlantic interior. Wavenumber spectra of significant wave height yield crossover scales consistent with those inferred from current KE spectra. We also examine the wave action flux after decomposition into rotational and divergent transport components. In the Brazil Current, the flux crossover aligns with the KE transition scale, whereas coherent swell weakens the correspondence in the interior South Atlantic.