Reabsorption of Lee-Wave Energy in Bottom-Intensified Currents

While lee-wave generation has been argued to be a major sink for the 1-TW wind work on the ocean's circulation, microstructure measurements in the Antarctic Circumpolar Currents find dissipation rates as much as an order of magnitude weaker than linear lee-wave generation predictions in bottom-intensified currents. Wave action conservation suggests that a substantial fraction of lee-wave radiation can be reabsorbed into bottom-intensified flows. Numerical simulations are conducted here to investigate generation, reabsorption, and dissipation of internal lee waves in a bottom-intensified, laterally confined jet that resembles a localized abyssal current over bottom topography. For the case of monochromatic topography with |kU(0)| approximate to 0.9N, where k is the along-stream topographic wavenumber, |U-0| is the near-bottom flow speed, and N is the buoyancy frequency; Reynolds-decomposed energy conservation is consistent with linear wave action conservation predictions that only 14% of lee-wave generation is dissipated, with the bulk of lee-wave energy flux reabsorbed by the bottom-intensified flow. Thus, water column reabsorption needs to be taken into account as a possible mechanism for reducing the lee-wave dissipative sink for balanced circulation.

Automated summary

Microstructure measurements in the Antarctic Circumpolar Currents find weaker dissipation rates of lee waves than predicted, suggesting reabsorption of wave radiation into bottom-intensified flows. Numerical simulations of a bottom-intensified, laterally confined jet show that only 14% of lee wave generation is dissipated, with the majority reabsorbed by the flow. Water column reabsorption needs to be considered as a possible mechanism for reducing the dissipative sink of lee waves in balanced circulation.