1120 / 2024-09-20 13:44:31

Internal Lee Wave Generation and Modulation by Tidal Flows

internal tides,lee wave,energy flux,global

Session 70 - Internal Waves and Ocean Mixing

Internal tides and internal lee waves are two kinds of internal waves in the deep ocean, which have a significant influence on ocean circulation and stratification. Previous works concentrated the generation of internal waves by either geostrophic flow or barotropic tide alone. In this study, the internal wave generation by joint effects of steady and tidal flows over a small symmetric ridge is investigated using a two-dimensional primitive equation model. The model is set up in a linearly stratified fluid, with a rigid-lid and no-rotational approximation. Here we considered several cases, from linear to nonlinear, to investigate the energetics of internal waves, e.g., energy flux, calculated by linear theory which was raised by Bell (1975) and revisited by Nikurashin(2014), Shakespeare (2020) and so on. The generation is strongly asymmetric because of the Doppler shift. When the lee wave Froude number and tidal excursion are approximately 1, the energy flux calculation from model result is greater than that based on linear theory, even exceeding 2~5 times. Furthermore, we recalculated the global energy flux generated by internal wave in deep sea, using a higher resolution of topographic data SYNBATH (SYNthetic BATHymetry (Sandwell,2022)) and CMEMS (Copernicus Marine Environment Monitoring Service) reanalysis dataset. The result shows that about 0.55TW was generated by the internal lee waves alone, and 0.44TW when considering joint effects of tidal and steady background currents, which is suppressed by 20%. In the global ocean, the total energy flux is 2.57TW from barotropic to baroclinic, including 0.44TW from internal lee waves and 0.99TW from the M₂ tide. We are making efforts to provide a more accurate diagnosis of the distribution of internal wave energy flux in the global oceans by jointly considering the effects of steady and tidal flows. Future parameterizations in model ought to include the coupling mechanism of internal waves.