Longitudinal average of (panel a; positive values are southward) and (panel b; positive values are prograde), as a function of time and latitude. They were farther smoothed in latitude with a Gaussian of FWHM of 3.6° and in time with a Gaussian of FWHM of 6 months. The black lines show the mean active latitudes. The ticks on the horizontal axis indicate the beginning of each year. The shaded areas indicate the times when the edge effects become visible due to the one-year temporal smoothing of the background flows.