STRUCTURE OF THE ATMOSPHERE

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

2. DefinitionsDefinitions

Weather – day to day changes in Weather – day to day changes in
the state of the atmosphere.the state of the atmosphere.

Climate – average weather Climate – average weather
conditions over a longer period of conditions 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 gaseous An atmosphere is defined as the gaseous
envelope that surrounds a celestial body.envelope that surrounds a celestial body.
Therefore, the Earth, like other planets in Therefore, the Earth, like other planets in
the solar system, has an atmosphere, which the solar system, has an atmosphere, which
is retained by gravitational attraction and is 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 the Learning about different states of the
atmosphere enables science to understand atmosphere 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 studies Meteorology is the subject that studies
the chemical and physical properties of the chemical and physical properties of
the atmosphere together with its fields of the 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 was At 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 a probably no atmosphere. It is believed to have come into existence as a
result of the volcanic expulsion of substances from its interior, mainly result of the volcanic expulsion of substances from its interior, mainly
water vapour, with some carbon dioxide, nitrogen and sulphur. The water vapour, with some carbon dioxide, nitrogen and sulphur. The
atmosphere can only hold a certain amount of water vapour, so the excess atmosphere 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 required It is thought that the first stage in the evolution of life on Earth required
an oxygen-free environment. Later primitive forms of plant life developed an oxygen-free environment. Later primitive forms of plant life developed
in the oceans and began to release small amounts of oxygen into the in 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 the This build-up of atmospheric oxygen eventually led to the formation of the
ozone layer. This layer, approximately 8 to 30 km above the surface, helps ozone 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 to as 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 on Today, this element has reached levels where life has been sustainable on
the surface of the planet through its presence, and it should be the surface of the planet through its presence, and it should be
remembered that oxygen is an element which is not commonly found in remembered that oxygen is an element which is not commonly found in
the universe. the universe.

6. Composition of the Composition of the atmosphereatmosphere
Main Elements = 99%Main Elements = 99%
Nitrogen (NNitrogen (N
22)) 78%78%
Oxygen (0Oxygen (0
22)) 21%21%
Trace Elements = 1%Trace Elements = 1%Xenon (Xe)Xenon (Xe)
Argon (Ar)Argon (Ar) Ozone (OOzone (O
33))
Carbon Dioxide (COCarbon Dioxide (CO
22))Nitrogen Dioxide (NONitrogen Dioxide (NO
22))
Neon (Ne)Neon (Ne) Iodine (I)Iodine (I)
Helium (He)Helium (He) Carbon Monoxide (CO)Carbon Monoxide (CO)
Methane (CHMethane (CH
44)) Ammonia (NHAmmonia (NH
33))
Nitrous Oxide (NNitrous Oxide (N
22O)O)Water Vapour (HWater Vapour (H
220)0)

7. Vertical structure of the atmosphereVertical structure of the atmosphere
The atmosphere is divided The atmosphere is divided
into into fourfour isothermal layers or isothermal layers or
'spheres': 'spheres': troposphere, troposphere,
stratosphere, mesosphere stratosphere, mesosphere
and thermosphere.and thermosphere.
Each layer is characterised by Each layer is characterised by
a uniform change in a uniform change in
temperature with increasing temperature with increasing
altitude.altitude.
In some layers there is an In some layers there is an
increase in temperature with increase in temperature with
altitude, whilst in others it altitude, whilst in others it
decreases with increasing decreases with increasing
altitude.altitude.
The top or boundary of each The top or boundary of each
layer is denoted by a 'pause' layer is denoted by a 'pause'
where the temperature profile where the temperature profile
abruptly changesabruptly changes . .

8. TroposphereTroposphere
The troposphere contains about The troposphere contains about 80%80% of the atmosphere and is of the atmosphere and is
the part of the atmosphere in which we live, and make the part of the atmosphere in which we live, and make
weather observations.weather observations.
In this layer, average temperatures decrease with height In this layer, average temperatures decrease with height
6.46.4
oo
c/1000m, as there is less air in contact with the ground to c/1000m, as there is less air in contact with the ground to
heat up. This is known as heat up. This is known as Environmental Lapse rate Environmental Lapse rate (adiabatic (adiabatic
cooling brought about by changes in temperature caused by a cooling 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 and This sphere mixes vertically by convection, conduction and
turbulence more than any other sphere. These vertical motions turbulence more than any other sphere. These vertical motions
and the abundance of water vapour make it the home of all and the abundance of water vapour make it the home of all
important weather phenomena.important weather phenomena.
The troposphere is around The troposphere is around 16 km high16 km high at the equator, with the at 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 the the 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 surface 60 °C in winter. Therefore, despite the higher surface
temperatures, the tropical tropopause is much cooler than at temperatures, 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 increasing Temperatures in the stratosphere rise with increasing
altitude (creating a temperature inversion) this is altitude (creating a temperature inversion) this is
caused by concentrations on Ocaused by concentrations on O
33 which absorbs which absorbs
ultraviolet radiation. This is greatest around 50 km at ultraviolet 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 summer 30 °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, the As well as a noticeable change in temperature, the
move from the troposphere into the stratosphere is also move from the troposphere into the stratosphere is also
marked by an abrupt change in the concentrations of marked by an abrupt change in the concentrations of
the variable trace elements. Water vapour decreases the variable trace elements. Water vapour decreases
sharply, whilst ozone concentrations increase. These sharply, whilst ozone concentrations increase. These
strong contrasts in concentrations are a reflection of strong contrasts in concentrations are a reflection of
little mixing between the moist, ozone-poor little 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 the The stratosphere extends up to around 48 km above the
surface, and together with the troposphere, they surface, 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 decrease Temperatures in the mesosphere decrease
rapidly as there is no water vapour, cloud, dust rapidly 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 means As in the troposphere, the unstable profile means
that vertical motions are not inhibited. During that vertical motions are not inhibited. During
the summer, there is enough lifting to produce the 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 of The thermosphere extends upwards to altitudes of
several hundred kilometres, where temperatures several hundred kilometres, where temperatures
range from 250range from 250
oo
c to as high as 1,700c to as high as 1,700
oo
c, getting warmer c, getting warmer
with increasing height.with increasing height.
Temperature ranges depend on the degree of solar Temperature ranges depend on the degree of solar
activity and as there is more atomic oxygen there (like activity 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 night The temperature changes between day and night
((DiurnalDiurnal) amount to hundreds of degrees. ) amount to hundreds of degrees.
Above 500 km temperatures are very difficult to Above 500 km temperatures are very difficult to
define. Molecules are so widely spaced that they move define. Molecules are so widely spaced that they move
independently, and there is no reason why their independently, and there is no reason why their
temperatures should be the same. temperatures should be the same.

12. EarthEarth’’s Annual Heat Budget s 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.