Illustration of the development of shear in 2D simulaitons. Top: velocity map from a 2D simulation illustrating the transition to shear. The quivers indicate the velocity direction and magnitude. There are two distinct regions of oppositely directed flow separated by a transition of approximately equal width. Bottom: time series of and showing the decay of the vertical component and the growth and saturation of the horizontal component. After a sufficient length of time (twice that of the 3D simulations), steady state has been reached and any convective motion is suppressed in favour of shear.