Vertical Structure of Barotropic-to-Baroclinic Tidal Energy Conversion on a Continental Slope

Horizontal distribution of the vertically integrated barotropic-to-baroclinic energy conversion has been widely studied to examine the generation of internal tides at steep topography. The vertical structure of the energy conversion that provides insights into the associated dynamics, however, is masked by the often used depth-integrated approach. Here, we reveal the vertical profile of barotropic-to-baroclinic energy conversion by employing an idealized ocean model in a slope-shelf context forced by M-2 barotropic tidal flow. The model shows two vertically separated hotspots of energy conversion, one near the sloping bottom and the other at the thermocline, resulting from the stronger vertical velocity and enhancement of the density perturbation, respectively. Isolation of the hotspots demonstrates that baroclinic energy generated in the bottom layer radiates toward onshore and offshore primarily in the form of internal wave beams, whereas that generated at the thermocline propagates away in the form of internal wave modes. Although energy converted at the thermocline contributes to only a small portion of the total energy conversion, it plays an important role in onshore baroclinic energy radiation and can be significantly affected by the internal wave activity at the bottom layer. With a fixed bottom topography, the percentage of baroclinic energy generated at the thermocline is linearly related to a body force exerted by the barotropic tidal flow over topography that can be estimated analytically. This provides a convenient way to estimate the overall barotropic-to-baroclinic energy conversion over a continental slope in the real ocean by measuring the energy conversion in the thermocline only.

Automated summary

This study reveals the vertical distribution of barotropic-to-baroclinic energy conversion in a slope-shelf setting, showing two hotspots of energy conversion at the bottom and thermocline, respectively. The study also indicates the significance of baroclinic energy generated at the thermocline for onshore energy radiation.