Left: pressure vs. latitude stream function of the mean meridional circulation of a planet with Earth’s rotation period. Right: as in the left panel, but for a planet with a rotation period 128 days longer than an Earth sidereal day. As expected for a slowly rotating world, the Hadley cells are now much larger in latitudinal extent, due to the decrease in the strength of the Coriolis force at these slow rotation rates. Note that the color bar limits on the 128 day stream function are a little more than a factor of two larger than the one-day stream function, as one might expect.