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In the tropics, the Coriolis parameter is relatively small and the influence of Earth’s rotation is weak. In this regime, the Hadley circulation prevails, transporting energy from the equator to a latitude of roughly 30N. As air over the equator warms, it begins to rise rise into the upper atmosphere. It than diverges poleward, acquiring angular momentum as it travels to higher latitudes. At the edge of the Hadley cell (30N) the air sinks to surface and begins to travel towards the equator again. Evidence of the Hadley circulation can be observed in the following NCEP reanalysis plots. The plots can be found at: http://www.esrl.noaa.gov/psd/cgi-bin/data/composites/printpage.pl
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