Interfacial gravity currents. I. Mixing and entrainment

Experiments are performed to examine mixing and transport due to an intrusive gravity current in a two- and three-layer fluid. Successive passages of the intrusion act to increase the depth of the middle layer. The observed broadening rates and the deposition of potential energy are compared with theories that neglect mixing and entrainment processes. As the middle layer widens, a transition in the mass transport by the intrusion is observed: in a two-layer fluid the intrusion transports mass along the entire length of the interface; in a three-layer fluid with sufficiently deep middle layer the intrusion transports mass over a limited distance and simultaneously excites large-amplitude internal wave modes and solitary internal waves.