<P> The Hadley system provides an example of a thermally direct circulation . The thermodynamic efficiency of the Hadley system, considered as a heat engine, has been relatively constant over the 1979--2010 period, averaging 2.6% . Over the same interval, the power generated by the Hadley regime has risen at an average rate of about 0.54 TW per year; this reflects an increase in energy input to the system consistent with the observed increasing of tropical sea surface temperatures . </P> <P> Overall, mean meridional circulation cells such as the Hadley circulation are not particularly efficient at reducing the equator - to - pole temperature gradient due to cancellation between transports of different types of energy . In the Hadley cell, both sensible and latent heat are transported equatorward near the surface, while potential energy is transported above in the opposite direction, poleward . The resulting net poleward transport is only about 10% of this potential energy transport . This is partly a result of the strong constraints imposed on atmospheric motions by the conservation of angular momentum . </P> <P> In the early 18th century, George Hadley, an English lawyer and amateur meteorologist, was dissatisfied with the theory that the astronomer Edmond Halley had proposed for explaining the trade winds . What was no doubt correct in Halley's theory was that solar heating creates upward motion of equatorial air, and air mass from neighboring latitudes must flow in to replace the risen air mass . But for the westward component of the trade winds Halley had proposed that in moving across the sky the Sun heats the air mass differently over the course of the day . Hadley was not satisfied with that part of Halley's theory and rightly so . Hadley was the first to recognize that Earth's rotation plays a role in the direction taken by an air mass as it moves relative to the Earth . Hadley's theory, published in 1735, remained unknown, but it was rediscovered independently several times . Among the re-discoverers was John Dalton, who later learned of Hadley's priority . Over time the mechanism proposed by Hadley became accepted, and over time his name was increasingly attached to it . By the end of the 19th century it was shown that Hadley's theory was deficient in several respects . One of the first who accounted for the dynamics correctly was William Ferrel . It took many decades for the correct theory to become accepted, and even today Hadley's theory can still be encountered occasionally, particularly in popular books and websites . Hadley's theory was the generally accepted theory long enough to make his name become universally attached to the circulation pattern in the tropical atmosphere . In 1980 Isaac Held and Arthur Hou developed the Held - Hou Model to describe the Hadley circulation . </P> <P> The region in which the equatorward moving air masses converge and rise, is known as the intertropical convergence zone, or ITCZ . Within that zone develops a band of thunderstorms that produce high - precipitation . </P>

What type of uplift of air is associated with hadley cells