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Figures 5 and 6 are of the zonally average meridional wind in January and July respectively. Meridional wind is measured from north to south. Positive numbers represent northward motion. In Figure 5, the greatest winds are observed in the Northern Hemisphere, while it is experiencing a winter. Similarly, in Figure 6, the greatest winds are in the Southern Hemisphere.
As particles move pole-ward in the upper atmosphere, they get deflected (right in the Northern Hemisphere and left in the Southern). As discussed previously, particles gain zonal speed upon moving pole-ward. Figures 7 and 8 are of this zonal wind speed. The figures also show the trade winds between the equator and 30°, from the return flow at the surface being deflected westward as a result of the Coriolis force.
From the thermal wind relation, the greatest wind speeds are associated with the largest temperature gradient. In Figures 9 and 10, the steepest slopes are on the winter hemisphere. In July, there is a much larger difference between the zonal wind speeds of the two hemispheres than in January. This difference is likewise apparent in the July potential temperature data, for which the slope is very clearly steeper on one side.
The two key characteristics of the Hadley cell (from the equator to about 30°) are that there is large-scale overturning circulation, and that wind speeds increase in the pole-ward direction. The next goal was to simulate this in a laboratory environment to study the heat transport associated with Hadley circulation.
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