Internal solitary waves influence mixing, acoustic propagation, radar observations and offshore engineering design. Here, we report observations illustrating further mechanisms that may be responsible for their generation. Typically the waves form almost straight lines, consistent with the 2-dimensional behaviour of the flow near the channel center. The bifurcation normally occurs well upstream of the crest, but in strong tidal currents can be pushed downstream. Corresponding echo-sounding image of solitary waves.
Arrows indicate current vectors shown at same aspect ratio as figure and coded as to magnitude.
Upstream density profile in s t . Although we could not detect the moment of wave generation, the mechanism appears linked to the temporal evolution of the bifurcation, in which the waves radiate upstream as the bifurcation is forced downstream by the tidal current. In this and other similar examples, the waves were formed as the bifurcation moved downstream over the sill crest. Subsequent traverses showed that the bifurcation was pushed downstream by the increasing tidal current until it approached, but did not quite reach, the shape shown in Fig. Thus the waves in Fig.