Atmospheric Circulation

The Earth and its atmosphere are both controlled primarily by the Sun and they make up an interconnected global system. Different climatic areas are the result of atmospheric movements (see the tricellular model below) within this global system. The cause of these atmospheric movements is the difference in temperature between equatorial regions and polar regions, this is caused by distance from the sun and the amount of atmosphere to travel through.

It is the energy flows in the atmosphere that cause the variations in our weather

The Tricellular Model

The tricellular model is made up of three different air masses, these control atmospheric movements and the redistribution of heat energy. The three air masses, starting from the equator, are called the Hadley cell, Ferrel cell and the polar cell.

The tricellular model also contains the ITCZ (Inter-tropical convergence zone), this is the meeting place of the trade winds from both the northern hemisphere and the southern hemisphere. The ITCZ is a low pressure area where the trade winds, which have picked up latent heat as they crossed oceans, are now forced to rise by convection currents. These rising convection currents are then cooled adiabatically to form massive cumulonimbus clouds.

As seen in the diagram this rising air at the ITCZ leads to a circular movement caused by the cooling of the air and the Coriolis effect, this leads to the formation of the first air mass, called the Hadley cell and named after its discoverer.

The Jet Streams & Rossby Waves

Between the different atmospheric cells high up in the tropopause at a height of about 5 miles are the jet streams, named the polar jet stream (40-60°N+S) and the subtropical jet stream (25-30°N+S). These jet streams move air at a high speed (up to 130mph) around the Earth horizontally and give rise to Rossby waves. The jet streams were first discovered when Zeppelins were blown off course in WW1.

Rossby waves were discovered by Carl-Gustaf Rossby, a Swedish meteorologist, in the 1930’s. They are waves or zigzags in the jet streams as the travel around the Earth. The number of waves varies throughout the year but usually in summer it’s between four and six while in winter it’s three.

Jet streams have also been known to influence flights, for example it’s quicker to travel by aeroplane from London to New York then it is the other way around because the altitude planes travel at is similar to these high speed winds.

Primarily Written by: Edd TurtleLast Modified: December 19, 2011