Global Atmospheric Circulation

The sun’s energy does not fall evenly onto our spherical planet: some parts of the earth (a on image 1) are pointing directly at the sun, therefore the sun’s energy has less distance to travel to reach the surface and is focused over a small surface area; whereas other parts (b on image 1) point away from the sun, therefore the same amount of sunlight has further to travel (which allows more solar energy to be deflected back into space by particles in the atmosphere) and is spread over a larger region. The amount of solar energy an area gets over a period of time is known as insolation.