Intrusions and solitons: Propagation and collision dynamics

Triggering and evolution of internal solitary waves (ISWs) generated by intrusive gravity currents (IGCs) propagating into a stratified ambient fluid is analyzed by laboratory experiments. After the release of a fluid of uniform density, intermediate with respect to the upper (lower-density) and lower (higher-density) layers in the channel, the IGC develops and flows downstream, intruding into the pycnocline. Near the IGC leading front, the compression of the upper layer generates ISWs: they gradually separate from the current that propagates slower. Shoaling downstream over a uniform sloping boundary, solitons break and partially reflect. We investigate the dynamics of the interaction between the reflected ISWs and the incoming IGC. During the engage, an increase in the ISW celerity occurs, leading the celerity of the reflected waves to be even larger than the incident wave. Our analysis shows how both ISWs and IGCs can significantly change their features as they experience a change of the density structure in the water column. This is expected to occur, for example, in stratified small-scale basins, where river plumes intrude the seasonal thermocline. The radial ISWs, originated by IGCs, can then be reflected by the adjacent bottom bathymetry, spreading against the intrusive current from which they are generated.