Lesson 1Lesson 1

Structure of the Structure of the AtmosphereAtmosphere

Specification: Major climate controls

DefinitionsDefinitions

Weather – day to day Weather – day to day changes in the state of the changes in the state of the atmosphere.atmosphere.

Climate – average weather Climate – average weather conditions over a longer conditions over a longer period of time – 30 years.period of time – 30 years.

What is the Atmosphere?What is the Atmosphere?

An atmosphere is defined as the An atmosphere is defined as the gaseous envelope that surrounds a gaseous envelope that surrounds a celestial body.celestial body.

Therefore, the Earth, like other planets Therefore, the Earth, like other planets in the solar system, has an atmosphere, in the solar system, has an atmosphere, which is retained by gravitational which is retained by gravitational attraction and largely rotates with it. attraction and largely rotates with it.

Who studies the Who studies the Atmosphere?Atmosphere?

Learning about different states of the Learning about different states of the atmosphere enables science to atmosphere enables science to understand and predict changes on a understand and predict changes on a range of scales. range of scales.

Meteorology is the subject that Meteorology is the subject that studies the chemical and physical studies the chemical and physical properties of the atmosphere properties of the atmosphere together with its fields of motion, together with its fields of motion, mass and moisturemass and moisture. .

How was is formed?How was is formed?At the time of the Earth's formation around 4.5 billion years ago 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 there was probably no atmosphere. It is believed to have come into existence as a result of the volcanic expulsion of substances into existence as a result of the volcanic expulsion of substances from its interior, mainly water vapour, with some carbon dioxide, from its interior, mainly water vapour, with some carbon dioxide, nitrogen and sulphur. The atmosphere can only hold a certain nitrogen and sulphur. The atmosphere can only hold a certain amount of water vapour, so the excess condensed into liquid water amount of water vapour, so the excess condensed into liquid water to form the oceans. to form the oceans.

It is thought that the first stage in the evolution of life on Earth It is thought that the first stage in the evolution of life on Earth required an oxygen-free environment. Later primitive forms of required an oxygen-free environment. Later primitive forms of plant life developed in the oceans and began to release small plant life developed in the oceans and began to release small amounts of oxygen into the atmosphere as a waste product from amounts of oxygen into the atmosphere as a waste product from the cycle of photosynthesis: H2O + CO2 + sunlight → sugar + Othe cycle of photosynthesis: H2O + CO2 + sunlight → sugar + O22

This build-up of atmospheric oxygen eventually led to the This build-up of atmospheric oxygen eventually led to the formation of the ozone layer. This layer, approximately 8 to 30 km formation of the ozone layer. This layer, approximately 8 to 30 km above the surface, helps to filter the ultraviolet portion of the above the surface, helps to filter the ultraviolet portion of the incoming solar radiation. Therefore, as levels of harmful ultraviolet incoming solar radiation. Therefore, as levels of harmful ultraviolet radiation decreased, so plants were able to move to progressively radiation decreased, so plants were able to move to progressively higher levels in the oceans. higher levels in the oceans.

This helped to boost photosynthesis and thereby the production of This helped to boost photosynthesis and thereby the production of oxygen. Today, this element has reached levels where life has oxygen. Today, this element has reached levels where life has been sustainable on the surface of the planet through its been sustainable on the surface of the planet through its presence, and it should be remembered that oxygen is an element presence, and it should be remembered that oxygen is an element which is not commonly found in the universe. which is not commonly found in the universe.

Composition of the Composition of the atmosphereatmosphere

Main Elements = 99%Main Elements = 99%

Nitrogen (NNitrogen (N22)) 78%78%

Oxygen (0Oxygen (022)) 21%21%

Trace Elements Trace Elements = 1%= 1%

Xenon (Xe)Xenon (Xe)

Argon (Ar)Argon (Ar) Ozone (OOzone (O33))

Carbon Dioxide Carbon Dioxide (CO(CO22))

Nitrogen Dioxide Nitrogen Dioxide (NO(NO22))

Neon (Ne)Neon (Ne) Iodine (I)Iodine (I)

Helium (He)Helium (He) Carbon Monoxide Carbon Monoxide (CO)(CO)

Methane (CHMethane (CH44)) Ammonia (NHAmmonia (NH33))

Nitrous Oxide Nitrous Oxide (N(N22O)O)

Water Vapour (HWater Vapour (H220)0)

Vertical structure of the Vertical structure of the atmosphereatmosphere The atmosphere is divided The atmosphere is divided

into into fourfour isothermal layers isothermal layers or 'spheres': or 'spheres': troposphere, troposphere, stratosphere, stratosphere, mesosphere and mesosphere and thermosphere.thermosphere.

Each layer is characterised Each layer is characterised by a uniform change in by a uniform change in temperature with temperature with increasing altitude.increasing altitude.

In some layers there is an In some layers there is an increase in temperature increase in temperature with altitude, whilst in with altitude, whilst in others it decreases with others it decreases with increasing altitude.increasing altitude.

The top or boundary of The top or boundary of each layer is denoted by a each layer is denoted by a 'pause' where the 'pause' where the temperature profile temperature profile abruptly changesabruptly changes . .

TroposphereTroposphereThe troposphere contains about The troposphere contains about 80%80% of the atmosphere of the atmosphere and is the part of the atmosphere in which we live, and and is the part of the atmosphere in which we live, and make weather observations.make weather observations.

In this layer, average temperatures decrease with height In this layer, average temperatures decrease with height 6.46.4ooc/1000m, as there is less air in contact with the c/1000m, as there is less air in contact with the ground to heat up. This is known as ground to heat up. This is known as Environmental Environmental Lapse rate Lapse rate (adiabatic cooling brought about by changes (adiabatic cooling brought about by changes in temperature caused by a decrease in pressure at in temperature caused by a decrease in pressure at height).height).

This sphere mixes vertically by convection, conduction This sphere mixes vertically by convection, conduction and turbulence more than any other sphere. These and turbulence more than any other sphere. These vertical motions and the abundance of water vapour make vertical motions and the abundance of water vapour make it the home of all important weather phenomena.it the home of all important weather phenomena.

The troposphere is around The troposphere is around 16 km high16 km high at the equator, at the equator, with the temperature at the tropopause around –80 °C. At with the temperature at the tropopause around –80 °C. At the poles, the troposphere reaches a height of around 8 the poles, the troposphere reaches a height of around 8 km, with the temperature of the tropopause around –40 km, with the temperature of the tropopause around –40 °C in summer and –60 °C in winter. Therefore, despite the °C in summer and –60 °C in winter. Therefore, despite the higher surface temperatures, the tropical tropopause is higher surface temperatures, the tropical tropopause is much cooler than at the poles at the thickness is much cooler than at the poles at the thickness is increased – more cooling occurs.increased – more cooling occurs.

StratosphereStratosphereTemperatures in the stratosphere rise with Temperatures in the stratosphere rise with increasing altitude (creating a temperature increasing altitude (creating a temperature inversion) this is caused by concentrations on Oinversion) this is caused by concentrations on O33 which absorbs ultraviolet radiation. This is greatest which absorbs ultraviolet radiation. This is greatest around 50 km at the edge of the stratopause. around 50 km at the edge of the stratopause. Temperatures range from –30 °C over the winter Temperatures range from –30 °C over the winter pole to +20 °C over the summer pole according to pole to +20 °C over the summer pole according to latitude and season. 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 move from the troposphere into the stratosphere is also marked by an abrupt change in the also marked by an abrupt change in the concentrations of the variable trace elements. concentrations of the variable trace elements. Water vapour decreases sharply, whilst ozone Water vapour decreases sharply, whilst ozone concentrations increase. These strong contrasts in concentrations increase. These strong contrasts in concentrations are a reflection of little mixing concentrations are a reflection of little mixing between the moist, ozone-poor troposphere and the between the moist, ozone-poor troposphere and the dry, ozone-rich stratosphere. dry, ozone-rich stratosphere.

The stratosphere extends up to around 48 km above The stratosphere extends up to around 48 km above the surface, and together with the troposphere, they the 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.

MesosphereMesosphere

Temperatures in the mesosphere decrease Temperatures in the mesosphere decrease rapidly as there is no water vapour, cloud, rapidly as there is no water vapour, cloud, dust or ozone to absorb incoming radiation.dust or ozone to absorb incoming radiation.

Temperatures at the mesopause go as low Temperatures at the mesopause go as low as –120 °C with very strong winds – as –120 °C with very strong winds – 3000km/hr.3000km/hr.

As in the troposphere, the unstable profile As in the troposphere, the unstable profile means that vertical motions are not means that vertical motions are not inhibited. During the summer, there is inhibited. During the summer, there is enough lifting to produce clouds in the enough lifting to produce clouds in the upper mesosphere at high latitudesupper mesosphere at high latitudes

ThermosphereThermosphereThe thermosphere extends upwards to altitudes The thermosphere extends upwards to altitudes of several hundred kilometres, where of several hundred kilometres, where temperatures range from 250temperatures range from 250ooc to as high as c to as high as 1,7001,700ooc, getting warmer with increasing height.c, getting warmer with increasing height.

Temperature ranges depend on the degree of Temperature ranges depend on the degree of solar activity and as there is more atomic solar activity and as there is more atomic oxygen there (like ozone) to absorb the heat. oxygen there (like ozone) to absorb the heat.

The temperature changes between day and The temperature changes between day and night (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 define. Molecules are so widely spaced that they move independently, and there is no reason why move independently, and there is no reason why their temperatures should be the same. their temperatures should be the same.

EarthEarth’’s Annual Heat s Annual Heat Budget – Heating of the Budget – Heating of the

Atmosphere 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 ’

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.

Heat Budget in OUR Heat Budget in OUR SummerSummer

In the South in

OUR Summer there is a

deficit

In the North in

OUR Summer there is a surplusAt the

equator there is a surplus

EarthEarth’’s Annual Heat s Annual Heat BudgetBudgetSo 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.