Experiments to study the beta-effect in atmospheric dynamics

In atmospheric dynamics, it is well known that the beta-effect, namely, the variation of Coriolis force with latitude causes the mid-latitude large-scale tropospheric waves such as the westerlies to propagate vertically into the stratosphere. Although this has been well proved in the theoretical works and atmospheric observations, to test this also in a laboratory we demonstrate here rotating fluid annulus experiments setting a conical bottom in a tank to create an equivalent beta-effect. Three clear evidences of the beta-effect were observed in the wavenumber-2 flow: the wave flow propagated vertically, its critical level rose, and its drift velocity reduced. Then the quasi-geostrophic potential vorticity equation succeeded in describing this phenomenon below a height slightly lower than the critical level, but failed near that level.