The atmospheric circulation of a planet that has no zonal asymmetries in boundary conditions will remain axisymmetric if the initial condition is. So we can calculate the “ideal” Hadley circulation that would result in that case by choosing an axisymmetric initial condition in an idealized GCM without zonal inhomogeneities in boundary conditions. However, for an Earth-like planet, the resulting axisymmetric circulation is unstable with respect to non-axisymmetric perturbations.