Download Interactive 3-cell model answers

• Tropical areas
receive more
insolation (energy
from the sun) than
the polar regions.
• There is an energy
surplus at the
Tropics and an
energy deficit at the
Poles
• In theory this would result in the
Tropical regions getting warmer and the
Polar regions getting colder…
• In reality, energy is transferred
polewards…
• One of the ways in which this happens is
by atmospheric circulation.
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 rise ,creating a belt of
LP
• The warm air moves towards the
poles where it sinks,creating a belt
of HP
• Surface winds always blow from high
to low pressure
• This completes the Hadley Cell.
• In this way, surplus energy from the
Equator is transferred polewards.
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, Ferrel cell and polar
cell
The Hadley Cell
• The Hadley cell extends from the
equator to tropics
• Air at the equator is heated up.
• Warm air rises creating a zone of
LP
• Warm air moves polewards but
begins to sink
• The cold air sinks at 30 degrees
creating a zone of HP
• The cold air then flows back
towards the equator because
surface winds always blow from HP
to LP
The Polar Cell
• At the Poles, air is being cooled. Cold
air is dense and therefore sinks
• The descending cold air moves towards
the lower, warmer latitudes.
• As it moves towards the lower latitudes
it becomes warmer and therefore rises
at 60 degrees creating a zone of LP
• The rising warm air then moves
polewards completing the Polar cell.
The Ferrel Cell
• The Ferrel cell lies in between the
other two cells.
• The Hadley cells and Polar cells are said
to thermally indirect cells because they
are driven by different heating The
Ferrel cell is a thermally cell because it
is driven by friction between the other
two cells
The Ferrel Cell
• As the air in the Hadley Cell
descends at about 30ºN and
30ºS, it pulls the air beside it as
well, due to friction
• As air in the Polar Cell rises at
about 60ºN and 60ºS, it pulls
the air beside it up as well.
• In this way warm air is
transferred from the Hadley
cell to the Polar cell via the
Ferrel cell for cooling.
• And cold air is transferred from
the Polar cell to the Hadley cell
via the Ferrel cell for warming.
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.
Polar High Pressure
Polar Easterlies
Sub-Polar low pressure
Mid Latitude…
Sub-Tropical high
pressure
Equatorial low
pressure…
North East…