grade 11

1. GLOBAL AIR CIRCULATION
ATMOSPHERIC PRESSURE

2. Unequal heating and global air circulation
Energy from the sun does not reach the earths surface evenly, it is
hotter on the equator and less energy reaches the poles
The difference in the temperature leads to
In the atmospheric pressure causing air to
Move both vertically and horizontally
Forming global air circulation

3. INCOMING SOLAR RADIATION

4. World pressure belt
• In places of higher temperatures, air expands and rises to form an
area of low pressure.
• Air is drawn towards a low pressure area replacing rising air from an
area of converging air
• Low temperatures cause air to contract and descend forming high
pressure areas, descending air moves outwards causing divergence

5. Identify the cells, pressure and trophics

6. The hadely cells
Occurs between the equator and 30 degrees N and S
Here occurs an equatorial low caused by rapid uplift of hot, moist air
resulting in very low pressure at the surface
Rising air reaches dew point
Dew point the temperature at which water vapour starts to
condense
CONDENSATION>>>>>>>CUMULINOMBUS CLOUDS FORMING>>>>>
THUNDERSTORMS AND CONVECTION RAIN FALL
Divergence at 10 000 metres about surface cause high pressure at
subtropics as it descends creating warm dry weather ( subtropical
high)

7. Easterly winds
easterly wind drawn into the equatorial low from subtropical high
these are surface winds of the Hadley cell
Intertropical convergence zone ITCZ
The zone where two sets of tropical easterlies converge
Causing frequent thunderstorms

8. The ferrel cell
Occur between 30 degrees N and S also 60 degrees N and S
Westerly winds blow subtropical high pressure belt towards the
subpolar low pressure belt
Ferrel cell on the surface experiences westerly winds
In the S hemisphere westerlies blow NW
In the N hemisphere westerlies blow SW

9. Polar cells
Occur between poles and 60 degrees north and south
Winds converge along polar fronts
Zones where two air masses of different temperatures meet is called
a front
The front between the cold and warm air masses which meet at 60
degrees N and S

10. Atmospheric temperature, pressure and winds
• When temperature is high air ascends leaving an area of low pressure
at the surface
• With low temp the air descend leaving a high pressure area at the
surface
• Air movement :high pressure area low pressure area this
movement defines wind

11. • pressure gradient : the amount of change in atmospheric pressure between high
and low pressure areas
PRESSURE GRADIENT FORCE (PGF): PGF causes the air to move from a high
pressure area towards a low pressure area along the pressure gradient
• PGF is stronger when pressure gradient is steeper resulting in
stronger wind

12. The Coriolis force
The force which deflects winds due to the earth’s rotation
It does not occur within 5 degrees of the equator
It is dependent on the strength of the wind, the force is stronger
when the wind is blowing faster
It deflects the winds from their north-south direction
Ferrel’s Law
States that as a result of the Coriolis force, the winds are deflected to their left in
the southern hemisphere and right in the northern hemisphere

13. activity
• Define Coriolis force
• Name 3 characteristics it has
• Define ferrels law