Refraction of near-inertial waves by submesoscale vorticity filaments

The interaction of near-inertial waves (NIWs) with submesoscale vorticity filaments is explored using theory and simulations. We study three idealised set-ups representative of submesoscale flows allowing for O (1) or greater Rossby numbers. First, we consider the radiation of NIWs away from a cyclonic filament and develop scalings for the decay of wave energy in the filament. Second, we introduce broad anticyclonic regions that separate the cyclonic filaments mimicking submesoscale eddy fields and analyse the normal modes of this system. Third, we extend this set-up to consider the vertical propagation and the radiation of NIW energy. We identify a key length scale Lₘ, dependent on the strength of the filament, stratification and vertical scale of the waves, that when compared with the horizontal scales of the background flow determines the NIW behaviour. A generic expression for the vertical group velocity is derived that highlights the importance of horizontal gradients for vertical wave propagation. An overarching theme of the results is that NIW radiation, both horizontally and vertically, is most efficient when Lₘ is comparable to the length scales of the background flow.