Explain the Factors Affecting the General Atmospheric Circulation (40 Marks)

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  • Topic: Earth, Equator, Hadley cell
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  • Published : October 11, 2012
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Explain the factors affecting the general atmospheric circulation (40 Marks) The variation in heating on the Earth’s surface from the sun is large enough for different patterns of pressure cells to form. With three cells in total, the first being the Hadley cell, devised in 1686 and revised in 1735, Hadley proposed that warm tropical air rises and spreads towards the poles at high altitudes, with a return flow towards the equator at low level. He added in 1735 the effects of the Earth’s rotation, deflecting winds towards the right hemisphere and to the left in the southern hemisphere; this however failed to explain westerly winds in the temperature latitudes. In 1856 Ferrel proposed that three cells form in each hemisphere, resulting in major areas of high and low pressure at the surface. With high pressure forming where the air is falling and low where it’s rising. The three cells; Hadley, Ferrel and Polar cells form the basis of our understanding of global circulation. The two Hadley cells, one in each hemisphere, form the basis of tropical air circulation, and are responsible for the seasonal changes in climate of those regions that experience a wet and dry climate. Each Hadley cell can be divided into four components; between the two cells there is an area of low pressure in equatorial latitudes which is known as the inter-tropical convergence zone or ITCZ. As the sun is always high in the sky, the ground heats rapidly by day and there is a lot of surface evaporation. As the hot air rises in convection currents, an area of low pressure develops. This rising air cools and the water vapour eventually condenses, giving heavy rainfall. At high altitudes the air moves polewards. This air usually circulates as upper westerly winds around the planet as a result of the deflection effect of the rotation of the Earth, known as the Cariolis effect. The net effect though, is for the air still to move polewards. Around 30 N and 30 S the colder air at higher altitudes...
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