Energy Conversion of Ocean Currents to Lee Waves over Seamounts Globally

Abstract Generation of oceanic lee waves by quasi-steady flows impinging on rough topography is believed to be an important contributor to the oceanic energy cascade, which dissipates the kinetic energy of the large-scale circulations and potentially supports strong local mixing, thus playing an important role in global oceanic heat transport and the carbon cycle. Previous studies have focused on the energy conversion of lee waves and its parameterization over small-amplitude topography with the Froude number Fr ≫ 1. However, the magnitude of global energy conversion to lee waves over seamounts with Fr ≪ 1 remains unclear. In this work, the lee-wave energy conversion from ocean currents over seamounts is evaluated based on an extended lee-wave theory using a seamount census (24 643 seamounts) and climatological ocean data. Before the application of the extended lee-wave theory, realistic numerical simulations of some seamounts are conducted to demonstrate a good performance of the theory in reproducing the lee-wave energy conversion over seamounts. The results show that the global total lee-wave conversion over seamounts is 0.68 GW in winter (defined here as February in the Northern Hemisphere and August in the Southern Hemisphere) and is 0.42 GW in summer (August in the Northern Hemisphere and February in the Southern Hemisphere) with a strong seasonal variation, of which 94% and 92% are attributed to the Southern Ocean, respectively. The averaged energy flux over the global seamounts is 0.12 mW m −2 in winter and 0.09 mW m −2 in summer. The strong lee-wave energy flux makes seamounts the candidate regions for enhanced mixing, potentially exerting significant influence on local dynamics and ecological environments.