Tutorial 2.3
QBO: Experimental results
Here we show some filmed sequences from Alan Plumb and Angus McEwan's original experiment (Plumb & McEwan 1978). The clips were recorded in April 1978 and originated from CSIRO, an Australian government agency responsible for scientific research.
The sequences were viewed through a window in the side of the apparatus, and the field of view covers one complete wavelength of the forcing. The counter on the lower right shows the time in seconds.
- Forcing frequency: \(w=0.41\text{ s}^{-1}\)
- Forcing amplitude: \(e=6.4\text{ mm}\)
- Forcing wavenumber: \(m=8\)
- Fluid depth: \(D=0.41\text{ m}\)
- Buoyancy frequency: \(N=0.86\text{ s}^{-1}\)
Remarks: The forcing here is too weak – the wave is stable, thus there is no mean flow. Motion is speeded up about 30 times (in film) when shown at 16 frames per second.
- Forcing frequency: \(w=0.43\text{ s}^{-1}\)
- Forcing amplitude: \(e=8.0\text{ mm}\)
- Forcing wavenumber: \(m=8\)
- Fluid depth: \(D=0.44\text{ m}\)
- Buoyancy frequency: \(N=1.57\text{ s}^{-1}\)
Remarks: The forcing here is stronger – the wave is unstable; thus a mean flow is generated and begins to oscillate. Motion is speeded up about 100 times.
- Forcing frequency: \(w=0.31\text{ s}^{-1}\)
- Forcing amplitude: \(e=11.0\text{ mm}\)
- Forcing wavenumber: \(m=8\)
- Fluid depth: \(D=0.41\text{ m}\)
- Buoyancy frequency: \(N=1.40\text{ s}^{-1}\)
Remarks: The forcing here is stronger still – the mean flow oscillates more rapidly and vigorously. The motion is speeded up about 100 times.