Presenter: Youran Li (UCSD)

Description:
Turbulence drives vertical transport of water, heat, carbon, and other important tracers, influencing the ocean general circulation and climate. In the Southern Ocean, turbulent kinetic energy (TKE) dissipation is thought to be the ultimate sink for the wind energy input. The generation, propagation, and breaking of internal waves (IWs) are important as IW interactions can lead to this TKE dissipation. A central aim of this study is to characterize the intensity and spatio-temporal distribution of the meridional IW energy flux diagnosed from MITgcm llc4320, a global ocean simulation with a horizontal resolution of 1/48^o, 90 vertical levels, and internal tides.  A decomposition into time scales shorter than 2 days is used to extract high-frequency variability associated with IWs. Our analysis covers Southern Hemisphere winter (May 29-Nov 15, 2012). The meridional IW energy flux is quantified across four latitudes (35S, 45S, 55S, and 65S) by computing the velocity-pressure correlations, <v’p’>. In the 55-65S band, we find a convergence of IW energy (1.3x10⁴MW), while in the 45-55S band, we find a divergence of IW energy (7.4x10³MW). Poleward of 65S, a convergence of 2.5x10²MW of IW energy is found. With bandpass filtering, the computation is performed for the diurnal, semidiurnal, and near-inertial band. Special attention is paid to the regions with rough topography and bottom flows associated with strong ACC jets, and to the periods when storms pass. To better characterize the propagation of IW energy flux, we decompose v’ and p’ into vertical normal modes and compute the IW energy flux of each mode. The maps of IW energy fluxes suggest where TKE dissipation from non-local energy inputs are significant.