Transcript Lesson 3 Global Circulation

Lesson 3
General Circulation
Quick Recap
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Last lesson we learnt that uneven heating
across the earth led to movement of air.
Uneven heating is caused by a number of
factors eg seasons, surface coverage etc.
Movement of air occurs both horizontally
and vertically.
Air moves in mysterious ways!
Golden rules:
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Air ALWAYS moves from an area
of HIGH pressure to an area of
LOW pressure. (Filling up a void of
lower air pressure)
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The greater the differences in pressure,
the faster the wind will blow.
Cold air holds less moisture.
Basic Circulation
Hot tropical air
moves towards
the cold poles.
Cold polar air
moves towards
the warm
equator.
Remember the differences in the heat supply.
Remember air moves both horizontally and
vertically within the confines of the
atmosphere.
Movements…
at the equator
Once air starts moving
from hot and cold
places, a more
complicated circulation
pattern is revealed.
The effects of pressure
play an important part
in pushing or pulling
air, not to mention the
spin of the earth.
At the equator due to intense heating, the air lifts up freely (convection).
This results in buoyant air spreading out so there is less air at the surface
– ie LOW PRESSURE.
This movement vertically encourages cloud growth – rain – hence tropical
rainforests are found under areas of low pressure.
Movements…
at the poles
At the polar regions the
air is very stable – dry
and cold. This
encourages the air to
sink, creating HIGHER
pressure at the surface.
High pressure at the surface is found at regular locations across the globe.
Under these conditions, different biomes are found – typically deserts. EG
The North & South pole are both under high pressure – Cold deserts
The Sahara and Kalahari deserts are both under high pressure – Hot deserts
(Desert = Less than 250mm rain per annum)
http://www.youtube.com/watch?v=qh011eAYjAA
Coriolis
http://www-tc.pbs.org/wgbh/nova/elnino/anatomy/images/coriolis.gif
The Coriolis force deflects air to the right
in the Northern hemisphere (and to the
left in the Southern hemisphere) when
viewed along the line of motion. This is
due to the spin of the Earth, it is this
force that provides the surface winds
with their directions, otherwise they
would flow simply direct North South.
Coriolis videos
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http://www.youtube.com/watch?v=aeY9t
Y9vKgs&NR=1&feature=endscreen
http://www.youtube.com/watch?v=Kk7sX
kzmtp0&feature=related
Its all mixed up!
So far then, we know
that air moves from
high to low pressure
areas (Fig A).
A
Polar Cell
Ferrell Cell
Hadley Cell
Source areas of high and low
pressure follow a known
pattern.
B
•Air doesn’t simply move from the equator to the poles and vice versa (Fig A).
•The spin of the Earth (Coriolis Force) affects direction of winds.
•There are three large cells that act to transfer heat in the Northern &
Southern Hemispheres – Polar, Ferrell and Hadley (Fig B.)
Tri Cell
This model shows what we expect to
happen when air moves. It flows from
High to Low in each cell, transferring
heat energy as it moves.
Its all twisted! ~ Planetary Surface Winds
Collaborative Summary
Using these words / terms, complete a summary of
your understanding from today’s lesson.
Share with your neighbour and add something
extra to your partner’s work to develop it.
Coriolis
Surface
winds
High pressure
Low pressure
Converging
Diverging
Homework
1 Study the next slide which shows the average annual
global distribution of insolation at the Earth’s surface.
Describe and comment on the distribution shown. (7
marks)
2 With the aid of a diagram, describe the structure of the
atmosphere. (8 marks)
Global Insolation