Temperature radiation climatology

1. TEMPERATURE & RADIATION BUDGET
Temperature and Altitude
�The graph shows the Environmental Lapse
Rate - the average global temperature of air
at altitude. It does not represent rising or
descending air.
�This graph would be different for any place
and at any time (it varies daily, seasonally).
�Temperature tends to decrease with altitude
�Air temperature changes fastest nearer the
earth’s surface (air warms and cools mainly
by contact with the earth)
�The troposphere contains most water
vapour and has the most variable
temperature, especially at low levels.
�Temperature inversions (when it increases
with altitude) occur where various gases
cause varying rates absorption of radiation
�The tropopause is the lowest permanent
inversion; its height varies from 8km at the
poles to 16km at the equator
�Temperature inversions often occur at
ground level when rapid ground cooling
causes air at ground level to be colder than
air 1-200m above the surface.
Greenhouse gases
ENVIRONMENTAL LAPSE
RATE

2. SOLAR ENERGY - VARIATIONS
� Solar energy is
transmitted to earth in the
form of short and long
wave (SW or UV, and LW)
radiation, since the sun is
very hot. It is SW, UV
radiation that is absorbed
effectively by ozone. This is
insolation.
� Radiation may be
absorbed only by mass; the
more mass, the more
absorption.
� The earth also emits
radiation (all bodies at a
temperature above -273°C
do); this radiation is almost
entirely long wave (LW)
since it is cooler than the
sun. This LW radiation is
more effectively absorbed
by greenhouse gases (CO2,
Methane etc).
� The amount of
insolation emitted by
the sun varies with sun
spot activity. This
causes fluctuations of
up to 2% on a time
scale of decades, or
more.
� The amount of
insolation reaching the
earth’s outer
atmosphere varies with
distance and variations
of the earth’s orbit.
This causes fluctuations
of up to 4% on a time
scale of centuries or
more.
INSOLATION is the energy
which drives the atmospheric
weather system. All winds,
humidity and weather systems
are driven by variations in
temperature.
Climate (long term variations in
the state of the atmosphere) is
related to global and continental
location.
Weather (short term variation)
is related to small scale changes
in time and space.

3. Low sun (as sunset) shows more red
due to atmospheric dust and pollution
GLOBAL VARIATIONS in INSOLATION
Insolation received at the earth’s
surface varies with latitude. The
higher angle of the sun in the sky at
the equator conveys more energy per
unit area than at higher latitudes.
� A given amount of radiation covers
a smaller area when overhead than
when at a low angle; it is more
concentrated
� Radiation passes
through a greater
length of
atmosphere when
at a low angle in
the sky than when
overhead.
Atmospheric gases,
dust and vapour
absorb more
energy before it
reaches the earth’s
surface.
A high sun is more
effective than a sun
low in the sky

4. DAY LENGTH
Antarctic circle
66.5° S
Arctic circle 66.5° N
North Pole 90° N
South Pole
90° N
Equator
0°
Tropic of Cancer
23.5° N
Tropic of
Capricorn 23.5° N
Six months daytime (March-Sept), six
months night (Sept - March)
Six months daytime (Sept - March), six
months night (March-Sept)
One day with 24 hours daylight
(June 21st); one day with 24 hours
darkness (Dec 21st)
One day with 24 hours daylight
(March 21st); one day with 24
hours darkness (June 21st)
Sun is overhead once a year (June
21st). Day length always at least
10 hours.
Sun is overhead once a year
(Dec 21st). Day length always at
least 10 hours.
Constant day length - 12 hours day
and night all year round
Lengths of day and night
vay more between the
seasons at higher
latitudes. This makes
climate more seasonal at
the poles than the equator
More
seasonal
More
seasonal

5. CONTINENTAL SCALE VARIATIONS
Satellite photo
taken in daytime
in June over
Scandinavia.
Warmer surfaces
show darker. Note
that land is darker
than sea (ie land is
warmer).
Satellite photo
taken at night
over Britain in
January. Warm
surfaces show
darker. Note
that sea is
darker than the
land (ie sea is
warmer).
REASONS FOR CONTINENTAL
TEMPERATURE CONTRASTS
� Water has a higher specific heat than land
ie: it takes more energy to heat up an equal
mass of water by 1°C than it does land. Water
stores heat energy more effectively than land.
� Insolation is concentrated into the top few
cm of the land, but is dispersed over the
surface 10-20m of water.
� Water loses energy through evaporation
and loss of latent heat.
� Turbulence causes warmer water to be
mixed with colder water, so temperatures
remain more constant.
� Reflectivity is NOT a cause.
EFFECTS
� Temperatures of the sea vary less than on land
� Land near the sea has temperatures moderated
� The larger the ocean, the greater the effect
� Land temperatures vary more; the larger the land
mass, the larger the variation of temperature.
� Continental scale land masses have a more
seasonal climate.
� Contrasts between day and night are felt over a
small scale (a few km)

6. SMALL SCALE TEMPERATURE VARIATIONS
ALBEDO is the reflectivity of the earth’s surface. Darker colours
have a lower albedo; it absorbs more incident radiation than lighter
colours. On the photo, the snowcapped mountains have the highest
albedo, the forest the lowest. Ice cover at the poles has a high
albedo, further reducing temperature. Water has a surprisingly low
albedo, unless it is calm and the sun is at a low angle. Albedo of
vegetation varies seasonally; albedo of earth varies with water
content. Cloud cover also increases albedo, and changes over time.
ASPECT is the angle from which the
sun shines. In Europe, south facing
slopes are warmer than north facing.
In the southern hemisphere, the
aspects are reversed. On the photo
above, some snow remains on the
north facing slope; none on the south
facing slope. A south facing aspect (in
Europe) gives a higher angle of the
ALTITUDE causes temperature
to decrease (by about 0.6°C per
100m). Air is warmed mainly by
contact with the ground, so air at
altitude is colder. It is also at
lower pressure ( less dense) so
absorbs insolation less effectively.
Hence snowcapped peaks.
These small scale factors
vary over time.
Vegetation changes daily
and seasonally, with
growth and human
harvest.
Moisture content may
change the albedo.
Wind and sun angle alter
the albedo of water.
Cloud cover also affects
reflectivity; wind and
rain affect evaporation
rates, vegetation and
moisture content
North
facing
South
facing

7. ENERGY CASCADE - DAY
DAYTIME insolation takes a variety of pathways. Incoming SW radiation is absorbed by
mass, hence more effectively by the earth’s surface than by the atmosphere whose gases are much
less dense.
The diagram represents a global average; the figures clearly vary with the angle of the sun, day
length, cloud cover, humidity, albedo, aspect and altitude. They vary from place to place and over
time (seasonally, diurnally and shorter time scales).

8. ENERGY CASCADE -NIGHT
NIGHT-TIME energy flows vary from those at daytime. Outgoing terrestrial radiation is LW
(the earth is colder than the sun) and continues over 24 hours. In the day, it is usually less than the
incoming solar radiation, so the earth warms up and soil heat flow is downward. At night, it is clearly
greater than insolation and soil heat flow is upward. Heat is also transferred by evaporation and
condensation, and by movement of warm or cold air or water (sensible heat flow) in the form of winds
and ocean currents. Again, this represents a global average which varies in time and space.

9. GLOBAL HEAT FLUX
� At 40°N and S, there is a balance of insolation with
outgoing LW radiation over the year.
� Insolation exceeds LW radiation in the daytime, and in
summer; the reverse is true at night and in winter.
� Polewards of 40°N and S, there is an annual heat
deficit, despite periods of surplus during some days and
in summer.
� Equatorwards of 40°N and S, there is an annual heat
surplus despite periods of deficit at night and in winter.
� Without movement of heat energy, the poles would
become steadily colder and colder, while the equator
would get progressively warmer. This clearly does not
happen.
� This heat transfer (flux) occurs by:
� Ocean currents; cold polar water flows towards the
equator while warm water flows from equator to pole.
� Winds which blow warm air to towards the poles and
cold to the equator.
� An excess of evaporation which takes up and stores
latent heat in water vapour, releasing it towards the pole
where it condenses.

10. OCEAN CURRENTS
Cold Sea temperature
Warm
Labrador current carries
cold water from equator
to pole down east coast of
N.America
Gulf Stream
carries warm
water from
equator towards
the pole, and NW
Europe
A similar anti-clockwise movement of warm
water polewards, and cold water
equatorwards can be seen in the Pacific.
Cold and warm winds blow in similar fashion,
though are not constrained to the oceans!

11. HEAT TRANSFER by HUMIDITY
POLES - Precipitation exceeds evaporation
at high latitudes; condensation releases latent
heat stored in water vapour.
EQUATOR -
Evaporation exceeds
condensation (and
precipitation); this uses
heat energy and stores it
in the form of water
vapour. Red shows high
humidity from high rates
of evaporation
LATENT HEAT is also
transferred from sea to
land in this way.
Evaporation exceeds
condensation over
oceans (which uses
heat); condensation is
greater over land,
which is heated up -
especially in winter.

12. The GREENHOUSE EFFECT, like a real greenhouse (below)
is to allow heat in, but not out. Gases in the atmosphere (CO2,
Methane) naturally trap outgoing LW radiation more
effectively than they do incoming SW radiation. This retains
heat, warming the earth’s atmosphere.
GREENHOUSE EFFECT & OZONE
DEPLETION
Ozone traps UV (SW)
radiation from
reaching the earth’s
surface. Human
pollutants (CFCs etc)
are destroying this
protective layer and
causing cancers of the
skin in Australia -
near the Antarctic
hole in the Ozone
layer.
THE ANTARCTIC
HOLE IN THE
OZONE LAYER
This has, over geological
time, been in balance.
Now, human activity is
increasing such gases so
the warming effect is
(possibly) beyond recall.
This is the modern
Greenhouse Effect