Double ridge internal tide interference and its effect on dissipation in Luzon Strait

Abstract

Luzon Strait between Taiwan and the Phillipines features two parallel north-south oriented ridges. The barotropic tides that propagate over these ridges cause strong internal waves and dissipation. The energy dissipation mechanisms and the role of the baroclinic wave fields in this dissipation are investigated using numerical simulations with the MITgcm. The model is integrated over two-dimensional configurations along a zonal transect at 20.6±N for a maximum duration of a spring-neap cycle. Nearly all dissipation occurs at the steep ridge crests due to high-mode turbulent lee waves with horizontal scales of several kilometers and vertical scales of hundreds of meters. The spatial structure and timing of the predicted
velocities and dissipation agree with observations, and confirm the existence of these lee waves. The lee wave strength is greatly affected by the internal waves generated at the other ridge. When semidiurnal barotropic tides are dominant, the internal wave beams from both ridges nearly superpose after one surface reflection. The remotely generated internal waves from both ridges are therefore in phase with each other and the barotropic tides at the ridges. The barotropic to baroclinic energy conversion, energy flux divergence, ridge top velocities,
and dissipation are stronger compared to the sum of the single east and west ridge cases. When diurnal tides are dominant, the wave fields are more out of phase, and the conversion, divergence, and the dissipation are less than or equal to the single ridge cases combined.

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