ABSTRACT
Our modern conceptual models of monsoons and cross-equatorial Hadley cells all hark back to the dry, axisymmetric, nearly inviscid theory of angular momentum conserving meridional overturning circulations popularized by Held and Hou 1980. However, misunderstanding of this theory and its subsequent extensions abounds, and recent studies of slowly rotating planets call its utility into question for global-scale circulations. I present a synthesis of the existing forms of axisymmetric, nearly inviscid theory, emphasizing the distinctions between its predictions for overturning cell emergence vs. extent, clarifying the links between the original dry, zonally symmetric formulation with the modern moist framework for zonally confined monsoons, and presenting new physical insights that they provide. Using dry dynamical core simulations, I show how to generate a cross-equatorial Hadley cell on Earth that spans from pole-to-pole based on the arguments of axisymmetric theory. Before all that, I show how to build a rotating tank platform for GFD demonstrations using Lego bricks.