The Held–Hou Model is a model for the

Hadley circulation The Hadley cell, also known as the Hadley circulation, is a global-scale tropical atmospheric circulation that features air rising near the equator, flowing poleward near the tropopause at a height of above the Earth's surface, cooling and des ...

of the atmosphere that would exist in the absence of atmospheric turbulence. The model was developed by

Isaac Held Isaac Meyer Held (born October 23, 1948) is an American meteorologist. He is a retired senior research scientist at the Geophysical Fluid Dynamics Laboratory. Held was elected to the United States National Academy of Sciences in 2003. Biography ...

and Arthur Hou in 1980. The essence of the model is that air rising from the surface at the equator conserves its

angular momentum Angular momentum (sometimes called moment of momentum or rotational momentum) is the rotational analog of Momentum, linear momentum. It is an important physical quantity because it is a Conservation law, conserved quantity – the total ang ...

as it moves poleward. This distribution of wind, in turn, determines the distribution of temperature, which determines the latitudinal extent of the circulation by requiring

energy conservation Energy conservation is the effort to reduce wasteful energy consumption by using fewer energy services. This can be done by using energy more effectively (using less and better sources of energy for continuous service) or changing one's behavi ...

. This stands in contrast to

George Hadley George Hadley (12 February 1685 – 28 June 1768) was an English lawyer and amateur meteorologist who proposed the atmospheric mechanism by which the trade winds are sustained, which is now named in his honour as Hadley circulation. As a key ...

's original conception of the circulation, which he argued reached the poles. The Hadley circulation has a cooling effect at and near the

equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

and a warming effect at higher

latitude In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...

s within the

Hadley cell The Hadley cell, also known as the Hadley circulation, is a global-scale tropical atmospheric circulation that features air rising near the equator, flowing poleward near the tropopause at a height of above the Earth's surface, cooling and des ...

. This energy transport can be converted into a mass transport, to determine the strength of the circulation, by normalizing by the appropriate vertical stability. The effects of

moisture Moisture is the presence of a liquid, especially water, often in trace amounts. Moisture is defined as water in the adsorbed or absorbed phase. Small amounts of water may be found, for example, in the air (humidity), in foods, and in some comme ...

and

seasons A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's axial tilt, tilted orbit around the Sun. In temperat ...

on the model have been studied. Earth's atmosphere violates the underlying assumptions of the model: angular momentum is not conserved and the tropical atmosphere is not energetically closed. As such, the Held–Hou model is a conceptual model that does not make quantitatively accurate predictions of the sensitivity of the Hadley circulation to changes in atmospheric parameters.

References

Tropical meteorology {{Meteorology-stub