1) At the equator the sun warms the Earth, which transfers heat to the air above, causing it to rise. This creates a low pressure belt with rising air, clouds and rain
2) As the air rises it cools and moves out to 30 degrees north and south of the equator.
3) 30 degrees north and south of the equator the cool air sinks, creating a high pressure belt with cloudless skies and very low rainfall
4)The cool air reaches the ground surface and moves as surface winds either back to the equator or towards the poles - surface winds blowing towards the equator are called trade winds - surface winds blown towards the poles are called westerlies.
5) 60 degrees north and south of the equator the warmer surface winds meet colder air from the poles. The warmer air is less dense than the cold air so it rises, creating low pressure
6) Some of the air moves back towards the equator , and the rest moves towards the poles
7) At the poles the cool air sinks, creating high pressure. The high pressure air is drawn back towards the equator as surface winds