Presenter: Miguel Solano (The University of Southern Mississippi)

Description:
Although internal tides are recognized as an important pathway between the barotropic tide and turbulent dissipation, most studies have focused on the (semi-)diurnal frequency band and the linear terms in the energy balance. However, in regions with strong nonlinear internal wave (NLIW) activity, a significant portion of the wave energy is contained in the higher harmonics and the nonlinear advective fluxes, which arise from wave-wave and wave-mean flow interactions. In this study, we diagnose the nonlinear internal tide energy balance in a realistically forced global Hybrid Coordinate Model (HYCOM) simulation at 1/25° (4 km) horizontal resolution. The velocity and density fields are band-passed at semi-diurnal and supertidal frequencies and the time-mean and depth-integrated energy terms are computed. While the semi-diurnal pressure flux dominates over the advective and supertidal pressure fluxes in most of the ocean, the advective and supertidal pressure fluxes make up to 50% of the total flux in areas where solitary waves have been detected in Synthetic Aperture Radar (SAR) images (Jackson et al., 2012). Zonal averages show that around the equator approximately 15% of the pressure flux is in the supertidal band, decreasing sharply outside the tropics. To better understand the evolution of internal tides in HYCOM we analyze the energetics along the internal wave beams radiating from the Amazon shelf, the Bay of Bengal, and the Mascarene ridge. We compare the HYCOM simulation with a published 100-m nonhydrostatic Massachusetts Institute of Technology general circulation model (MITgcm) simulation at the Mascarene ridge. The solitons in the nonhydrostatic simulation have wave lengths of ~1 km and frequencies of 48 cpd and are clearly not resolved by HYCOM’s 4 km grid. The relatively coarse resolution prevents a proper energy cascade, trapping the nonlinear energy at the supertidal frequencies of 4-6 cpd.