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This plot, which depicts the average potential temperature in the atmosphere in January demonstrates the warmer temperature observed near the equator, and colder temperatures observed near the poles. The center of the warmer temperatures appears to the south of the equator, due to the southern position of the sun in January. Likewise, cooler temperatures are observed over the North Pole rather than the South Pole. What is particularly notable about this plot is that the potential temperature is actually cooler in the stratosphere over the tropics than it is over the poles, indicating that the higher altitudes are warmed over the poles, where the lower altitudes are warmed near the surface. The gradient of the potential temperature is clearly visible over the mid-latitudes, but is essentially non-existent over the tropics, indicating thorough mixing of the air in the tropical region in which the Hadley cell dominates.
The warm temperature over the tropics translates to rising motion, which may be determined from the average value of ω, the vertical movement of the air, as averaged over all longitudes.
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Easterly winds are clearly evident at the surface, ranging up to nearly 10 m/s about the 900 mb level. The westerly winds aloft are less visible, due to the dominant westerly flow of the jet stream north of the 30th parallel. Even so, a slight extension of weak westerly winds may be observed to extend down nearly to the equator, which is suggestive of the westerly contribution of the top part of the Hadley cell.
Tank
It is possible to visualize the movement of the Hadley cell in a rotating tank of water to verify the expected "winding" and "unwinding" of the Hadley cell. A temperature gradient may be created in a slowly rotating tank of water (< 1 rpm) by placing a container of ice in the middle of a rotating tank of water. Water will then cool next to the tank, sinking and slowly flowing outwards. Continuity will then ensure that warm water on the outside of the tank ..will flow inward to replace the cool, sinking water. As it moves inward, the warmer surface water should move in the direction of the rotation of the tank of water.