Internal solitary waves in a structured thermocline with implications for resuspension and the formation of thin particle-laden layers

A structured thermocline model is employed to elucidate the role of environmental factors in the characteristics of internal solitary waves, including the related implications for wave-induced resuspension and the formation of thin layers with enhanced concentration of passive particles. The model considers varying relative strengths between a thin seasonal thermocline and a broad permanent thermocline together with a sheared current in the upper mixed layer. The influence of these environmental factors on the stimulus of the benthic boundary layer under the footprint of solitary waves is assessed, particularly the potential for inducing boundary layer separation and lowering the near-bottom Richardson number. Also, the flow field associated with an internal solitary wave is shown not only to transport particles horizontally, but to create a tendency for passive particles located in the mixed layer to migrate Vertically and concentrate in a thin layer. This latter effect is especially pronounced for particles that are heavier than the host fluid and have particle Reynolds numbers of order unity or greater. Although specific calculations for bubbles have not been included here, the net vertical displacement for light particles following the passage of a solitary wave may be quite large.