CIRCULATION OF THE ATMOSPHERE Under the influence of pressure differences resulting from solar heating, and of friction between wind and the rotating earth, a general pattern of atmospheric circulation is set up. The surface winds shown in atlases are the ground-level part of a three-dimensional system that has not yet been well explored. The pattern still being worked out shows a complex circulation, with air over the Equator ascending and flowing discontinuously to the poles, which are themselves regions of generally subsiding air (Palmen, 1951). Across the Equator there is relatively little interchange between northern and southern hemispheres.