On Dynamical Decomposition of Multiscale Oceanic Motions

The ocean hosts a variety of fluid motions characterized by contrasting dynamical regimes and spatiotemporal scales. A practical decomposition of multiscale motions in realistic oceanic settings is crucial to advancing dynamical interpretation and prediction of oceanic processes, but remains a major challenge. To this end, methodology is developed in this study for decomposing multiscale oceanic motions based on their respective dynamical characteristics. Specifically, large‐scale currents and barotropic tides have the largest horizontal scales but contrasting frequencies; low‐mode internal gravity waves (IGWs) are well constrained by linear dispersion relations, whereas mesoscale flows are of relatively low frequency and with horizontal scales above the first baroclinic deformation radius; the intrinsic frequency of high‐mode IGWs (submesoscale flows) is above (well below) the inertial frequency. The validity and usefulness of the proposed methodology are demonstrated with a proof‐of‐concept application to simulated flows in the central basin of the South China Sea.