1. THE 3 CELL MODEL

2. Tropical areas receive more insolation (energy from the sun) than the polar regions.
There is an energy surplus at the Tropics and an energy…

3. In theory this would result in the Tropical regions getting…and the Polar regions getting…
In reality, energy is transferred …
One of the ways in which this happens is by atmospheric circulation.

4. The Single Cell Model
The single cell model was proposed in 1735 by George Hadley. It suggests that:
Air at the Equator is heated up causing it to …,creating a belt of …
The warm air moves towards the poles where it…,creating a belt of…
Surface winds always blow…
This completes the Hadley Cell.
In this way, surplus energy from the Equator is transferred polewards.

5. The Three-Cell Model
Later observations proved that Hadley cells exist but only extend as far as 30°N and 30°S of the Equator. This is because the air warm air… before it reaches the Poles.
In reality there are actually three cells –the Hadley cell…

6. The Hadley Cell The Hadley cell extends from the equator to…
Air at the equator is heated up.
Warm air rises creating a zone of…
Warm air moves polewards but begins to…
The cold air sinks at… creating a zone of…
The cold air then flows back towards the equator because surface winds always blow from…

7. The Polar Cell
At the Poles, air is being cooled. Cold air is dense and therefore…
The descending cold air moves towards the lower, warmer latitudes.
As it moves towards the lower latitudes it becomes warmer and therefore … at… creating a zone of …
The rising warm air then moves polewards completing the Polar cell.

8. The Ferrel Cell The Ferrel cell lies in between the other two cells.
The Hadley cells and Polar cells are said to thermally … cells because they are driven by …
The Ferrel cell is a thermally… cell because it is driven by friction between the other two cells

9. The Ferrel Cell
As the air in the Hadley Cell… at about 30ºN and 30ºS, it pulls the air beside it… as well, due to…
As air in the Polar Cell… at about 60ºN and 60ºS, it pulls the air beside it… as well.
In this way… air is transferred from the … cell to the … cell via the Ferrel cell for cooling.
And cold air is transferred from the Polar cell to the Hadley cell via the … for …

10. Global Wind Circulation
Complete the diagram on the next slide by filling in the blanks in the text boxes to show the names of the pressure belts and associated winds.
Draw arrows on the diagram to show the wind direction.
Remember winds blow from high to low pressure and winds are deflected to the right in the northern hemisphere and to the left in the southern hemisphere due to the Coriolis Effect.

11. Polar High Pressure Polar Easterlies Sub-Polar… Sub-Tropical…
Mid Latitude…
Sub-Tropical…
North East…
Equatorial…