VISCOUS EFFECTS IN INTERNAL WAVES OF 2-LAYERED FLUIDS WITH VARIABLE DEPTH

Experiments are described that have been performed in a 10 m long, 0.3 3 m wide channel on the baroclinic wave propagation ina two-layered fr ee surface fluid system with an upper fresh-water and a lower saltwate r layer. The total water depth is varied between 10 and 20 cm and laye r ratios 3:1, 2:1, 1:3 are experimentally studied with a density anoma ly of S=2.2%. A wave generator produces nearly exactly soliton-type wa ve signals at the fresh-water sail-water interface. These signals prop agate along the channel and are recorded at six equidistant positions with electrical resistivity gauges. The damping can be measured by the attenuation of the wave amplitude and that of the potential energy. I t is shown that the dominant dependence of the damping coefficient is nearly proportional to the inverse of the water depth. A second depend ence is proportional to the inverse of the channel width, but a clear correlation with the layer ratio, even though it is discernible, could not be found. With this depth dependence incorporated in the non-line ar dispersive wave equations a comparison of computationally predicted interface-displacement-time series with their measured counterparts w as performed for a two-layer-fluid channel whose depth changes from a deep region via a ramp to a shelf region (plateau). For ratios of the plateau height to the lower level depth (i.e., degrees of blocking) le ss than 0.85 agreement is excellent. At higher degrees of blocking the ramp geometry induces local eddies that make that theoretical model i nvalid.