Elements%20of%20the%20Sun;%20Solar%20Radiation

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Lecture 3 Radiation and Earths Atmosphere
EarthsClimate_Web_Chapter.pdf, p. 1-5
For more advanced reading materials, please see
http//www.geo.utexas.edu/courses/387h/ScheduleGPC
_detail.htm
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Earths Atmosphere
1. What is it?
A thin gaseous envelope around the planet.
Blue sky!
2. Composition
Todays atmosphere nitrogen (78), oxygen
(21), other (1) trace gases!
Nitrogen, oxygen, argon, water vapor, carbon
dioxide, methane, and most other gases are
invisible.
Clouds are not gas, but condensed vapor in the
form of liquid droplets or ice particles.
Ground based smog, which is visible, contains
reactants of nitrogen and
ozone.
Four layers
3. Structure
Troposphere
(overturning)
From surface to 8-18 km
Stratosphere
(stratified)
From troposphere top to 50 km
Mesosphere
Thermosphere
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The Structure of Earths Atmosphere
1. Four layers defined by
temperature
Troposphere
T decreases with elevation
T increases with elevation
Stratosphere
Mesosphere
T decreases with elevation
Thermosphere
T increases with elevation
2. Importance to climate and climate change
Troposphere
80 of Earths gases
Most of Earths weather happens
Most of the measurements
Stratosphere
19.9 of Earths gases
Ozone layer
Blocking Suns ultraviolet radiation
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Energy from the Sun
1. Characteristics
Travels through space (vacuum)
in a speed of light
In the form of waves
Electromagnetic waves
(Photons)
In stream of particles
Releases heat when absorbed
2. Electromagnetic spectrum
From short wavelength, high energy, gamma rays to
long wavelength, low energy, radio waves
3. Importance to climate and climate change
Primary driving force of Earths climate engine
Ultraviolet, Visible, Infrared
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Suns Electromagnetic Spectrum
Solar radiation has peak intensities in the
shorter wavelengths, dominant in the region we
know as visible, thus shortwave radiation
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Blackbody Radiation Curves
Any object above absolute zero radiates heat, as
proportional to T4
Higher temperature, shorter wavelength
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Longwave Shortwave Radiation
The hot sun radiates at shorter wavelengths that
carry more energy, and the fraction absorbed by
the cooler earth is then re-radiated at longer
wavelengths.
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Atmospheric Greenhouse Effects
T 15C (59F)
Surface Temperature With the Atmosphere
T 18C (0F)
Surface Temperature Without the Atmosphere
Greenhouse effects make Earths surface warmer!
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Greenhouse Gases

• What are they?

Water vapor (H2O)
Carbon dioxide (CO2)
Methane (CH4)
Chlorofluorocarbons (CFCs)
Ozone (O3)
Nitrous oxide (N2O)

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

• 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.

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Nitrous Oxide
Atmospheric Absorption
Methane
Solar radiation passes rather freely through
Earth's atmosphere. Earth emits longwave energy,
which either fits through a narrow window or is
absorbed by greenhouse gases and radiated back to
Earth.
Ozone
Absorption (100)
Water Vapor
Carbon Dioxide
UV
IR
Total Atmo
Wavelength
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Solar Intensity and Latitude
Solar intensity, defined as the energy per area,
is different at different latitude. A sunlight
beam that strikes at an angle is spread across a
greater surface area, and is a less intense heat
source than a beam impinging directly.
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Unequal Radiation on a Sphere
Insolation is stronger in the tropics (low
latitudes) than in in the polar regions (high
latitudes).
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Pole-to-Equator Heating Imbalances
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What controls the elevation of the Sun above the
horizon?
Earths Tilt Primarily Determines Season
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Earth's Annual Energy Balance
The balance is achieved locally at only two lines
of latitude. A global balance is maintained by
excess heat from the equatorial region
transferring toward the poles.
Incoming Solar Radiation
Outgoing Longwave Radiation
Unequal heating of tropics and poles
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The Global Energy Budget Driver of Atmospheric
Motion
A balance exists between the incoming solar
and outgoing longwave energy averaged over the
globe and the year
However, the tilt of the Earth means this
balance is not maintained for each latitude
DEFICIT
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