Geophysical Fluid Dynamics: Stratified Flows

Internal solitary waves (ISWs) are solitary waves that occur within stably stratified water columns where density changes are due to temperature, salinity, or both. The pycnocline, where density changes relatively quickly with depth, acts as a wave guide for such internal wave motion. ISWs are characterized by different modes. Mode-1 ISWs are the most frequently observed mode, and they displace isopycnals in one direction only (depression or elevation). Mode-2 ISWs displace isopycnals in two directions and are characterized by concurrent elevation and depression of isopycnals into the upper and bottom layers, respectively. Mode-2 ISWs are commonly observed as convex bulges propagating along the pycnocline, but recent studies

have suggested the presence of other types of profiles. Thus, experimental and numerical studies were performed to investigate the physical generation of such waves. Simulations were performed on an open-source Spectral Parallel Incompressible Navier-Stokes solver to observe the formation of multi-humped mode-2 waves. The numerical domain mimicked the laboratory wave flume with fluids of three different densities. The water column was stably stratified, and a lock release method was used to generate the ISWs due to buoyancy adjustment. Simulation results revealed that an intermediate layer offset is required to generate mode-2 waves with a multi-hump profile. It was also discerned that a leading mode-1 wave resulted in the humped morphology of the mode-2 waves.