Breaking of unsteady lee waves generated by diurnal tides

Abstract

Diapycnal mixing caused through breaking of large‐amplitude internal lee waves generated by sub‐inertial diurnal tides, which are modulated with a 18.6‐year period, is hypothesized to be fundamental to both the intermediate‐layer ventilation and the bi‐decadal oscillation around the North Pacific Ocean. The first observational evidence of such wave breaking is presented here. The breaking wave observed had ∼200 m height and ∼1 km width, and its associated diapycnal mixing was estimated to be ∼1.5 m2 s−1, with a temporal average ∼104 times larger than typical values in the open oceans. Our estimate suggests that a similar mixing process occurs globally, particularly around the Pacific and Antarctic Oceans.