Announcements

1
Announcements
I will go over homework assignments for the
semester during the next two classes. TODAY
Writing assignment options assignment
lists WEDNESDAY Lab experiment demonstrations
by TAs FRIDAY Lab experiment kits
distributed I am in need of three notetakers
for students in the course. If you would be
willing to do this, please see me after class or
during office hours. You will receive
recognition for doing this from the DRC.
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Summary of Lecture 5
The three modes of heat transfer are conduction,
convection, and radiation. Radiation is energy
propagated by electromagnetic waves and is
emitted by all objects so long as they have a
temperature. The type of radiation an object
emits is dependent on its temperature. The
smaller the wavelength of radiation, the greater
the energy and the higher the temperature. The
entire range of radiation types is given by the
EM spectrum. The total radiant energy emitted by
an object is described by the Stefan-Boltzmann
law. The wavelength of maximum radiation
emission is described by Wiens law. Solar
radiation, or shortwave radiation, is that which
comes from the sun and is most intense in the
visible part of the spectrum. Terrestrial
radiation, or longwave radiation, is that which
comes from the Earth and is most intense in the
infrared part of the spectrum.
3
1st Review question from last lecture

• Given that the suns temperature is around 6000
  K, approximately what is the wavelength of
  maximum radiation emission?
• 5 10-3 m
• 5 10-4 m
• 5 10-5 m
• 5 10-6 m
• 5 10-7 m

4
2nd Review question from last lecture

• How much more energy per unit area is emitted
  from an object at 200 K vs. an object at 400 K?
• About 2 times more
• About 4 times more
• About 8 times more
• About 16 times more
• About 32 times more

5
NATS 101Section 6 Lecture 6

• The Greenhouse Effect and
• Earth-Atmosphere Energy Balance

6
Survey question
Thinking about the issue of global warming,
sometimes called the 'greenhouse effect,' how
well do you feel you understand this issue? Would
you say very well, fairly well, not very well, or
not at all? A) Very Well B) Fairly Well C)
Not Very Well D) Not at All E) I dont
understand the question.
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Gallup PollMarch 13-16, 2006
Thinking about the issue of global warming,
sometimes called the 'greenhouse effect,' how
well do you feel you understand this issue? Would
you say very well, fairly well, not very well, or
not at all? Very Well 21 Fairly Well
53 Not Very Well 20 Not at All 6
My comments as an atmospheric scientist Are the
greenhouse effect and global warming really the
same thing? If not, then NOBODY understands much
of anything wellincluding whoever wrote this
question!!
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• FOUR POSSIBLE FATES OF RADIATION
• 1.Transmitted
• 2. Reflected
• 3. Scattered
• 4. Absorbed
• The atmosphere does ALL of these

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Transmitted Radiation passes through object
GLASS WINDOW
SUNLIGHT
TRANSMITTED SUNLIGHT
10
Reflected Radiation turned back
REFLECTED SUNLIGHT
MIRROR
SUNLIGHT
11
Scattered Path of radiation deflected
SCATTERED SUNLIGHT
FROSTED GLASS
SUNLIGHT
12
Absorbed Radiation transferred to object
Blackbody a perfect absorber and emitter of
radiation in equilibrium, with no reflection or
scattering.
BLACK BOX
SUNLIGHT
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Radiative equilibrium Absorption Emission
(Kirchoffs Law)
INFRARED (LONGWAVE) EMISSION
BLACK BOX
SUNLIGHT (SHORTWAVE)
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A Grey Body Not all radiation absorbedHow
the atmosphere behaves
SOME TRANSMISSION OF SUNLIGHT THROUGH BOX
GREY BOX
SUNLIGHT (SHORTWAVE)
INFRARED (LONGWAVE) EMISSION
15
What Happens When Radiation is Absorbed?
Internal energy increases by changes on the
molecular and atomic levels ENERGY
TRANSITIONS Translational Rotational Vibration
al Electronic molecular Electronic atomic
Less Energy required Changes on molecular
level Longer wavelength of radiation
ENERGY REQUIRED
More energy required Changes on the atomic
level Shorter wavelength of radiation
16
Translational Energy
Gross movement of atoms and molecules through
space. The translational energy reflects the
kinetic energyand thus the temperature.
17
Rotational Energy
Energy associated the rotation of the molecule.
Takes on discrete values (or quanta) dependent on
the type of molecule. Corresponds to energy
changes shorter than 1 cm (far infrared).
Rotation of water molecules
Infrared photon
(Gedzelman 1980, p 105)
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Rotational Energy of Common Gases in the
Atmosphere
Molecules have rotational energy only if they
have a permanent dipole moment, or asymmetric
charge distribution.
(Hartmann 1994)
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Vibrational Energy
Molecular energy stored in the vibrations (or
stretching and bending) of atomic bonds. Takes
on discrete values (or quanta) dependent on the
type of molecule. Corresponds to energy changes
in the infrared spectrum.
Vibration of water molecules
Infrared photon
(Gedzelman 1980, p 105)
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Vibrational Energy for Common Gases in the
Atmosphere
Most effective absorbers are molecules that have
a dipole moment and/or are bent. Carbon
dioxide creates a dipole moment as a result of
its vibrational transitions, so has rotational
energy as well.
(Hartmann 1994)
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Electronic energy Photodissociation(Molecular
level)
Energy associated with breaking of atomic bonds
of molecules. Takes on discrete values (or
quanta) dependent on the type of molecule.
Corresponds mainly to energy changes in the
ultraviolet spectrum.
UV PHOTON
O
O
O
O
Oxygen molecule (O2)
Oxygen atoms (O)
22
Electronic energy Excitation(Atomic Level)
Energy associated with excitation of electrons in
the outer shell of an atom. Takes on discrete
values (or quanta) dependent on the type of
molecule. Corresponds to energy changes mainly in
the ultraviolet.
UV Photon
e-
e-
p
p
Hydrogen atom
Excited hydrogen atom
23
Electronic energy Ionization(Atomic level)
Energy associated with removal of electrons from
an atom. Takes on discrete values (or quanta)
dependent on the type of molecule. Corresponds
to energy changes mainly higher than ultraviolet.
Short wavelength UV or X-Ray photon
e-
e-
p
p
Hydrogen atom
Ionized hydrogen atom
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Flashback Why is there warming in Thermosphere
and Stratosphere?
THERMOSPHERE Warming because of ionization of
gases.
STRATOSPHERE Warming because of
photodissociation of ozone and oxygen.
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Aurora Borealis or Aurora Australis
Caused by ionization of gases in the Earths
atmosphere from the solar wind, which appears as
visible light. Occur only at the poles because
of the properties Earths magnetic field
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SOLAR
TERRESTRIAL
Absorption of Radiation by Common Atmospheric
Greenhouse Gases
The greenhouse gases are called such because
they absorb and emit very effectively in the
infrared band (5-20 µm) at selective
wavelengths. Water and CO2 are good greenhouse
gases Oxygen (O2) and ozone (O3) are absorbed in
the UV. Little or no absorption in some places
?max Sun
?max Earth
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Total Radiation Absorption Spectrum by all
Atmospheric Gases
SOLAR
TERRESTRIAL
Absorption
Little or no absorption.
A lot of absorption because of greenhouse gases,
except in an atmospheric window of 8-11 µm.
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Atmospheric Heating From Below
Since there is little or no absorption of
radiation in the most intense part of the solar
radiation band, the heat supplied comes from the
Earth itself.
LATENT HEATING
TERRESTRIAL RADIATION
SOLAR RADIATION
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Is the presence of the greenhouse gases in our
atmosphere good or bad?
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The Importance of the Greenhouse Effect
The presence of the gases in our atmosphere that
absorb and emit infrared radiation help maintain
the Earths average temperature at about 59 F.
Without these gases, ALL infrared radiation
from the Earths surface would be lost to space
and the Earth would be a frozen ice ball!
31
The Greenhouse Effect DOES NOT EQUAL Global
Warming or Climate Change!
Global warming The increase in Earths mean
temperature that would result because of the
increase in greenhouse gases due to human
activities. This would enhance the greenhouse
effect. Climate change Long-term change in
global, regional, or local climate resulting from
both enhanced greenhouse gases and/or other human
activities.
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Greenhouse Effect Venus, Earth, and Mars
VENUS (Same size as Earth)
EARTH
MARS (Half size of Earth)
Pressure 90 Atm. Atmosphere composed of
96 CO2 Temperature 482 C
Pressure 1 Atm. Atmosphere composed of
less than 1 CO2 Temperature 15 C
Pressure 0.01 Atm. Atmosphere composed of
95 CO2 Temperature -63 C
VIRTUALLY NO ATMOSPHERE TO HAVE A GREENHOUSE
EFFECT
GREENHOUSE EFFECT ON STERIODS!
GREENHOUSE EFFECT JUST RIGHT
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Weve talked so far about absorption and
emission of radiation in the atmosphere. This
process is most important for terrestrial
radiation.Reflection and scattering are more
important for solar radiation.
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Scattering Radiation deflected
Mie Scattering
Rayleigh Scattering
Atmospheric gases Molecules preferentially
scatter the smaller wavelengths of visible light.

Cloud drops Scatter all wavelengths of visible
light equally.
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Why is the sky blue?
Air molecules preferentially scatter smaller
wavelengths of visible light, which are blue!
36
Reflection Radiation turned back
In meteorology the reflectivity is called the
albedo. Albedo 1 ? All radiation
reflected Albedo 0 ? All radiation absorbed
Snow 0.7 Water 0.1 Vegetation 0.1 to
0.3 Sand 0.15 to 0.45 Clouds Depends on type
and location
NET ALBEDO OF EARTH 0.3
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Important AsideClouds are a big part of the
radiation budget too!
ABSORPTION AND REFLECTION OF SOLAR RADIATION
VERY EFFECTIVE ABSORBERS AND EMITTERS OF
TERRESTRIAL RADIATION
38
Now that we know what happens to radiation in the
atmosphere, were ready to look at the Earths
average energy budget
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Energy Budget Shortwave Radiation
INCOMING SOLAR AT TOA
EARTHS ALBEDO
ATMOSPHERIC ABSORPTION
SURFACE SOLAR ABSORPTION (ABOUT HALF OF TOTAL
INCOMING)
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Energy Budget Longwave radiation and Sensible
and Latent Heating
ATMOSPHERIC LONGWAVE EMISSION TO SPACE ( 1-
ALBEDO)
ATMOSPHERIC ENERGY GAINED FROM SURFACE
ATMOSPHERIC LONGWAVE EMISSION TO SURFACE
SURFACE LONGWAVE EMISSION
SENSIBLE AND LATENT HEATING
SURFACE LONGWAVE ABSORPTION GREENHOUSE EFFECT
SURFACE SOLAR ABSORPTION
SUM OF SHORTWAVE LONGWAVE ABSORPTION ( gt 100)
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Summary of Lecture 6
Radiation in the atmosphere has four possible
fates transmitted, reflected, scattered, or
absorbed. A perfect absorber and emitter of
radiation is called a blackbody. The
atmosphere selectively reflects, scatters and
absorbs radiation at certain wavelengths, which
depend on the specific gas constituents. Absorbed
radiation increases the internal energy by
changes on the molecular and atomic level.
Terrestrial radiation is associated with
translational, rotational, and vibrational energy
transitions on the molecular level. Solar
radiation is associated with electronic energy
transitions on the atomic level. Greenhouse
gases are those which absorb and emit very
effectively in the infrared, like water and CO2.
Because of them the atmosphere is very opaque to
terrestrial radiation and the Earths surface
temperature is maintained. Reviewed the
atmospheric energy budget to prove the
point. Though the atmosphere is fairly
transparent to solar radiation, scattering and
reflection of solar radiation is important.
Scattering of visible light is why the sky is
blue!
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Reading Assignment and Review Questions

• Ahrens, Chapter 3, pp. 55-63
• Chapter 2 Questions
• Questions for Review 11,12,13,14,17,18,19,21
• Questions for Thought 7,9,10,11,12,13