Intrusions, Waves and Solitary Waves

Bruce R. Sutherland
Dept. Mathematical and Statistical Sciences
University of Alberta

Tuesday, Dec 7, 1PM ECOT 226

The dynamics by which mixed fluid collapses and intrudes into the density-stratified ambient is not well understood. As a starting point in examining these dynamics, in particular of an intrusion propagating along a 2-layer fluid interface such as an atmospheric inversion or the oceanic thermocline, we have performed a series of laboratory experiments and compared their results with existing theory.

For an intrusion released in a long rectangular tank, we may compare its predicted steady-state speed (Holyer & Huppert 1980, Sutherland et al 2004) with measurements. Though good in symmetric circumstances, the theory otherwise predicts qualitatively incorrect behaviour. This is because it neglects the possibility that the intrusion might generate internal and solitary waves, which clearly are seen in experiments.

For an intrusion released from a cylinder, self-similarity theory predicts it should decelerate as it spreads radially. However, laboratory experiments reveal this is not the case: intrusions instead travel at constant radial speed. Even when Coriolis forces are introduced, experiments reveal that intrusions still propagate at constant speed. Rotational effects act only to limit the radial distance to which the current travels.