VERTICAL LENGTH SCALE OF DOUBLE-DIFFUSIVE INTRUSIONS

A laboratory model has been developed to stimulate the mixing at an oceanic front across which there are large T-S anomalies but a small net horizontal density difference. Identical stable density distributions are established on the two sides of a central vertical barrier, using the analogue system of salt solution at one end of a tank and sugar solution at the other. When the barrier is removed, local density anomalies are produced by double-diffusive transports across the frontal region. These lead to the spontaneous formation of interleaving layers over the whole depth of the tank, with a scale directly proportional to the horizontal concentration differences across the front and inversely proportional to the vertical density gradient. This result is explained using a theoretical argument based on a comparison of the potential energy in the initial and final distributions and the mechanism of energy release by double-diffusive transports across the interfaces between alternate layers. The available data on the scale of intrusive layers near oceanic fronts are also broadly consistent with this energy argument. © 1979.