Explaining the scope of Earth's tropical air flows

In a Hadley cell, air rises from near the equator at the surface to the upper troposphere, moves poleward until about 30 degrees in latitude, then descends into the subtropics before moving equatorward along the Earth's surface.

Recent observations and simulations with climate models suggest that the north-south extent of the Hadley cells may be increasing, which may dramatically alter climate on regional scales. Korty and Schneider analyze dynamical mechanisms responsible for terminating the Hadley cells in the subtropics.

They suggest that Hadley cells terminate where eddies generated in the extratropics become so deep that they reach the upper troposphere. At the latitude where this occurs, the direction of the momentum flux carried by the eddies changes sign; the tropical Hadley cells give way to the extratropical Ferrel cells.

The authors show how the atmospheric thermal structure determines this latitude in dry atmospheres. It remains to be investigated how latent heat release in phase changes of water influences the Hadley cell termination.-American Geophysical Union