Latitudinal dependence of wind-induced near-inertial energy

Mid-latitude storms, accounting for the majority of wind energy input to near-inertial motions in the ocean, are known to shift their track significantly from one year to another. The consequence of such storm track shifts on wind-induced near-inertial energy (NIE) is yet unknown. Here, the latitudinal dependence of wind-induced NIE is first analysed in the framework of the slab model and then tested using two numerical ocean models. It is found that the NIE input by pure inertial wind stress forcing, which dominates the wind energy input to near-inertial motions, is independent of latitude. As a consequence, the NIE generated by white-noise wind stress forcing is also latitudinally independent. In contrast, the NIE generated by red-noise wind stress forcing shows strong dependence on latitude owing to longer inertial periods at lower latitudes capable of sampling greater inertial wind stress forcing. Given that the observed surface wind stress spectra are red, results from this study suggest that an equatorward shift of the storm track is likely to result in an increase in wind-induced NIE in the ocean, while the opposite is true for a poleward shift.