Geocentric Science

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Atmospheric circulation is the result of two factors. The first is unequal heating of the Earth’s surface. The second factor is the Earth’s rotation, which causes the Coriolis Effect. Both factors produce prevailing winds and belts of low and high pressure systems from the equator to the poles.

Equatorial regions receive more insolation (solar radiation) throughout the year than polar regions. The air over the equator becomes warm and water evaporates. The equatorial air is warm and moist and forms a low pressure belt. The equatorial air has a low density and rises. As it moves upwards, it expands, cools to its dew point temperature, and precipitation occurs. Cool, dense air moves in to replace the displaced air. This creates a circulation pattern known as a convection cell.

There are three convection cells on either side of the Equator. Warm air rises at the equator (0º) and sinks at 30º North and 30º South. The sinking air mass is dry and forms a high pressure belt (deserts form at this latitude). The air mass at 60º North and 60º South is less dense and rises, and forms a low pressure belt (high amounts of precipitation occur at this latitude). The air mass sinks at 90º North and 90º South and forms a high pressure belt (low amounts of precipitation, and desert conditions occur at this latitude).

Three distinct convection cells form as a result of the Earth’s rotation. If the Earth did not rotate (and if the Earth was composed of uniform material), there would be one convection cell. Air would rise at the equator and sink at the poles. However, since the Earth rotates, one large convection cell is not possible (the convection cell would be extremely unstable and would break down immediately to form three separate cells).

Each convection cell has a prevailing wind system. From 0º to 30º (north and south of the equator), the Trade Winds form, from 30º to 60º (north and south of the equator), the Westerlies form, and from 60º to 90º (north and south of the equator), the Polar Easterlies form. These wind systems move as a result of the Coriolis effect (sinking and rising air is deflected to the right in the Northern Hemisphere and is deflected to the left in the Southern Hemisphere).