This animation (produced by Tim Merlis) shows the spinup of a macroturbulent circulation from an axisymmetric circulation. The upper panel shows zonal-mean zonal wind and the lower panel shows surface air temperature, with the zonal mean in the small white panel on the right.

In the macroturbulent simulation, there is no subgrid-scale diffusion of heat or momentum above the planetary boundary layer. Vertical subgrid-scale diffusion of heat and momentum is necessary for stability in the axisymmetric simulations. Because the subgrid-scale diffusion is turned off when the three-dimensional perturbation is added to the axisymmetric circulation, the Hadley circulation first weakens before it strengthens when large-scale eddies form. (See Schneider (2006) for a description of the simulation.)

Schneider, T., 2006: The general circulation of the atmosphere. Annual Reviews of Earth and Planetary Sciences, 34, 655-688.
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