1. Lesson 1Lesson 1
Structure of theStructure of the
AtmosphereAtmosphere
Specification: Major climate controls

2. DefinitionsDefinitions
 Weather – day to day changes inWeather – day to day changes in
the state of the atmosphere.the state of the atmosphere.
 Climate – average weatherClimate – average weather
conditions over a longer period ofconditions over a longer period of
time – 30 years.time – 30 years.

3. What is the Atmosphere?What is the Atmosphere?
An atmosphere is defined as the gaseousAn atmosphere is defined as the gaseous
envelope that surrounds a celestial body.envelope that surrounds a celestial body.
Therefore, the Earth, like other planets inTherefore, the Earth, like other planets in
the solar system, has an atmosphere, whichthe solar system, has an atmosphere, which
is retained by gravitational attraction andis retained by gravitational attraction and
largely rotates with it.largely rotates with it.

4. Who studies the Atmosphere?Who studies the Atmosphere?
Learning about different states of theLearning about different states of the
atmosphere enables science to understandatmosphere enables science to understand
and predict changes on a range of scales.and predict changes on a range of scales.
Meteorology is the subject that studiesMeteorology is the subject that studies
the chemical and physical properties ofthe chemical and physical properties of
the atmosphere together with its fields ofthe atmosphere together with its fields of
motion, mass and moisturemotion, mass and moisture..

5. How was is formed?How was is formed?
At the time of the Earth's formation around 4.5 billion years ago there wasAt the time of the Earth's formation around 4.5 billion years ago there was
probably no atmosphere. It is believed to have come into existence as aprobably no atmosphere. It is believed to have come into existence as a
result of the volcanic expulsion of substances from its interior, mainlyresult of the volcanic expulsion of substances from its interior, mainly
water vapour, with some carbon dioxide, nitrogen and sulphur. Thewater vapour, with some carbon dioxide, nitrogen and sulphur. The
atmosphere can only hold a certain amount of water vapour, so the excessatmosphere can only hold a certain amount of water vapour, so the excess
condensed into liquid water to form the oceans.condensed into liquid water to form the oceans.
It is thought that the first stage in the evolution of life on Earth requiredIt is thought that the first stage in the evolution of life on Earth required
an oxygen-free environment. Later primitive forms of plant life developedan oxygen-free environment. Later primitive forms of plant life developed
in the oceans and began to release small amounts of oxygen into thein the oceans and began to release small amounts of oxygen into the
atmosphere as a waste product from the cycle of photosynthesis: H2O +atmosphere as a waste product from the cycle of photosynthesis: H2O +
CO2 + sunlight sugar + O→CO2 + sunlight sugar + O→ 22
This build-up of atmospheric oxygen eventually led to the formation of theThis build-up of atmospheric oxygen eventually led to the formation of the
ozone layer. This layer, approximately 8 to 30 km above the surface, helpsozone layer. This layer, approximately 8 to 30 km above the surface, helps
to filter the ultraviolet portion of the incoming solar radiation. Therefore,to filter the ultraviolet portion of the incoming solar radiation. Therefore,
as levels of harmful ultraviolet radiation decreased, so plants were able toas levels of harmful ultraviolet radiation decreased, so plants were able to
move to progressively higher levels in the oceans.move to progressively higher levels in the oceans.
This helped to boost photosynthesis and thereby the production of oxygen.This helped to boost photosynthesis and thereby the production of oxygen.
Today, this element has reached levels where life has been sustainable onToday, this element has reached levels where life has been sustainable on
the surface of the planet through its presence, and it should bethe surface of the planet through its presence, and it should be
remembered that oxygen is an element which is not commonly found inremembered that oxygen is an element which is not commonly found in
the universe.the universe.

6. Composition of theComposition of the atmosphereatmosphere
Main Elements = 99%Main Elements = 99%
Nitrogen (NNitrogen (N22)) 78%78%
Oxygen (0Oxygen (022)) 21%21%
Trace Elements = 1%Trace Elements = 1% Xenon (Xe)Xenon (Xe)
Argon (Ar)Argon (Ar) Ozone (OOzone (O33))
Carbon Dioxide (COCarbon Dioxide (CO22)) Nitrogen Dioxide (NONitrogen Dioxide (NO22))
Neon (Ne)Neon (Ne) Iodine (I)Iodine (I)
Helium (He)Helium (He) Carbon Monoxide (CO)Carbon Monoxide (CO)
Methane (CHMethane (CH44)) Ammonia (NHAmmonia (NH33))
Nitrous Oxide (NNitrous Oxide (N22O)O) Water Vapour (HWater Vapour (H220)0)

7. Vertical structure of the atmosphereVertical structure of the atmosphere
The atmosphere is dividedThe atmosphere is divided
intointo fourfour isothermal layers orisothermal layers or
'spheres':'spheres': troposphere,troposphere,
stratosphere, mesospherestratosphere, mesosphere
and thermosphere.and thermosphere.
Each layer is characterised byEach layer is characterised by
a uniform change ina uniform change in
temperature with increasingtemperature with increasing
altitude.altitude.
In some layers there is anIn some layers there is an
increase in temperature withincrease in temperature with
altitude, whilst in others italtitude, whilst in others it
decreases with increasingdecreases with increasing
altitude.altitude.
The top or boundary of eachThe top or boundary of each
layer is denoted by a 'pause'layer is denoted by a 'pause'
where the temperature profilewhere the temperature profile
abruptly changesabruptly changes ..

8. TroposphereTroposphere
The troposphere contains aboutThe troposphere contains about 80%80% of the atmosphere and isof the atmosphere and is
the part of the atmosphere in which we live, and makethe part of the atmosphere in which we live, and make
weather observations.weather observations.
In this layer, average temperatures decrease with heightIn this layer, average temperatures decrease with height
6.46.4oo
c/1000m, as there is less air in contact with the ground toc/1000m, as there is less air in contact with the ground to
heat up. This is known asheat up. This is known as Environmental Lapse rateEnvironmental Lapse rate (adiabatic(adiabatic
cooling brought about by changes in temperature caused by acooling brought about by changes in temperature caused by a
decrease in pressure at height).decrease in pressure at height).
This sphere mixes vertically by convection, conduction andThis sphere mixes vertically by convection, conduction and
turbulence more than any other sphere. These vertical motionsturbulence more than any other sphere. These vertical motions
and the abundance of water vapour make it the home of alland the abundance of water vapour make it the home of all
important weather phenomena.important weather phenomena.
The troposphere is aroundThe troposphere is around 16 km high16 km high at the equator, with theat the equator, with the
temperature at the tropopause around –80 °C. At the poles,temperature at the tropopause around –80 °C. At the poles,
the troposphere reaches a height of around 8 km, with thethe troposphere reaches a height of around 8 km, with the
temperature of the tropopause around –40 °C in summer and –temperature of the tropopause around –40 °C in summer and –
60 °C in winter. Therefore, despite the higher surface60 °C in winter. Therefore, despite the higher surface
temperatures, the tropical tropopause is much cooler than attemperatures, the tropical tropopause is much cooler than at
the poles at the thickness is increased – more cooling occurs.the poles at the thickness is increased – more cooling occurs.

9. StratosphereStratosphere
Temperatures in the stratosphere rise with increasingTemperatures in the stratosphere rise with increasing
altitude (creating a temperature inversion) this isaltitude (creating a temperature inversion) this is
caused by concentrations on Ocaused by concentrations on O33 which absorbswhich absorbs
ultraviolet radiation. This is greatest around 50 km atultraviolet radiation. This is greatest around 50 km at
the edge of the stratopause. Temperatures range from –the edge of the stratopause. Temperatures range from –
30 °C over the winter pole to +20 °C over the summer30 °C over the winter pole to +20 °C over the summer
pole according to latitude and season.pole according to latitude and season.
As well as a noticeable change in temperature, theAs well as a noticeable change in temperature, the
move from the troposphere into the stratosphere is alsomove from the troposphere into the stratosphere is also
marked by an abrupt change in the concentrations ofmarked by an abrupt change in the concentrations of
the variable trace elements. Water vapour decreasesthe variable trace elements. Water vapour decreases
sharply, whilst ozone concentrations increase. Thesesharply, whilst ozone concentrations increase. These
strong contrasts in concentrations are a reflection ofstrong contrasts in concentrations are a reflection of
little mixing between the moist, ozone-poorlittle mixing between the moist, ozone-poor
troposphere and the dry, ozone-rich stratosphere.troposphere and the dry, ozone-rich stratosphere.
The stratosphere extends up to around 48 km above theThe stratosphere extends up to around 48 km above the
surface, and together with the troposphere, theysurface, and together with the troposphere, they
account for 99.9% of the Earth's atmosphere.account for 99.9% of the Earth's atmosphere.

10. MesosphereMesosphere
Temperatures in the mesosphere decreaseTemperatures in the mesosphere decrease
rapidly as there is no water vapour, cloud, dustrapidly as there is no water vapour, cloud, dust
or ozone to absorb incoming radiation.or ozone to absorb incoming radiation.
Temperatures at the mesopause go as low as –Temperatures at the mesopause go as low as –
120 °C with very strong winds – 3000km/hr.120 °C with very strong winds – 3000km/hr.
As in the troposphere, the unstable profile meansAs in the troposphere, the unstable profile means
that vertical motions are not inhibited. Duringthat vertical motions are not inhibited. During
the summer, there is enough lifting to producethe summer, there is enough lifting to produce
clouds in the upper mesosphere at high latitudesclouds in the upper mesosphere at high latitudes

11. ThermosphereThermosphere
The thermosphere extends upwards to altitudes ofThe thermosphere extends upwards to altitudes of
several hundred kilometres, where temperaturesseveral hundred kilometres, where temperatures
range from 250range from 250oo
c to as high as 1,700c to as high as 1,700oo
c, getting warmerc, getting warmer
with increasing height.with increasing height.
Temperature ranges depend on the degree of solarTemperature ranges depend on the degree of solar
activity and as there is more atomic oxygen there (likeactivity and as there is more atomic oxygen there (like
ozone) to absorb the heat.ozone) to absorb the heat.
The temperature changes between day and nightThe temperature changes between day and night
((DiurnalDiurnal) amount to hundreds of degrees.) amount to hundreds of degrees.
Above 500 km temperatures are very difficult toAbove 500 km temperatures are very difficult to
define. Molecules are so widely spaced that they movedefine. Molecules are so widely spaced that they move
independently, and there is no reason why theirindependently, and there is no reason why their
temperatures should be the same.temperatures should be the same.

12. EarthEarth’’s Annual Heat Budgets Annual Heat Budget
– Heating of the Atmosphere– Heating of the Atmosphere
At ‘A’ the sun’s energy is
more concentrated on a
small land area – intense
heating.
At ‘B’ the sun’s energy is
spread over a wider
surface area – leading to
less direct heating.
‘A’‘B’ ‘B’

13. Heat Budget in OUR WinterHeat Budget in OUR Winter
In the
North in
OUR Winter
there is a
deficit
In the
South in
OUR Winter
there is a
surplus
At the
equator
there is a
surplus
Of course the Earth’s heat
budget is not that simple!
You have to remember the
effects of seasonality –
the seasonal shift in the
trace of the sun on the
Earth’s surface during it’s
orbit.

14. Heat Budget in OUR SummerHeat Budget in OUR Summer
In the South
in OUR
Summer
there is a
deficit
In the North
in OUR
Summer
there is a
surplus
At the
equator
there is a
surplus

15. EarthEarth’’s Annual Heat Budgets Annual Heat Budget
So over the pattern of a year the Earth’s heat budget changes with
the seasons, however there is always a surplus at the equator.
The uneven distribution of heating
across the Earth is what drives the
air to move (WIND) in an effort to
redistribute the heat to areas of
deficit.