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AS Course
Module 3:
THE ATMOSPHERE
• The atmosphere is heated from BELOW
1. Solar energy hits the earth’s surface (short-wave)
2. The earth’s surface ABSORBS the short wave energy
from sun via CONDUCTION
3. Also the air directly above the earth’s surface is also
heated by CONDUCTION
4. The air above (30m and higher) is heated by
CONVECTION (eg hot air balloon) – this forms
cumulonimbus clouds.
5. As well as all this the short-wave radiation is reflected as
long wave (terrestrial radiation). This is emitted from the
earth’s surface and is absorbed by greenhouse gases –
such as Carbon Dioxide (CO2), Methane (CH4), CO
(Carbon Monoxide), Sulphur Dioxide (SO2). This process
is called GLOBAL WARMING.
The
Structure of
the
Atmosphere
Earth's Atmosphere
The Earth is surrounded by a blanket of
air, which we call the atmosphere. It
reaches over 560 kilometers (348 miles)
from the surface of the Earth, so we are
only able to see what occurs fairly close to
the ground. Early attempts at studying the
nature of the atmosphere used clues from
the weather, the beautiful multi-colored
sunsets and sunrises, and the twinkling of
stars. With the use of sensitive instruments
from space, we are able to get a better
view of the functioning of our atmosphere.
Life on Earth is supported by the
atmosphere, solar energy, and our planet's
magnetic fields. The atmosphere absorbs
the energy from the Sun, recycles water
and other chemicals, and works with the
electrical and magnetic forces to provide a
moderate climate. The atmosphere also
protects us from high-energy radiation and
the frigid vacuum of space.
The envelope of gas surrounding the Earth
changes from the ground up. Four distinct
layers have been identified using thermal
characteristics
(temperature
changes),
chemical composition, movement, and
density.
Troposphere
The troposphere starts at the Earth's
surface and extends 8 to 14.5 kilometers
high (5 to 9 miles). This part of the
atmosphere is the most dense. As you
climb higher in this layer, the
temperature drops from about 17 to -52
degrees Celsius. Almost all weather is in
this region. The tropopause separates
the troposphere from the next layer. The
tropopause and the troposphere are
known as the lower atmosphere.
Stratosphere
The stratosphere starts just above the
troposphere and extends to 50 kilometers (31
miles) high. Compared to the troposphere, this
part of the atmosphere is dry and less dense.
The temperature in this region increases
gradually to -3 degrees Celsius, due to the
absorbtion of ultraviolet radiation. The ozone
layer, which absorbs and scatters the solar
ultraviolet radiation, is in this layer. Ninety-nine
percent of "air" is located in the troposphere
and stratosphere. The stratopause separates
the stratosphere from the next layer.
Mesosphere
The mesosphere starts just above the stratosphere
and extends to 85 kilometers (53 miles) high. In
this region, the temperatures again fall as low as 93 degrees Celsius as you increase in altitude. The
chemicals are in an excited state, as they absorb
energy from the Sun. The mesopause separates
the stratosphere from the next layer.
The regions of the stratosphere and the
mesosphere, along with the stratopause and
mesopause, are called the middle atmosphere by
scientists. This area has been closely studied on
the ATLAS Spacelab mission series.
Thermosphere
The thermosphere starts just above the
mesosphere and extends to 600 kilometers (372
miles) high. The temperatures go up as you
increase in altitude due to the Sun's energy.
Temperatures in this region can go as high as
1,727 degrees Celsius. Chemical reactions occur
much faster here than on the surface of the Earth.
This layer is known as the upper atmosphere.
The upper and lower layers of the thermosphere
will be studied more closely during the Tethered
Satellite Mission (TSS-1R).
Questions 1>4:
1. Why does it get colder the further you go up a mountain?
• You are further away from the influence of conduction and
convection at the earth’s surface – as the atmosphere is
heated from BELOW
• “Albedo effect” = ISR (incoming solar radiation) is reflected
off lighter surfaces – eg snow
• Greater windspeeds higher up because there is less friction
with earths surface so any heat there is taken away
• There is less pressure the higher up you go – which means
that there are less molecules of air to absorb the ISR /
reflected LW radiation (from earth)
2. Where would you find a higher % of water vapour?
• Above trees – transpiration taking place
• Over oceans – where evaporation is taking place
• Clouds – where water vapour has condensed
3. In what ways are humans contributing to the greenhouse
effect?
•
CO2 from power stations; from deforestation in Amazon;
•
CO from car combustion
•
CH4 from animals / rice fields
•
So2 from power stations
4. Why is the atmosphere thicker at the equator than at the
poles?
•
The spinning effect of the earth “pulls” air into the equator
away from the poles
The Ozone Hole
Ozone Hole Splits, Spring 2002
(total area smaller than 2001)
September 25, 2003
• Solar constant
• Distance from the sun
• Angle of the sun in the sky
• Seasonal variations
The amount
of
energy
which
is
received
from the sun
varies with
sunspot
activity.
Its
exact
value is not
known but is
about 1380W
m2
The earth’s distance from the sun varies
throughout time and this can cause a 6% variation
in the solar constant. It has been argued that this
has been enough to cause the ice ages.
The curvature of the earth means that there is TWICE as much
incoming solar radiation reaching the earth's surface at the
equator (during the autumn and spring equinox’s) than there is at
600N or S
It is clear in this diagram
how much more land
area the same “bundle”
of solar radiation has to
cover than that at the
equator
EARTH
Equator
During
theNorthern
summerHemisphere
months when
thethe
Northern
is tilted
During the
winter,
angle at Hemisphere
which the incoming
The
are
short
during
winter
there
is little
time
for
the
The days
towards
time
the
of year
sun,
makes
the
angle
an
enormous
at
which
the
difference
incoming
to
solar
the
amount
radiation
of
solar
radiation
reaches
thethe
surface
isand
very
low
and
each
bundle
of incoming
radiation
The
N
Hemisphere
summer
days
are
long
which
means
there
is
solar
radiation
to aheat
the ground
after
the
long
nights.
Noteover
that
the North
is
having
to
heat
far
larger
area
of
land.
The
is directly
overhead
the
radiation
strikes
the
which
earth’s
reaches
surface
the
isearth’s
high.
The
surface
sunsun
is directly
the
Tropic
more
time
for
the
ground
to
be
heated
by
incoming
solar
radiation
0 SOUTH
Pole
receives
no insolation
at23.5
all during
this
time
Tropic
of Capricorn,
ofequator.
the equator.
of Cancer,
which
iswhich
23.50is
NORTH
of the
Consequently the
summers
in the
N Hemisphere
areare
hot.
Consequently
N Hemisphere
winters
cold.
600N. This is the
latitude of northern
Scotland
Equator
Earth’s
axis is on
a 23.50 tilt
SUN
December 21st
Midwinter's day in the
Northern Hemisphere
June 21st
Midsummer's day in the
Northern Hemisphere
September 21st
Autumn equinox
Twice during the
The sun is
year the sun is
“sideways on” to
directly overhead
the earth and as
at the equator
a result the tilt is
and the N and S
negated
Hemispheres
receive equal
amounts of I S R
March 21st
Spring equinox
SUN
Consequently there is
12 hour night and 12
hour day across the
entire globe, give or
take 15 minutes
Earth’s
axis is on
a 23.50 tilt
For an excellent graphical explanation of the
seasons go to;
www.usatoday.com/weather
As a result
of
ISRblanket
never
Consequently
Stratus
cloudsdesert
on clouds,
theenvironments
other 23%
hand of
(Grey
have
the
greatest
cloud) are
Cumulus
clouds
(the
“fluffy”
ones)
reflect
a
lot
of
ISR
dueitto
Based
on
this
information
can
you
explain
why
The
During
However
As
apicture
result
the
atthe
summer
is
it
NIGHT
is
complicated
warmer
all
months
the
at
heat
night
further
it is
on
when
warmer
the
asequatorial
itground
there
depends
during
isescapes
heavy
the
what
day
reaches
earth's
surface.
dark.
diurnal
(day
and
night)
variation
and
rainforests
their
light
clearly
colour.
reduce
the
amount
ISRitduring
the
SORT
ifClouds
into
cloud
there
space
OF
cover.
is
CLOUDS
no
as
there
are
are
as in
all
no
the
the
clouds
sky
ISRthe
can
toof
hold
reach
in…...
the
earths
is
warmer
incloud,
the
day
during
winter
when
have
the
least
These
day, prevent
butreflected
this longwave
doesn’t
necessarily
radiation
leaving
mean itthe
will
lower
bethe
colder!
20%
and
3%
is absorbed
by
surface……….
This
isis
due
to the ALBEDO
effect,
which we will
look at later.
there
is
cloud?
atmosphere
and can
keep the environment WARMER
water droplets
themselves
6% reflected /
absorbed by
atmosphere
Earth’s
albedo
30%
20% reflected
by clouds
4% reflected from
earth’s surface
16% absorbed by dust
and gases
3% absorbed
by clouds
•The
6% is
either
absorbed
•Much
It
is remaining
themore
absorption
(over
20%)
and
scattering
incoming
of by
stratospheric
ozoneby(O)
or
reflected
byand
the
• different
16%is absorbed
atmospheric
gases
radiation
wavelengths
is “scattered”
of
by
ISR
the
bygases
gases
and
atmosphere.
The
by
and
dust.
is proportion
radiated
longwave
dust.
dust
which
ThisThis
incoming
cause
theradiation
sky as
toabsorbed
be
isblue
thenduring
ozone
is as
UV
radiation,
which
isthe
extremely
radiation
which
in turn
warms
known
the
day.
“diffuse
radiation”.
harmful
to human skin and eyes (known to be
atmosphere.
carcinogenic) as well as harmful to plants
Aurora borealis / australis

The northern / southern lights

Thermosphere and uppermost Mesosphere
– solar wind (clouds of electrically charged particles)
– Earth’s magnetic field directs them towards poles
– excite oxygen (O) and nitrogen (N2) ions in ionosphere
 emit light
4% is reflected from the earth’s surface without being
absorbed. This is due to the ALBEDO effect which was
mentioned earlier…….
Different surfaces absorb and reflect varying amounts of
ISR. This is known as their albedo.
Place the following surfaces in order, based on the amount of
ISR they reflect. Have a guess at the amount of ISR they
reflect
•Oceans
•Light coloured
and darkdeserts
soils
<10%
•Coniferous
•Coniferousforest
forest
15%
•Grassland
•Fresh snow
and deciduous forest
25%
• •Oceans
Light coloured
and dark
deserts
soils
40%
•Fresh
•Grassland
snow and deciduous forest
85%
and landterms
are twothen,
clear examples
these
InWater
layman's
it takesoftwice
Being
a body of
therefore
has a by
Thenear
situation
is water
further
complicated
variations.
asthe
much
energy
to
heat
water,
BUT
noticeable
effect
on
the
climate
of
a
landmass
as the
different
ways
in
which
the
earth’s
It requires
4.2kj
of energy to heat 1kg of water by
following
slides
demonstrate.
ALSO
it
needs
to LOSE
twice
as
much
0
surfaces
heat
and
cool.
This
is
obviously
1 C.
toacool
downwhen
by the
sameatamount.
key factor
looking
climate as it
In comparison it takes only 2.1kj to heat 1kg of
is essentially the ground which heats the
soil.
As a result the oceans are cooler in the
atmosphere.
Sand requires
0.84kj. in the winter and
summer
but only
warmer
The
way inas
which
materials
absorb and
are
known
THERMAL
RESERVOIRS
release heat energy is known as their
SPECIFIC HEAT CAPACITY. It is the
amount of energy required to raise 1kg of
a substance by 1C.
Inland areas are far
from the sea and
Note
thefrom
warm
away
the and the cold areas.
warming influence
Anyofideas
as to why this is?
the Caribbean
Keeps
inland
areas
warm in
winter
Warm
Caribbean
400 North
400 North
Note how much farther
north the UK is compared
to the latitude line.
Any ideas as to why it
isn’t extremely cold?
(We are the same latitude
in Bedford as Calgary in
Canada)
400 North
400North
GCM
The
World
January
29th 2002
The
World
January
29th 2002
Equatorial Low Pressure Trough:
Clouds and Rain


The Intertropical Convergence Zone (ITCZ)
Doldrums
L
ITCZ
Subtropical High-Pressure Cells:
Hot Desert Air


The Horse Latitudes
Broad Cells of High
Pressure
H
AIR MASSES
Unstable Air
Instability is caused by an air mass rising off the ground. This
can be caused for example, by a body of cold air (in this case polar Maritime
air) getting warmer as it moves further south – ie
Towards the equator. As the air rises it COOLS. As it cools down it’s capacity
to hold moisture decreases. Another way of saying this is that it increases in
humidity. When the humidity reaches 100% - the air is said to be saturated –
or reaches its “DEW POINT TEMPERATURE”. At this point air held as water
vapour condenses and water droplets or CLOUDS FORM. At the same time
LATENT HEAT OF CONDENSATION is released which gives the rising air
more upward momentum (like a hot air balloon). This forms cumulonimbus
rain clouds.
Polar Maritime Air Mass
North
Pole
UK
Cold air begins to warm as
It travels further south therefore
Rises off the ground – leading
To UNSTABLE AIR
Equator
DEPRESSIONS
Atmospheric Pressure
Pressure can be
thought of as the
weight of all
overlying air
(though, in reality,
pressure exerts
force in all
directions).
Average Sea Level
Atmospheric Pressure:
29.92” of Mercury
76 cm of Mercury
1013 millibars (mb)
Mercury Barometer
- Invented by Toricelli, 1643
Warm Front
Cold Front
Cold Air
Warm air
Cold Polar
Maritime Air
Warm Tropical
Maritime air
WEATHER ASSOCIATED WITH THE PASSAGE OF A CLASSIC DEPRESSION
Ahead of the warm
front
Passage of the
warm front
Warm sector
Passage of the cold
front
Cold sector
Pressure
starts to fall steadily
continues to fall
steadies
starts to rise
continues to rise
Temperature
quite cold, starts to
rise
continues to rise
quite mild
sudden drop
remains cold
Cloud cover
cloud base drops and
thickens (cirrus
and altostratus)
cloud base is low and
thick
(nimbostratus)
cloud may thin and
break
clouds thicken
(sometimes with
large
cumulonimbus)
clouds thin with some
cumulus
Wind speed and
direction
speeds increase and
direction backs
veers and becomes
blustery with
strong gusts
remain steady, backs
slightly
speeds increase,
sometimes to
gale force, sharp
veer
winds are squally
Precipitation
none at first, rain
closer to front,
sometimes snow
on leading edge
continues, and
sometimes
heavy rainfall
rain turns to drizzle or
stops
heavy rain, sometimes
with hail,
thunder or sleet
showers
ANTICYCLONES
Air Pressure
Force exerted by air molecules per unit
area
(Result of compression of the air by
gravity).
This pressure force is omnidirectional.
LOCAL ENERGY
BUDGETS
Mountain-Valley
Breezes
Land and Sea Breezes
L
H
x
5x
Temperature
Inversions
An upside-down
situation
The ‘Normal’ Situation
105’ 38°F
105’ 38°F
64’ 40°F
64’ 40°F
32’ 40°F
32’ 40°F
16’ 41°F
8’ 41°F
16’ 41°F
8’ 41°F
Temperature Inversions


These are when the
‘normal’ situations
are reversed ie
when warmer air
overlies colder air.
This can be at low
level
Temperature Inversions


These are when the
‘normal’ situations
are reversed ie
when warmer air
overlies colder air.
This can be at low
level or at high level
Temperature
Inversions

There is a natural
inversion in our
atmosphere as the
stratosphere is the
layer that absorbs
most of the
ultraviolet radiation
(high level)
Temperature Inversions

High level inversions are also found in
depressions, when the warm sector overlies the
cold sector (occlusion)
Temperature Inversions


Low level or ground
inversions occur in
anticyclonic conditions
when there is a rapid
loss of energy at
night.
The air near the
surface is cooled by
conduction of heat to
the cold ground. The
lower layer is
therefore colder than
Temperature Inversions


Low level or ground
inversions occur in
anticyclonic conditions
when there is a rapid
loss of energy at
night.
The air near the
surface is cooled by
conduction of heat to
the cold ground. The
lower layer is
therefore colder than
Temperature Inversions

A classic inversion is where the hot emissions
given off by industrial chimneys trap in the
colder air below
Signs of a surface
inversion in the
early morning
Lack of heavy cloud cover
Windless or light
variable wind
Ground Fog
Frost (or dew)
HOT AIR – more able to carry
moisture
Cold Air descends and condenses forming fog
Smoke from a chimney forming a layer
Surface inversion - early morning