Lecture 3: Lecture 3: RadiationRadiation and Earth’s Atmosphere and Earth’s AtmosphereEarthsClimate_Web_Chapter.pdf, p. 1-5

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Earth’s AtmosphereEarth’s Atmosphere

1. What is it?

A thin gaseous envelope around the planet.

2. Composition Today’s atmosphere: nitrogen (78%), oxygen

(21%), other (1%) – trace gases!

Nitrogen, oxygen, argon, water vapor, carbon dioxide, methane, Nitrogen, oxygen, argon, water vapor, carbon dioxide, methane, and most other gases are invisible.and most other gases are invisible.

Clouds are not gas, but condensed vapor in the form Clouds are not gas, but condensed vapor in the form of liquid droplets or ice particles.of liquid droplets or ice particles.

Ground based smog, which is visible, contains Ground based smog, which is visible, contains reactants of nitrogen and ozone.reactants of nitrogen and ozone.

3. Structure Four Four layers: layers: TroposphereTroposphere

(overturning(overturning) )

StratosphereStratosphere (stratified) (stratified)

From surface to 8-18 kmFrom surface to 8-18 km

From troposphere top to 50 From troposphere top to 50 kmkmMesosphereMesosphere

ThermosphereThermosphere

Blue sky!

The Structure of Earth’s AtmosphereThe Structure of Earth’s Atmosphere

1. Four layers defined by

temperature

2. Importance to climate and climate change

Troposphere:

Troposphere:Stratosphere:Mesosphere:Thermosphere:

T decreases with elevationT increases with elevationT decreases with elevationT increases with elevation

80% of Earth’s gases 80% of Earth’s gases

Most of Earth’s weather happensMost of Earth’s weather happens

Most of the measurementsMost of the measurements

Stratosphere:

19.9% of Earth’s gases 19.9% of Earth’s gases

Ozone layer: Ozone layer:

Blocking Sun’s ultraviolet Blocking Sun’s ultraviolet radiationradiation

Energy from the SunEnergy from the Sun

1. Characteristics

Travels through space (vacuum) in a speed of light

3. Importance to climate and climate change

In the form of waves:

In stream of particles

Electromagnetic waves

(Photons)

Primary driving force of Earth’s climate Primary driving force of Earth’s climate engineengine

2. Electromagnetic spectrum

From short wavelength, high energy, gamma rays to long wavelength, low energy, radio waves

Releases heat when absorbed

Ultraviolet, Visible, InfraredUltraviolet, Visible, Infrared

Sun’s Electromagnetic SpectrumSun’s Electromagnetic Spectrum

Solar radiation has peak intensities in the Solar radiation has peak intensities in the shorter wavelengthsshorter wavelengths, , dominant in the region we know as dominant in the region we know as visiblevisible, thus , thus shortwave shortwave radiationradiation

Blackbody Radiation Curves

Any object above Any object above absolute zero absolute zero radiates heat, radiates heat, as as proportional to proportional to TT44

Higher temperature, Higher temperature, shorter wavelengthshorter wavelength

Longwave & Shortwave RadiationLongwave & Shortwave Radiation

The The hot sunhot sun radiates at radiates at shortershorter wavelengths wavelengths that carry that carry more more energyenergy, and the , and the fraction fraction absorbed by the absorbed by the cooler earthcooler earth is is then re-radiated then re-radiated at at longer longer wavelengths.wavelengths.

Atmospheric Greenhouse EffectsAtmospheric Greenhouse Effects

T= 15°C (59°F)

T= –18°C (0°F)

Greenhouse effects make Earth’s surface warmer!Greenhouse effects make Earth’s surface warmer!

Surface Temperature With the Atmosphere

Surface Temperature Without the Atmosphere

Water vapor accounts for 60% of the atmospheric greenhouse effect, CO2 26%, and the remaining greenhouse gases 14%.

Greenhouse Gases

Water vapor (H2O)

Carbon dioxide (CO2) Methane (CH4)

Nitrous oxide (N2O)Ozone (O3)Chlorofluorocarbons

(CFC’s)

What are they?

CO2 contributes most (55-60%) to the anthropogenic greenhouse effect, and methane is a distant second (16%).

CFCs cause the strongest greenhouse warming on a molecule-for-molecule basis.

Atmospheric AbsorptionAtmospheric Absorption

Solar radiation Solar radiation passes passes rather freelyrather freely through through Earth's atmosphere.Earth's atmosphere.

Earth emits longwave Earth emits longwave energy, which either fits energy, which either fits through a through a narrow narrow windowwindow or or

is is absorbedabsorbed by by greenhouse gases and greenhouse gases and radiated back to Earth.radiated back to Earth.

Wavelength

Abs

orpt

ion

(100

%)

Nitrous Oxide

Methane

Ozone

Water Vapor

Carbon Dioxide

Total Atmo

IR

UV

Solar Intensity and LatitudeSolar Intensity and Latitude

Solar intensity, defined as the Solar intensity, defined as the energy per areaenergy per area, is different at , is different at different latitude.different latitude.

A sunlight beam that A sunlight beam that strikes at an anglestrikes at an angle is is spreadspread across a greater across a greater surface area, and is a surface area, and is a less intenseless intense heat source than a beam heat source than a beam impinging directly.impinging directly.

Unequal Radiation on a SphereUnequal Radiation on a Sphere

Insolation is stronger in the tropics (low latitudes) than in in the polar regions (high latitudes).

Pole-to-Equator Heating ImbalancesPole-to-Equator Heating Imbalances

What controls the elevation of the Sun above the horizon?What controls the elevation of the Sun above the horizon?

Earth’s Tilt Primarily Determines SeasonEarth’s Tilt Primarily Determines Season

Earth's Annual Energy BalanceEarth's Annual Energy Balance

The The balancebalance is is achieved locally achieved locally at at only two linesonly two lines of latitude.of latitude.

A A global balanceglobal balance is maintained by is maintained by excess excess heatheat from from the equatorial the equatorial region region transferringtransferring toward the toward the poles.poles.

Incoming Solar Radiation

Outgoing Longwave Radiation

Unequal heating of tropics and polesUnequal heating of tropics and poles

The Global Energy Budget: Driver of Atmospheric Motion

However, the tilt of theEarth means this balanceis not maintained for eachlatitude

A balance exists between the incoming solar andoutgoing longwave energy averaged over the globe and the year

DEFICITSURPLUS