Latitude dependence of the fate of internal tide beams
We find that solitary waves, indicated by the propagation of interfacial waves, can be generated where the internal tidal beam intersects the pycnocline with the Bay of Biscay stratification, but not with the Hawaii stratification profile. The Bay of Biscay experiments also show more horizontal ”ducting” of energy in the pycnocline, at both superharmonic as well as subharmonic frequencies.
Both sets of experiments show transfers of energy to subharmonic frequencies, accompanied by the appearance of energy at small vertical scales, suggesting the presence of triadic resonant interactions. Sub-M2 secondary waves are observed both equatorward and poleward of the critical latitude (29o). Triadic resonant interaction energy transfers are largest near the critical latitude, where, away from the boundary forcing, the energy in the secondary waves can become more than three times the energy remaining at M2. At 35o the energy in the sub-M2 secondary waves can be up to 60% of the remaining M2 energy. Energetic triadic resonant interactions can result in degradation of the incident tidal beam which interferes with the generation of the interfacial waves in the pycnocline.