In modelling atmospheric flows the baroclinic instability of the flow in a differentially heated rotating annulus plays a central role. This paper deals with an experimental study using LDV and flow visualization techniques. Usually the temperature difference, AT, was kept fixed while the angular velocity, co, was varied. On crossing the stability boundary, the primary bifurcation, the basic flow gives way to a baroclinic wave flow. For a given annulus geometry the wave number, m, of the first wave pattern was found to be uniquely defined by A T. The measured critical values of co, (J)crit, agree reasonably well with those obtained by other authors. On increasing co above 03crit the wave number changed, this process showing hysteresis. The situation might indicate secondary bifurcation phenomena. Flow visualization using aluminium particles shows surface flow details.
experimental study in which we determined critical values of 09, while keeping A T fixed.
2 Apparatus
In order to have full optical access to the annular domain of our apparatus, the outer cylinder was made from a precision-bore glass-tube which had an inner radius of r 2 = 74.80 _+0.05 mm. The inner cylinder, which had a radius of r1= 47.70 _+ 0.05 mm, was machined from brass. Thus the radius ratio rl=rl/r z is 0.638 and the gap width d=r2-r x was 27.1 mm. The total length of the working section, l, was