Scripps Institution of Oceanography, La Jolla, CA

(Manuscript received soon! , in final form soon!) Numerical process studies of an idealized upward propagating internal tide at 21◦S demonstrate a rapid transfer of energy (over only a few days) to waves of half the tidal frequency and smaller vertical scale. The energy transfer characteristics are consistent with Parametric Subharmonic Instability (PSI), a particular class of resonant wave-wave interactions previously thought too slow (timescales of weeks or months) to be an effective mechanism for extracting energy from the internal tide. Near sources, the internal tide is coherent, i.e. not well described by a random phase approximation. Consequently, the simulated transfer rates are much faster than theoretical predictions that rely on this approximation. The slow group velocities of recipient subharmonic waves constrain them to break near the generation site; overall 40 % of the tidal energy is dissipated locally. Further simulations indicate that the strength of this “tidal mixing hotspot ” is strongly latitude dependent. At the critical latitude of 28.9◦nearly 80 % of tidal energy is dissipated locally. Poleward of the critical latitude, M2/2 < f, PSI can not occur, and nearly all the generated tidal energy radiates away. 1