Transcript File - Thurso Geog Blog

ATMOSPHERE
Lesley Monk
Balfron High School
Session 2005/6
1
ATMOSPHERE
CELLS AND HEAT TRANSFER
A single cell model like in diagram 9 is too simplisticwe can find three interlinked cells!
THE THREE CELL MODEL;-FORMATION OF THE HADLEY CELL (1)
Insolation in tropical
areas causes warm air
to rise and spread
polewards, carrying
heat energy.
INSOLATION
SOLAR
ENERY
Nb; lots of new
terms to learn!
2
ATMOSPHERE
FORMATION OF THE HADLEY CELL (2)
Air cools and begins
to fall at about
30ºN and 30ºS of
Equator.
Cooled air returns
to the Equator.
NORTHERN HADLEY CELL.
SOLAR ENERGY
Heat energy is therefore
transferred from the
Equator to sub-tropical
latitudes.
SOUTHERN HADLEY CELL.
3
ATMOSPHERE
FORMATION OF THE POLAR CELL (1)
Intensely cold,
dense air sinks at
the poles, then
blows as surface
winds towards the
Equator.
4
ATMOSPHERE
FORMATION OF THE POLAR CELL (2)
At about 60ºN and 60 ºS,
the cold polar air is
warmed in contact with the
earth’s surface.
NORTHERN POLAR CELLS.
This warmed air rises and
returns polewards,
carrying heat energy.
SOUTHERN POLAR CELLS.
This circular motion is
called the POLAR CELL.
5
ATMOSPHERE
FORMATION OF THE FERREL CELL
Unlike the Hadley and
Polar Cells, the Ferrel
Cell is not driven by
differences in heat
energy.
The Ferrel Cell is
caused by friction
where air is in contact
with the other two
cells.
(The Hadley Cell drags
air down at about 30ºN
and S.
The Polar Cell causes an
uplift at about 60ºN and
S. )
6
ATMOSPHERE
THE THREE
CELLS
TOGETHER
Polar Cell
Ferrel Cell
Hadley Cell
Hadley Cell
Ferrel Cell
Polar Cell
7
ATMOSPHERE
It is well worth making sure that you
can see the rising and falling pattern
of these cells.
The next section uses this to work
out wind directions on the surface of
the earth.
There are handouts of the next few
slides; use them and diagram 13 to
answer the later questions on the
screen.
8
ATMOSPHERE
ASSOCIATED PRESSURE BELTS
HANDOUT
Rising air at the equator
causes the equatorial belt of
low pressure
Descending air at about
30ºN and 30ºS causes the
sub-tropical belt of high
pressure
Polar high pressure
Mid latitude low pressure
Sub-tropical high pressure
Equatorial low pressure
Rising air at about 60ºN
and 60ºS causes a midlatitude belt of low
pressure
Descending air at the
poles causes the polar high
pressure areas
Sub-tropical high pressure
Mid latitude low pressure
Polar high pressure
9
ATMOSPHERE
ASSOCIATED SURFACE WIND PATTERNS
Winds always blow from
high pressure to low
pressure.
They are deflected
because of the Coriolis
Force which come about
because of the rotation of
the earth. ( see later slide)
HANDOUT
COPY
TEXT
Winds in Northern
Hemisphere are deflected to
the right.
Winds in the southern
hemisphere are deflected to
the left.
These wind belts shift
seasonally. (See next section)
Polar high pressure
Mid latitude low pressure
Sub-tropical high pressure
Equatorial low pressure
Sub-tropical high pressure
Mid latitude low pressure
Polar high pressure
10
ATMOSPHERE
Answer these five questions fully in sentences.
Q1. What kind of pressure has rising air?
A.Low pressure has rising air.
Q2. What kind of pressure has falling air?
A.High pressure has falling air.
Q3. Name two latitudes with rising air.
A.The Equator and 60 degrees N/S have rising air.
Q4. Name two latitudes with falling air.
A.30 degrees N/S and the Poles have falling air.
11
ATMOSPHERE
Q5. Explain the two factors that make the NE
trade winds blow in the direction they do.
( You will need to be able to do this for any of the
winds in diagram 13 !)
i) Air is flowing from a high pressure area at 30
degrees north towards a low pressure area at
the Equator.
ii). The winds are being deflected by the
Coriolis force/ effect to the right as the area
is in the northern hemisphere.
12
ATMOSPHERE
Rossby waves and the Jet Stream
Not far above our
heads in the
northern UK is
where the Ferrel
and Polar cells meet.
This turbulence is
mainly responsible for
the series of
depressions and
anticyclones that
happen over Britain.
Here is where
powerful waves of
turbulence occur
called Rossby waves.
Read about these on
pages 10 and 11,
then answer the
questions on the
next slide.
13
ATMOSPHERE
Q1. In what direction do Rossby waves flow in the
northern hemisphere?
A.They flow towards the east in the northern
hemisphere.
Q2. What is the name of the contact zone
between the two cells?
A. It is called the Polar Front.
Q3. In what way is stage 4 like the formation of a
river’s ox-bow lake ?
A. Loops of turbulence get cut- off and isolated
from the main flow.
14
ATMOSPHERE
Q4.In what way is the Ferrel cell thought to be less
effective in atmospheric heat transfer?
A. It seems that winds and ocean currents transfer
more heat than this weak atmospheric cell.
THE CORIOLIS FORCE.
What happens when you set off in a plane to fly to
somewhere?
The earth turns beneath you, and you have to keep
adjusting your direction ! Watch……….
15
ATMOSPHERE
Destination
Direction of Earth-spin
has moved
Got the idea?
Note the
runners path is
curved!
Destination
has moved
Thirty
minutes in
Twenty
minutes in
Destination
has moved
Ten
minutes in
Initial direction
start
destination
16
ATMOSPHERE
Pages 14 and 15 are very technical !
The information is of the kind that can
give extra marks in an extended answer.
Ignore it at your peril !
We suggest that you read it at home
where you can think deeply about it !
You will need to have a basic
understanding of why the wind belts
are in different places at different
times of the year.
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