SEMINAR: (What�s the Story) Internal Solitary Waves?

Internal solitary waves are large-amplitude internal waves usually characterized in a two-layer fluid as a hump-shaped disturbance whose structure does not change as it propagates at speeds faster than the long-wave speed. They are manifest at an atmospheric inversion as Australia’s Morning Glory and also result in the ocean from tidal forcing of the thermocline at the continental shelves. In laboratory experiments internal solitary waves are usually created by a lock-exchange mechanism similar to that used to create surface gravity currents. In the latter case, fresh water behind a gate is suddenly released into a uniformly saline ambient when the gate is vertically extracted. In the former case, the ambient is a two-layer fluid with fresh overlying salty water. If the depth of the fresh water layer in the ambient is relatively small, the resulting flow exhibits characteristics of both gravity currents and solitary waves. We examine this behaviour in both rectangular and cylindrical geometries for intrusions moving along at the interface of an approximately two-layer fluid. In both cases the intrusion is found to propagate at constant speed much further from the gate than predicted or observed for surface gravity currents because of interactions with solitary waves. Understanding these dynamics theoretically is particularly challenging in an axisymmetric geometry for which self-consistent evolution equations have yet to be developed. This talk will also present recent experiments examining sediment resuspension by internal solitary waves shoaling on a slope.