Convection in a rotating annulus with a negative radial temperature gradient

The transition from the flow in the wave regime of the rotating annulus to the flow in the upper symmetric regime has been investigated experimentally in two apparatus with positive as well as negative radial temperature gradients. It has been found that the absolute value of the radial temperature difference at which the transition occurs depends on the sign of the temperature gradient. The velocities of the wave patterns relative to the rotating annulus have also been measured, with positive and negative temperature gradients and four different rotation rates, with the fluid being in contact with a rigid lid. Repeated changes in the direction in which the patterns move have been observed, at different values of the negative radial temperature gradient. Abrupt increases of the pattern velocities occurred with the transition from 2 waves to 1 wave, when the temperature gradient was either positive or negative.