Global atmospheric circulation is a worldwide system of winds, which transports heat from tropical to polar latitudes. In each hemisphere, air circulatesin cells.
The Basics
Hot air rises (think of a hot air balloon)
Rising air causes low pressure
Low pressure draws moisture from the ground creating clouds, rain and storms.
Cold air sinks
Sinking air presses on the Earth's surface, causing high pressure
High pressure often brings fine weather.
Wind is caused by air moving from high atmospheric pressure to low atmospheric pressure. Winds blowing towards the equator are called trade winds.
Global Atmospheric Circulation
Winds are movements of air caused by differences in air pressure. They move FROM areas of high pressure TO areas of low pressure.
Winds are part of global atmospheric circulation loops called cells. There are three cells in each hemisphere: 1. Hadley Cell 2. Ferrel Cell 3. Polar Cell
Hadley Cell
The heat of the sun at the equator causes air to rise. This creates a low pressure belt. Huge rain clouds are formed. Ecosystems such as tropical rainforests form here.
The air continues upwards until it cannot rise any further.
The air will then move towards the Poles at a high altitude.
As the air makes its way towards the Poles it becomes cooler.
As the air cools, it sink down towards the earth at about 30 degrees. This creates a high pressure belt with very low rainfall. Ecosystems such as deserts form here.
As it reaches the earth some of the air will move back towards the equator forming the first cell called the Hadley cell. Surface winds blowing towards the equator are called trade winds.
Some air will also move towards the poles.
Polar Cell
At the Poles air is sinking due to the low temperature.
This air will then move towards the equator at a low level.
At about 60 degrees this air will meet warmer air moving towards the poles from the equator.
The air will rise upward until it reaches the top of the atmosphere where the air will move in two directions.
Some air will head back to the poles as surface winds forming the polar cell.
Ferrel Cell
Some air from the Polar cell moves back to the equator meeting the Hadley cell. This forms the middle cell called the Ferrel cell.
Watch the video below to recap on what we learnt during the lesson:
Revision links The below video contains a great explanation of the difference between high and low air pressure www.bbc.co.uk/education/clips/zv46n39