The effect of strong shear on internal solitary-like waves

Abstract

Large-amplitude internal waves in the ocean propagate in a dynamic, highly variable environment with changes in background current, local depth, and stratification. The Dubreil–Jacotin–Long, or DJL, theory of exact internal solitary waves can account for a background shear, doing so at the cost of algebraic complexity and a lack of a mathematical proof of algorithm convergence. Waves in the presence of shear that is strong enough to preclude theoretical calculations have been reported in observations. We report on high-resolution simulations of stratified adjustment in the presence of strong shear currents. We find instances of large-amplitude solitary-like waves with recirculating cores in parameter regimes for which DJL theory fails and of wave types that are completely different in shape from classical internal solitary waves. Both are spontaneously generated from general initial conditions. Some of the waves observed are associated with critical layers, but others exhibit a propagation speed that is very near the background current maximum. As such they are not freely propagating solitary waves, and a DJL theory would not apply. We thus provide a partial reconciliation between observations and theory.