Energetics of Internal Tides and Lee Waves Under Different Background Flow Intensities

Abstract

Ocean mixing is a consequence of essential dynamic processes such as internal tides and lee waves that occur near the seafloor topography. Internal tides and lee waves are generated by barotropic tidal currents and geostrophic flows, respectively. Ocean current is composed of multiple flows; thus, internal tides and lee waves occur concurrently in the real ocean. In this paper, the Massachusetts Institute of Technology general circulation model (MITgcm) is used to conduct 2D numerical experiments. By varying background flow intensities, the energy and dissipation relationship between internal tides and lee waves are investigated. The results reveal that the internal tide beams become asymmetric due to the influence of Doppler shift. The lee wave structure gradually leads the wave field when the background flow velocity rises constantly. The presence of a background flow increases the energy portion of the high-mode wave by up to 15%–20%. Moreover, strong shear, owing to the background flow, considerably increases dissipation. When the background flow velocity is higher than the barotropic tidal current velocity, the isopycnal overturn triggered by the lee wave generates a dissipation of the same order of magnitude as the shear.