A growth mechanism for topographic internal waves generated by an oscillatory flow

On the basis of ray tracing of individual waves generated at various phases of the tidal flow, an amplification mechanism is presented for a new class of topographically generated internal waves identified by Nakamura et al., which develop across a broad latitude range and can exist even above the c ritical latitude where the tidal frequency equals the inertial frequency. T he results show that unsteady lee waves are always amplified when the maxim um frequency is much smaller than the buoyancy frequency because their phas e speeds (amplitudes) are equal (proportional) to the tidal flow speed at t heir time of generation. Fast mixed tidal-lee waves are also effectively am plified, when the rotation effect is significant. Accordingly, amplificatio n of unsteady lee and fast mixed tidal-lee waves can occur even if the requ irements of previous theories (e.g., the critical slope and critical Froude number conditions) are not satisfied. Since the result here covers the gen eration and amplification processes of topographic internal waves across a broader parameter range than earlier theories, it should contribute to a be tter understanding of boundary mixing processes, especially in high-latitud e regions.