Abstract

The experiment reported in this paper was designed to study the effect of large mountain-barriers on zonal currents in the atmosphere. Obstacles of various sizes and shapes are moved zonally in a rotating spherical shell of liquid, and observations are made of the resulting perturbed flow. Striking differences occur, depending on the direction of relative rotation of the barrier. If the flow is westerly with respect to the obstacle (in the direction of the basic rotation), a strong anticyclonic circulation develops around it and this sets up planetary waves around the globe. The wave number is found to correspond very closely to a frequency equation derived from the vorticity equation.

If the flow is easterly relative to the obstacle, a similar anticyclonic circulation arises, but is confined to the immediate vicinity of the barrier. No long waves occur but, if the motion is viewed with respect to the spherical bowls, the obstacle, moving eastward, drags a strong westerly jet with it in its latitude band.

A study was also made of the flow over a barrier which is not as high as the “atmosphere.” This reveals a strong anticyclonic turning of the fluid as it moves over the obstacle, and a tendency for this to combine with the anticyclonic circulation in the westerly case to produce a trough immediately downstream.

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