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
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
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