The traditional apparatus for rotating-fluid experiments in the laboratory is an annular container of fluid situated on a turntable. A fundamental difficulty in applying to atmospheric circulation problems the knowledge and understanding of the behavior of rotating fluids gained from these expeirments is the geometrical difference between a rotating annulus and a rotating spherical shell. With a view toward identifying features of rotating fluid flow that are dependent on the geometry, we have undertaken rotating annulus-type experiments with a numerical model in spherical coordinates. Rather than construct and test a model specifically for this purpose, we found it expedient to modify an existing general circulation model of the atmosphere be removing the model physics and replacing the lower boundary with a uniform surface. We present here a regime diagram derived from these model experiments, interpret its major features, and contrast these with the major features of rotating annulus regime diagrams. A narrow region where one or two zonal wave numbers are dominant is found within the wave regime. In contrast to the situation in the annulus, there is no upper asymmetric region in our results, and wave activity at low rotation rates appears to be maintained by barotropic rather than baroclinic processes.