Laboratory experiments on mass transport by large amplitude mode-2 internal solitary waves

The existence of internal solitary waves (ISWs) in the coastal ocean is well established. Numerous observations of large amplitude (both mode-1 and mode-2) solitary waves have facilitated the identification of their unique properties; in particular they contain regions of internal recirculation (trapped cores) that enable mass transport over large distances. However, the basic physics of mode-2 ISWs is as yet not well understood. The present experiments and the associated numerical simulations are focused on providing the first quantitative measure of the extent of mass transported by mode-2 ISWs and insight into the potential effects of mass transport on coastal mixing and the distribution of biochemical material. The ISWs were generated by the release of fluid from an initially mixed volume. It was found that the amplitude and amount of mass transported by the leading and second, following ISW, was proportional to the level of forcing and was attenuated at an approximately uniform rate as the ISW propagated downstream. At the highest level of ISW forcing, over 40% of the mixed fluid was transported within the leading ISW. Excellent agreement was found with the numerical simulations of Salloum, Knio, and Brandt ["Numerical simulation of mass transport in internal solitary waves," Phys. Fluids 24, 016602 (2012)] that were designed to replicate the present experimental configuration. In addition, evidence of a new ISW regime was identified, termed very-large amplitude ISW, which exhibited strong internal recirculation, a smooth front face, and local mixing at the aft end. The present data extend to larger amplitudes than prior studies and exhibit a second order dependence of wave speed and wavelength on amplitude. (C) 2014 AIP Publishing LLC.