Rotating Gravity Currents on a Slope

The image shows a gravity current (dyed in blue) propagating along the conical bottom of a tank which is rotating. The experiment simulates the propagation of dense bottom ocean currents on the sloping margins of the continental shelves. The rotating tank simulates the effects of the Earth's rotation.

The current is unstable and breaks into vortices for a wide range of parameters. Here we compare the dynamics of the instability for an axisymmetric gravity current (injected from below through a circular ring) and for a gravity current with a front (injected through a semicircular ring).

In both experiments:

• the tank has radius 45 cm and the conical bottom has a slope of gradient of 1/15
• The tank is filled with fresh water to a depth of 15 cm and rotates at 1 radian/second.
• Fluid is injected through a thin gap in the bottom which forms a ring of radius 15 cm.
• The injected blue-dyed fluid is salt water which is 0.15% more dense than the ambient fresh water in the tank.

In the full-circle experiment, fluid is injected for 30 seconds and in the half-circle experiment, fluid is injected for 20 seconds.

• In both cases the current is approximately 1/3 the total fluid depth at the end of the injection time.

Each image below is a snapshot taken during the course of an experiment from above and from the side of the tank.

Gravity current injected from a circular ring	Gravity current injected from a semicircular ring
Experiments performed by Joshua Nault and Kerianne Yewchuk, Dept. Math. and Stat. Sciences, U. Alberta, 2002

Department of Physics

Department of Earth and Atmospheric Sciences