Gravity Currents and Internal Gravity Waves

The image shows a gravity current (dyed in red) propagating along an interface between fresh water (above) and salt water (below).

If the interface is sufficiently wide, the gravity current collapses and trapped internal gravity waves are excited (wavy red tail). Ahead of the current a solitary wave is generated.

Similarly, solitary waves are generated by intrusions in two-layer fluid when the upper and lower fluid depths are not equal.

Characterising where this transition occurs is important, for example, in understanding how far pollutants may be transported in the atmosphere, oceans, or lakes.

You can see intrusions and the transition to waves in the five movie files below.

In each experiment, the tank is approximately 2m long and 18cm wide. Fluid is released from a lock of length 18cm.

Data are given in terms of the bottom fluid density (rhob), top fluid density (rhot) and lock fluid density (rhol). The depths of the top and bottom layers are Ht and Hb, respectively.

Each image below is a snapshot taken 6 seconds after the gate is extracted. Click on the image to view an mpeg movie of the entire experiment.

Image after 6 seconds	Experiment Description	parameters
	Bottom propagating gravity current	(rhol-rhob)/rhob = 0.02 Hb=10cm
	Intrusion in two layer fluid: Symmetric case	(rhol-rhob)/rhob = (rhot-rhol)/rhot = 0.01 Hb=Ht=10cm
	Intrusion in two layer fluid: Asymmetric case 1	(rhol-rhob)/rhob = 0.015, (rhot-rhol)/rhot = 0.005 Hb=Ht=10cm
	Intrusion in two layer fluid: Asymmetric case 2	(rhol-rhob)/rhob = 0.0175, (rhot-rhol)/rhot = 0.0025 Hb=2.5cm, Ht=17.5cm
	Intrusion in two layer fluid: Asymmetric case 3	(rhol-rhob)/rhob = 0.015, (rhot-rhol)/rhot = 0.005 Hb=2.5cm, Ht=17.5cm
Experiments performed by Patrick Kyba, Dept. Math. and Stat. Sciences, U. Alberta, 2002

Department of Physics

Department of Earth and Atmospheric Sciences