Three Cell Model

Winds

All of our planet's energy ultimately comes from the Sun which radiates 10¹⁸ watts to the Earth each hour. About 1 or 2% of this is converted to wind energy, about 100 times more than is used by plants. Equatorial regions are heated by the Sun more than the rest of the globe is. Hot air is lighter than cold air and so rises and spreads outwards to the North and South Poles. The Coriolis Force is the diversion of winds to the right in the northern hemisphere and to the left in the southern hemisphere and is caused by the Earth's rotation.

The Three Cell Model

The Three Cell Model of wind movement models the behaviour of winds on earth. As hot air from the Equatorial regions moves outwards, the Coriolis Force prevents it from moving past 30^o latitude. At 30^o North and South, therefore, there are high pressure zones where the air begins to sink down again. As the wind rises from the equator there will be a low pressure area and where cold air exists at the Poles there is high pressure. This results in the formation of three cells. The Hadley Cell consists of hot air rising at the equator and then moving outwards cooling and sinking at 30^o and correspondingly, cold air moving low down towards the equator. The Ferrel Cell consists of cold air sinking at 30^o and then moving outwards low down towards 60^o and correspondingly, warmer air rising at 60^o, cooling and moving towards 60^o. The Polar Cell is much the same with cold air sinking at the Poles and warmer air rising at 60⁰. There is obviously interaction between the cells but this is a grossly simplified model.

For diagrams of the Three Cell Model go to: http://apollo.lsc.vsc.edu/classes/met130/notes/chapter11/three_cell.html