University of Alberta
Edmonton, Alberta, Canada
The Morning Glory, a naturally occurring atmospheric disturbance viewed over North-Eastern Australia, is believed to be an example of a large-amplitude solitary wave. When not made visible by clouds, strong wind shear associated with the wave can be hazardous for aircraft. The dynamics governing the genesis, evolution and decay of Morning Glory is not fully understood. Through mathematical analysis aided by laboratory experiments, we hope to better understand the life-cycle of this phenomenon. We perform a series of lock-release experiments in which we examine the behaviour of the flow within a three-layer, salt-stratified fluid. At a certain interfacial thickness in the stratified fluid, a gravity current excites an internal double-humped solitary wave, which appears in the interfacial layer in front of the gravity current head. When this occurs, the gravity current itself stops propagating, and trailing it are large amplitude trapped internal waves. We measure the speed of propagation and the amplitude of the internal waves, and study the effect of interface thickness and density difference to determine for what critical parameters a solitary wave is generated. We propose that this transition occurs because the gravity current resonantly couples with trapped internal waves for a sufficiently thick interface.