Insensitivity of the zonally and temporally averaged zonal wind (ms^-1) to the different modelling choices. The simulations in the left panels use the “shallow” and the right panels the “full” equation set. The top left panel shows a simulations where diffusion is applied to θ in addition to u and v. The top right panel shows a simulations with non-uniform vertical level placement to optimise sampling of the local scaleheight. The bottom left panel shows the results when the atmospheric height is decreased from H = 1.1 × 10⁷ m to H = 6.7 × 10⁶ m, and the bottom right panel when it is increased to 1.25 × 10⁷ m (although only the overlapping pressure domain of these simulations with that of the models in Heng et al. (2011), shown in Fig. 4, is displayed to aid comparison).