Transcript ATMOSPHERE

ATMOSPHERE
http://www.teachersdomain.org/resource/ess05.sci.ess.earths
ys.hologlobe/
EARTH AS A SYSTEM
STRUCTURE OF THE
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ATMOSPHERE
Thermosphere
Mesosphere
Stratosphere
Troposphere – contains 75% of the mass of the
atmosphere and almost all of the moisture and
dust.
http://www.teachersdomain.org/resource/ess05
.sci.ess.watcyc.vertical/
TROPOSPHERE
Temperature decreases by 6.4oC every 1000m
– lapse rate
 Solar radiation heats the air by conduction
 Contains most of atmospheric water, vapour,
cloud, dust
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STRATOSPHERE
Steady increase in temp. caused by increasing
concentration of ozone O3 which absorbs
ultraviolet radiation.
 Winds light and increase with height
 Pressure falls and air is dry
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MESOSPHERE
Temperature falls rapidly as no water vapour,
cloud dust or ozone to absorb incoming
radiation
 Lowest temperature –90o C and strongest
winds
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THERMOSPHERE
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Temperatures rise rapidly with height – 500o C
due to increasing proportion of atomic oxygen
which absorbs incoming UV radiation (like
ozone)
GLOBAL HEAT BUDGET
THE GLOBAL HEAT BUDGET
The atmosphere system involves inputs
and outputs.
 Incoming solar radiation is balanced by
outgoing terrestial energy from the earth.
 The balance between input and output is
usually referred to as the Global Heat
Budget.
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Input begins with solar energy
(insolation). Some insolation is:
 Reflected by clouds and
scattered by gas particles
 Absorbed
by water vapour, dust
and clouds.
Output is in the form of long wave
radiation emitted from the earth –
this balances the input of energy
from the sun:
 94% of this radiation is absorbed by
water vapour and CO2 in the
atmosphere.
 6% is radiated back into space.
LATITUDINAL VARIATIONS
 As
well as a vertical transfer of
energy between earth and space
there is also a horizontal transfer
of energy between high and low
latitudes.
 These
energy variations are more
extreme between the tropics and the
poles. Such marked contrasts are
referred to as the global
temperature gradient and are the
result of a number of factors:
 The
curvature of the earth
 Due to the curvature of the
earth, the equator is closer to the
sun than the poles and as a result,
insolation at the equator is more
concentrated.
Atmosphere penetration
 The sun’s energy also passes
through a greater depth of
atmosphere at the poles causing a
lot of energy to be diffused.
The Albedo effect
 Ice and snow reflect more solar
radiation back into space making
them cooler whereas areas of
dense vegetation absorb radiation
making them warmer.
SEASONAL VARIATIONS
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Seasonal variations in amount of radiation received by
the earth with latitude
Sun ‘appears’ to be at Tropic of Cancer mid-June, so
northern hemisphere receives more insolation
Mid-December the sun ‘appears’ to be at the Tropic of
Capricorn and so the southern hemisphere receives
the maximum insolation
ENERGY TRANSFER
 Such
an imbalance in energy receipt
could theoretically result in the lower
latitudes becoming warmer and the
higher latitudes becoming even
colder. In reality however, energy is
transferred from areas of surplus to
areas of deficit by atmospheric
circulation and by ocean currents.
ATMOSPHERIC CIRCULATION
 The
three cell model is a useful
tool in describing atmospheric
circulation and energy transfer.
 Circulation 1
 Circulation 2
THE HADLEY CELL
 This
extends from the equator to
about 30 N and S of the equator.
The intense heating at the
equator causes the air to expand
and become lighter, producing an
area of low pressure.
 This
warm, rising air contains large
amounts of moisture which condenses
to form cumulonimbus clouds and
heavy rainfall. The rising air then
spreads polewards and sinks to the
sub-tropics. The sinking air produces
high pressure resulting in clear skies
 And
little precipitation (these
areas correspond with the desert
areas of the world)
THE POLAR CELL
 Air
over cold surfaces will become
cold, contract and become heavy. It
will therefore sink and produce an
area of high pressure. The sinking air
moves towards lower latitudes where
it will expand and rise back up
creating a cell.
THE FERREL CELL
 The
Ferrel Cell lies between the
Hadley Cell and the Polar Cell.
The HC and the PC are thermally
direct cells (powered by
temperature differences).
 The
Ferrel Cell is a thermally indirect
cell because it is powered by the
other two. The FC transfers warm
air from the Hadley cell to the high
latitudes and transfers cold air form
the PC to the low latitudes for
warming.
ATMOSPHERIC CIRCULATION – THE
FULLER PICTURE
 Atmospheric
circulation is a lot
more complicated than is
suggested by the three cell
model. Recent research questions
the existence of the Ferrel Cell.
In place of the Ferrel Cell it is now
argued that there are:
 Alternating patterns of high and low
pressure which travel at relatively low
levels.
 A series of high level, horizontal
wavelike motions called Rossby
waves.
 Rossby
waves are very large, high
velocity belts of wind operating in the
upper atmosphere. They have a
distinct wave like motion as they
snake their way across the globe. At
their core are long, narrow cylinders
of very fast flowing air called jet
streams.
JET STREAMS
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Teachers' Domain: The Effect of Jet Streams on
Climate
GLOBAL WIND CIRCULATION
 Whatever
the actual workings of
energy transfer and atmospheric
circulation, broad global patterns
of winds and pressure can be
identified:
MODEL OF GLOBAL WIND
CIRCULATION
 The
model of Global Wind
Circulation is more complicated
than it would appear due to
several factors:
 The
earth’s tilt and consequential
seasonal contrasts.
 In
June in the Northern
Hemisphere, the earth’s axis is
tilted towards the sun and the
sun appears directly overhead in
the Tropic of Cancer.
 In
December, the earth’s axis
tilts away from the sun and the
sun appears to be overhead at the
Tropic of Capricorn.
 The
apparent movement of the
overhead sun is important
because it controls the belt of
maximum heating which moves
with the sun. This called the
thermal equator.
The distribution of land and sea.
 The wind pattern is more consistent in the
Southern Hemisphere especially above
latitude 30 degrees south as there are
virtually no land masses to interrupt the
winds and heating and cooling properties
of the oceans means that a relatively
consistent wind pattern results.
 Over
the Northern Hemisphere,
the large land masses result in an
altered wind pattern due to the
more extreme temperature
differences experienced over the
continents in summer and winter.
 Low
pressure is dominant in the
summer due to the intense
heating of continental interiors
(winds therefore spiral inwards
anticlockwise towards the centre
of the low pressure).
 High
pressure dominates in winter
and winds blow outwards in a
clockwise direction.
OCEAN CURRENTS
 Sea
water has a high thermal
capacity, so the oceans are an
effective store of thermal energy.
In contrast with the land, the seas
warm to a greater depth and also
move and so redistribute this energy.
Upper ocean currents are generated by
prevailing winds blowing across the
surface of the ocean. These are
influenced by the rotation of the earth
and the distribution of the land masses.
The currents largely flow in loops called
gyres.
 http://www.teachersdomain.org/resource/
ess05.sci.ess.watcyc.gulfstream/
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 In
addition to the surface ocean
currents of the world, there is
also and oceanic conveyor belt , or
deep ocean circulation, that
corresponds to the atmosphere’s
climate.
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Antarctica is important in this pattern of
movement, here vast amounts of water
freeze into ice, this loss of fresh water
causes the remaining sea water to become
more saline and therefore more dense.
This denser water consequently sinks and
makes its way northwards towards the
equator where it is warmed and returns
southwards.
 Cold
ocean currents flow from the
poles.
 Warm ocean currents flow from the
equatorial regions.
 http://www.teachersdomain.org/reso
urce/ess05.sci.ess.watcyc.convey2/
 Below
latitude 30 degrees, the
west coast of continents have
contact with cold ocean currents
e.g. Peru, and the east coast of
continents have contact with
warm ocean currents e.g. Brazil
current.
 Above
45 degrees, the position is
reversed – west coast in contact
with warm currents e.g. NAD, and
east coast in contact with cold
current e.g. Labrador current.
 In
the Pacific and Atlantic oceans
large loops (gyres) appear which
are associated with cells of subtropical high pressure.
RAINFALL AND VEGETATION IN AFRICA
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Rainfall
Vegetation
ITCZ
 Critical
to our understanding of
the varying rainfall totals and
their seasonal distribution in
tropical Africa is the seasonal
movement of the ITCZ.
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The ITCZ is a belt of low pressure
produced by the combination of
equatorial heating and the
convergence of trade winds, and
migrates in response to the changing
location of the thermal equator. (see
hand out)
THE INTER TROPICAL CONVERGENCE
ZONE
 As
the airflows converge at the
ITCZ, they rise and create a zone of
clouds and rainfall. Once the air
ascends it diverges and flows
polewards, descending over a wide
area centred around 30 degrees N
and S. As it descends it is warmed
and results in dry, cloudless
conditions.
 The
descending air at the subtropics
will be affected by the air mass at
the Earth’s surface. The most
important air masses which affect
Africa are Tropical Continental and
Tropical Maritime.
 The
Tropical Continental air mass
(Harmattan) is a hot and dry air
mass.
 The Tropical Maritime is a hot
and wet air mass.
The AFRICAN ITCZ REGION
 In
July, the ITCZ has reached its
most northerly extent and it pulls
in hot, moist tropical maritime air
bringing the Wet Season to West
Africa.
 By
January, in response to the
changing position of the thermal
equator, the ITCZ has migrated to
the Tropic of Capricorn. Most of
Africa north of the equator will
experience its dry season at this
time.
 West
Africa is also influenced by
Tropical continental air at this
time bringing dry, dusty
conditions.
ITCZ IN AFRICA

http://people.cas.sc.
edu/carbone/module
s/mods4car/africaitcz/index.html
The ITCZ in Africa.url
Continental
tropical air
Maritime tropical
air
ATMOSPHERE
IN JANUARY
N
S
Hot dry cT
air
Wet warm mT
air
Moves this way
‘Harmattan’ wind
HEAVY RAINS
Gulf of Guinea
Coastal areasequatorial climate
Inland areas- savanna
climate type
Copy diagram
Sahara- Desert
climate type
79
Continental tropical air
Maritime tropical
air
Continental tropical air
Maritime tropical
air
ATMOSPHERE
IN JULY
S
N
Compare the January and July diagrams.
Hot dry cT
air
Wet warm mT
air
Moves this way
HEAVY RAINS
Gulf of Guinea
Coastal areasequatorial climate
‘Harmattan’ wind
LIGHT RAINS
Inland areas- savanna
climate type
Copy diagram
Sahara- Desert
climate type
82
http://www.srh.weather.gov/srh/jetstream/tropics/itcz.
htm
Continental tropical air
Maritime tropical
air
CLIMATIC CHANGE
 Causes
of climatic change:
 Natural causes
 Man-made causes
NATURAL CAUSES
 Variations
in solar energy – sun
spot activity occurring in cycles.
 Milankovitch’s Cycle (wobble, roll
and stretch theory)
 Composition
of the Earth’s
atmosphere – volcanic activity can
add dust particles into
atmosphere increasing the
absorption and scattering of
incoming solar radiation.
MAN MADE CAUSES
 Increased
CO2 levels
 Deforestation – increases CO2 levels
 Flatulent cows - increased population
pressure has led to increased food
production – cows produce a lot of
methane gas.
 Deforestation,
soil erosion etc
have increased the albedo effect.
 Increased use of CFCs in aerosols
etc.
CONSEQUENCES
 Predicted
temp rise of 1.5 to 4.5
degrees C – this would threaten
wildlife, affect agricultural areas,
tropical diseases would spread
 Sea
levels would rise – many low
lying areas would be flooded.
 Increase in extreme weather
conditions.
SOLUTIONS
 Reduce
CO2 emissions
 Reduce use of nitrogen fertilisers
 Less intensive livestock
production
 Ban CFCs