Shoaling internal solitary waves

The evolution and breaking of internal solitary waves in a shallow upper layer as they approach a constant bottom slope is examined through laboratory experiments. The waves are launched in a two-layer fluid through the standard lock-release method. In most experiments, the wave amplitude is significantly larger than the depth of the shallow upper layer so that they are not well described by Korteweg-de Vries theory. The dynamics of the shoaling waves are characterized by the Iribarren number, Ir, which measures the ratio of the topographic slope to the square root of the characteristic wave slope. This is used to classify breaking regimes as collapsing, plunging, surging, and nonbreaking for increasing values of Ir. For breaking waves, the maximum interface descent, Hi, is predicted to depend upon the topographic slope, s, and the incident wave's amplitude and width, A(sw) and L-sw, respectively, as Hi similar or equal to 4sAswLsw. This prediction is corroborated by our experiments. Likewise, we apply simple heuristics to estimate the speed of interface descent, and we characterize the speed and range of the consequent upslope flow of the lower layer after breaking has occurred.