AS Course

Module 3:THE ATMOSPHERE

• The atmosphere is heated from BELOW1. Solar energy hits the earth’s surface (short-wave) 2. The earth’s surface ABSORBS the short wave energy

from sun via CONDUCTION3. Also the air directly above the earth’s surface is also

heated by CONDUCTION4. 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 AtmosphereThe 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.

TroposphereThe 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.

MesosphereThe 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 constantSolar constant

• Distance from the sunDistance from the sun

• Angle of the sun in the skyAngle of the sun in the sky

• Seasonal variationsSeasonal variations

The amount The amount of energy of energy which is which is received received from the sun from the sun varies with varies with sunspot sunspot activity.activity.

Its exact Its exact value is not value is not known but is known but is about 1380W about 1380W mm22

The earth’s distance from the sun varies The earth’s distance from the sun varies throughout time and this can cause a 6% variation throughout time and this can cause a 6% variation in the solar constant. It has been argued that this in the solar constant. It has been argued that this has been enough to cause the ice ages. has been enough to cause the ice ages.

The curvature of the earth means that there is TWICE as much The curvature of the earth means that there is TWICE as much incoming solar radiation reaching the earth's surface at the incoming solar radiation reaching the earth's surface at the equator (during the autumn and spring equinox’s) than there is at equator (during the autumn and spring equinox’s) than there is at 606000N or SN or S

It is clear in this diagram It is clear in this diagram how much more land how much more land area the same “bundle” area the same “bundle” of solar radiation has to of solar radiation has to cover than that at the cover than that at the equatorequator

EARTHEARTH

EquatorEquator

SUNSUN

December 21stDecember 21st June 21stJune 21st

Earth’s Earth’s axis is on axis is on a 23.5a 23.500 tilt tilt

606000N. This is the N. This is the latitude of northern latitude of northern ScotlandScotland

Midsummer's day in the Midsummer's day in the Northern HemisphereNorthern Hemisphere

Midwinter's day in the Midwinter's day in the Northern HemisphereNorthern Hemisphere

EquatorEquator

The time of year makes an enormous difference to the amount of The time of year makes an enormous difference to the amount of radiation which reaches the earth’s surfaceradiation which reaches the earth’s surface

During the summer months when the Northern Hemisphere is tilted During the summer months when the Northern Hemisphere is tilted towards the sun, the angle at which the incoming solar radiation towards the sun, the angle at which the incoming solar radiation strikes the earth’s surface is high. The sun is directly over the Tropic strikes the earth’s surface is high. The sun is directly over the Tropic of Cancer, which is 23.5of Cancer, which is 23.50 0 NORTH of the equator. Consequently the NORTH of the equator. Consequently the summers in the N Hemisphere are hot. summers in the N Hemisphere are hot.

During the Northern Hemisphere winter, the angle at which the incoming During the Northern Hemisphere winter, the angle at which the incoming solar radiation reaches the surface is very low and each bundle of radiation solar radiation reaches the surface is very low and each bundle of radiation is having to heat a far larger area of land. The sun is directly overhead the is having to heat a far larger area of land. The sun is directly overhead the Tropic of Capricorn, which is 23.5Tropic of Capricorn, which is 23.50 0 SOUTH of the equator.SOUTH of the equator.

Consequently N Hemisphere winters are cold. Consequently N Hemisphere winters are cold.

The days are short during the winter and there is little time for the incoming The days are short during the winter and there is little time for the incoming solar radiation to heat the ground after the long nights. Note that the North solar radiation to heat the ground after the long nights. Note that the North Pole receives no insolation at all during this timePole receives no insolation at all during this time

The N Hemisphere summer days are long which means there is The N Hemisphere summer days are long which means there is more time for the ground to be heated by incoming solar more time for the ground to be heated by incoming solar radiation radiation

SUNSUN

March 21stMarch 21st

September 21stSeptember 21st

Earth’s Earth’s axis is on axis is on a 23.5a 23.500 tilt tilt

Autumn equinoxAutumn equinox

Spring equinoxSpring equinox

Twice during the Twice during the year the sun is year the sun is directly overhead directly overhead at the equator at the equator and the N and S and the N and S Hemispheres Hemispheres receive equal receive equal amounts of I S Ramounts of I S R

Consequently there is Consequently there is 12 hour night and 12 12 hour night and 12 hour day across the hour day across the entire globe, give or entire globe, give or take 15 minutestake 15 minutes

The sun is The sun is “sideways on” to “sideways on” to the earth and as the earth and as a result the tilt is a result the tilt is negated negated

For an excellent graphical explanation of the For an excellent graphical explanation of the seasons go to;seasons go to;

www.usatoday.com/weatherwww.usatoday.com/weather

Clouds clearly reduce the amount of ISR during the Clouds clearly reduce the amount of ISR during the day, but this doesn’t necessarily mean it will be colder!day, but this doesn’t necessarily mean it will be colder!

During the summer months it is warmer during the day During the summer months it is warmer during the day if there is no cloud, as all the ISR can reach the earths if there is no cloud, as all the ISR can reach the earths surface……….surface……….

However at NIGHT all the heat on the ground escapes However at NIGHT all the heat on the ground escapes into space as there are no clouds to hold it in…...into space as there are no clouds to hold it in…...As a result it is warmer at night when there is heavy As a result it is warmer at night when there is heavy cloud cover.cloud cover.Based on this information can you explain why it Based on this information can you explain why it is warmer in the day during the winter when is warmer in the day during the winter when there is cloud?there is cloud?

The picture is complicated further as it depends what The picture is complicated further as it depends what SORT OF CLOUDS are in the skySORT OF CLOUDS are in the sky

Cumulus clouds (the “fluffy” ones) reflect a lot of ISR due to Cumulus clouds (the “fluffy” ones) reflect a lot of ISR due to their light colour. their light colour.

This is due to the ALBEDO effect, which we will look at This is due to the ALBEDO effect, which we will look at later.later.

Stratus clouds on the other hand (Grey blanket cloud) are Stratus clouds on the other hand (Grey blanket cloud) are dark.dark.

These prevent longwave radiation leaving the lower These prevent longwave radiation leaving the lower atmosphere and can keep the environment WARMERatmosphere and can keep the environment WARMER

As a result of clouds, 23% of ISR never As a result of clouds, 23% of ISR never reaches the earth's surface. reaches the earth's surface.

20% is reflected and 3% is absorbed by the 20% is reflected and 3% is absorbed by the water droplets themselveswater droplets themselves

Consequently desert environments have the greatest Consequently desert environments have the greatest diurnal (day and night) variation and equatorial rainforests diurnal (day and night) variation and equatorial rainforests have the leasthave the least

3% absorbed by clouds

Earth’s albedo 30%

6% reflected / absorbed by atmosphere

20% reflected by clouds

4% reflected from earth’s surface

16% absorbed by dust and gases

• 16%is absorbed by atmospheric gases 16%is absorbed by atmospheric gases and dust. This is radiated as longwave and dust. This is radiated as longwave radiation which in turn warms the radiation which in turn warms the atmosphere. atmosphere.

•Much more (over 20%) incoming Much more (over 20%) incoming radiation is “scattered” by the gases and radiation is “scattered” by the gases and dust. This incoming radiation is then dust. This incoming radiation is then known as “diffuse radiation”.known as “diffuse radiation”.

•The remaining 6% is either absorbed by The remaining 6% is either absorbed by stratospheric ozone (O) or reflected by the stratospheric ozone (O) or reflected by the atmosphere. The proportion absorbed by atmosphere. The proportion absorbed by ozone is UV radiation, which is extremely ozone is UV radiation, which is extremely harmful to human skin and eyes (known to be harmful to human skin and eyes (known to be carcinogenic) as well as harmful to plantscarcinogenic) as well as harmful to plants

It is the absorption and scattering of It is the absorption and scattering of different wavelengths of ISR by gases and different wavelengths of ISR by gases and dust which cause the sky to be blue during dust which cause the sky to be blue during the day.the day.

Aurora borealis / australisAurora borealis / australis The northern / southern lightsThe northern / southern lights Thermosphere and uppermost MesosphereThermosphere and uppermost Mesosphere

– solar wind (clouds of electrically charged solar wind (clouds of electrically charged particles)particles)

– Earth’s magnetic field directs them towards Earth’s magnetic field directs them towards polespoles

– excite oxygen (O) and nitrogen (Nexcite oxygen (O) and nitrogen (N22) ions in ) ions in

ionosphere ionosphere emit light emit light

4% is reflected from the earth’s surface without being 4% is reflected from the earth’s surface without being absorbed. This is due to the ALBEDO effect which was absorbed. This is due to the ALBEDO effect which was mentioned earlier…….mentioned earlier…….

Different surfaces absorb and reflect varying amounts of Different surfaces absorb and reflect varying amounts of ISR. This is known as their albedo.ISR. This is known as their albedo.

Place the following surfaces in order, based on the amount Place the following surfaces in order, based on the amount of ISR they reflect. Have a guess at the amount of ISR they of ISR they reflect. Have a guess at the amount of ISR they reflectreflect

•Light coloured desertsLight coloured deserts

•Coniferous forestConiferous forest

•Fresh snowFresh snow

•Oceans and dark soilsOceans and dark soils

•Grassland and deciduous forestGrassland and deciduous forest

•Oceans and dark soilsOceans and dark soils <10% <10%

•Coniferous forest Coniferous forest 15%15%

•Grassland and deciduous forestGrassland and deciduous forest 25%25%

• Light coloured desertsLight coloured deserts 40%40%

•Fresh snowFresh snow 85%85%

The situation is further complicated by The situation is further complicated by the different ways in which the earth’s the different ways in which the earth’s surfaces heat and cool. This is obviously surfaces heat and cool. This is obviously a key factor when looking at climate as it a key factor when looking at climate as it is essentially the ground which heats the is essentially the ground which heats the atmosphere. atmosphere.

The way in which materials absorb and The way in which materials absorb and release heat energy is known as their release heat energy is known as their SPECIFIC HEAT CAPACITY. It is the SPECIFIC HEAT CAPACITY. It is the amount of energy required to raise 1kg of amount of energy required to raise 1kg of a substance by 1C.a substance by 1C.

Water and land are two clear examples of these Water and land are two clear examples of these variations.variations.

It requires 4.2kj of energy to heat 1kg of water by It requires 4.2kj of energy to heat 1kg of water by 1100C.C.

In comparison it takes only 2.1kj to heat 1kg of In comparison it takes only 2.1kj to heat 1kg of soil.soil.

Sand requires only 0.84kj.Sand requires only 0.84kj.

In layman's terms then, it takes twice In layman's terms then, it takes twice as much energy to heat water, BUT as much energy to heat water, BUT ALSO it needs to LOSE twice as much ALSO it needs to LOSE twice as much to cool down by the same amount.to cool down by the same amount.

As a result the oceans are cooler in the As a result the oceans are cooler in the summer but warmer in the winter and summer but warmer in the winter and are known as THERMAL RESERVOIRSare known as THERMAL RESERVOIRS

Being near a body of water therefore has a Being near a body of water therefore has a noticeable effect on the climate of a landmass as the noticeable effect on the climate of a landmass as the following slides demonstrate.following slides demonstrate.

404000 North North

Note the warm and the cold areas.Note the warm and the cold areas.

Any ideas as to why this is?Any ideas as to why this is?

Warm Warm CaribbeanCaribbean

Keeps Keeps inland inland areas areas warm in warm in winterwinter

Inland areas are far Inland areas are far from the sea and from the sea and away from the away from the warming influence warming influence of the Caribbeanof the Caribbean

404000 North North

404000 North North

Note how much farther Note how much farther north the UK is compared north the UK is compared to the latitude line.to the latitude line.

Any ideas as to why it Any ideas as to why it isn’t extremely cold?isn’t extremely cold?

(We are the same latitude (We are the same latitude in Bedford as Calgary in in Bedford as Calgary in Canada)Canada)

404000NorthNorth

GCM

The World

January 29th 2002

The World

January 29th 2002

Equatorial Low Pressure Equatorial Low Pressure Trough: Trough: Clouds and RainClouds and Rain

The Intertropical Convergence Zone (ITCZ)The Intertropical Convergence Zone (ITCZ) DoldrumsDoldrums

ITCZL

Subtropical High-Pressure Subtropical High-Pressure Cells: Cells:

Hot Desert AirHot Desert Air The Horse LatitudesThe Horse Latitudes Broad Cells of High Broad Cells of High

Pressure Pressure

H

AIR MASSES

Polar Maritime Air Mass

Unstable AirInstability is caused by an air mass rising off the ground. Thiscan be caused for example, by a body of cold air (in this case polar Maritime air) getting warmer as it moves further south – ieTowards 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.

Cold air begins to warm asIt travels further south thereforeRises off the ground – leadingTo UNSTABLE AIR

North Pole

EquatorUK

DEPRESSIONS

Atmospheric PressureAtmospheric PressurePressure can be thought of as Pressure can be thought of as

the weight of all overlying the weight of all overlying air (though, in reality, air (though, in reality, pressure exerts force in all pressure exerts force in all directions).directions).

Mercury BarometerMercury Barometer

- Invented by Toricelli, 1643- Invented by Toricelli, 1643

Average Sea Level Atmospheric Pressure:

29.92” of Mercury76 cm of Mercury1013 millibars (mb)

                                        

Warm Front

                                                                                                                                                                                                                                                                                      

Cold Front

Wa

rm a

ir

Co

ld Air

Wa

rm T

ropica

l M

aritim

e air

Co

ld Po

lar

Ma

ritime A

ir

WEATHER ASSOCIATED WITH THE PASSAGE OF A CLASSIC DEPRESSION

 Ahead of the warm

frontPassage of the

warm frontWarm 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 PressureAir PressureForce exerted by air molecules per unit areaForce exerted by air molecules per unit area

(Result of compression of the air by gravity).(Result of compression of the air by gravity).

This pressure force is omnidirectional.This pressure force is omnidirectional.

LOCAL ENERGY BUDGETS

Mountain-Mountain-ValleyValley

BreezesBreezes

Land and Sea BreezesLand and Sea Breezes

LH

x 5x

Temperature Temperature InversionsInversions

An upside-down An upside-down situationsituation

The ‘Normal’ SituationThe ‘Normal’ Situation

8’ 41°F16’ 41°F

32’ 40°F

64’ 40°F

105’ 38°F

8’ 41°F16’ 41°F

32’ 40°F

64’ 40°F

105’ 38°F

Temperature InversionsTemperature Inversions

These are when These are when the ‘normal’ the ‘normal’ situations are situations are reversed ie when reversed ie when warmer air warmer air overlies colder overlies colder air.air.

This can be at This can be at low low levellevel

Temperature InversionsTemperature Inversions

These are when These are when the ‘normal’ the ‘normal’ situations are situations are reversed ie when reversed ie when warmer air warmer air overlies colder air.overlies colder air.

This can be at This can be at low low levellevel or at or at high high levellevel

Temperature Temperature InversionsInversions

There is a natural There is a natural inversion in our inversion in our atmosphere as atmosphere as the stratosphere the stratosphere is the layer that is the layer that absorbs most of absorbs most of the ultraviolet the ultraviolet radiation (high radiation (high level)level)

Temperature InversionsTemperature Inversions High level inversions are also found in High level inversions are also found in

depressions, when the warm sector depressions, when the warm sector overlies the cold sector (occlusion)overlies the cold sector (occlusion)

Temperature InversionsTemperature Inversions Low level or ground Low level or ground

inversions occur in inversions occur in anticyclonic conditions anticyclonic conditions when there is a rapid when there is a rapid loss of energy at loss of energy at night.night.

The air near the The air near the surface is cooled by surface is cooled by conduction of heat to conduction of heat to the cold ground. The the cold ground. The lower layer is lower layer is therefore colder than therefore colder than the air above itthe air above it..

Temperature InversionsTemperature Inversions Low level or ground Low level or ground

inversions occur in inversions occur in anticyclonic conditions anticyclonic conditions when there is a rapid when there is a rapid loss of energy at loss of energy at night.night.

The air near the The air near the surface is cooled by surface is cooled by conduction of heat to conduction of heat to the cold ground. The the cold ground. The lower layer is lower layer is therefore colder than therefore colder than the air above itthe air above it..

Temperature InversionsTemperature Inversions A classic inversion is where the hot A classic inversion is where the hot

emissions given off by industrial emissions given off by industrial chimneys trap in the colder air belowchimneys trap in the colder air below

Signs of a surface inversion in the early morning Windless or light

variable wind

Ground Fog

Frost (or dew)

Lack of heavy cloud cover

Cold Air descends and condenses forming fog

HOT AIR – more able to carrymoisture

Smoke from a chimney forming a layer

Surface inversion - early morning