CH 8: ATMOSPHERIC EMISSION: PRACTICAL CONSEQUENCES OF THE SCHWARZSCHILD EQUATION FOR RADIATION TRANSFER WHEN SCATTERING IS NEGLIGIBLE

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CH 8 ATMOSPHERIC EMISSION PRACTICAL
CONSEQUENCES OF THE SCHWARZSCHILD EQUATION FOR
RADIATION TRANSFER WHEN SCATTERING IS NEGLIGIBLE

• Key Concepts
• Infrared transmission and emission by the
  atmosphere gases.
• Learn how to read meteorology in infrared
  spectra.
• Learn about the basic concepts involved with
  retrieval of atmospheric temperature and humidity
  - weighting functions.

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Some Energy States of Water Molecules
http//www.lsbu.ac.uk/water/vibrat.html
http//en.wikipedia.org/wiki/Libration
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Atmospheric Transmission Beers Law
I(x)I0e(-?abs x)
What are the main sources for each gas? Which
gases are infrared active and contribute to
greenhouse warming? Which gases significantly
absorb solar radiation?
Gas concentrations from typical midlatitude
summer atmosphere.
Nitrous oxide is emitted by bacteria in soils and
oceans, and thus has been a part of Earth's
atmosphere for eons. Agriculture is the main
source of human-produced nitrous oxide
cultivating soil, the use of nitrogen
fertilizers, and animal waste handling can all
stimulate naturally occurring bacteria to produce
more nitrous oxide. The livestock sector
(primarily cows, chickens, and pigs) produces 65
of human-related nitrous oxide. 1 Industrial
sources make up only about 20 of all
anthropogenic sources, and include the production
of nylon and nitric acid, and the burning of
fossil fuel in internal combustion engines. Human
activity is thought to account for somewhat less
than 2 teragrams of nitrogen oxides per year,
nature for over 15 teragrams.
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Clouds at Visible and IR (e.g. 10 um) Wavelengths
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Optics of N identical (particles / volume)
Light beam area A
z
dz
zdz
Power removed in dz I(z) N A dz ?ext
Bouger-Beer law (direct beam only!)
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CH 8 ATMOSPHERIC EMISSION PRACTICAL
CONSEQUENCES OF THE SCHWARZSCHILD EQUATION FOR
RADIATION TRANSFER WHEN SCATTERING IS NEGLIGIBLE
What process subtracts radiation? What process
adds radiation?
What equation is used to calculate optical depth
for a gaseous atmosphere?
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FTIR Radiance Atmospheric IR Window
13 microns
8 microns
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DEFINITION OF THE BRIGHTNESS TEMPERATURETB
Measured Radiance at wavenumber v
Theoretical Radiance of a Black
Body at temperature TB
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FTIR Brightness Temperatures
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Atmosphere Emission Measurements, Downwelling
Radiance

• Notes
• Wavelength range for CO2, H20, O3, CH4.
• Envelope blackbody curves.
• Monster inversion in Barrow.
• Water vapor makes the tropical window dirty.

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Ideal Weighting Function Wi Where in the
atmosphere the main contribution to the radiation
at wavenumber ?i comes from.
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Downwelling Intensity Emitted by the Atmosphere
to the Detector (Radiance)
?cos?
BT(z)
emissivity?absdz/cos?
z
dz
q
blackbody radiance, T temperature.
q
ftir
transmission
emission
weighting function
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Weighting Functions for Satellite Remote Sensing
using the strong CO2 absorption near 15.4 um.
(from Wallace and Hobbs, 2nd edition)
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Chapter 8 Homework

1. Calculate and plot weighting functions as in the
   previous slide, but for the FTIR spectrometer at
   the ground looking up.(500 to 850 cm-1 region).
2. Explain in detail, using these weighting
   function, how we can diagnose the temperature
   inversion in the Barrow Alaska graph.
3. Bring questions to class related to how this is
   done.
4. Extra credit Calculate and plot weighting
   functions for the stratospheric ozone emission
   spectral region in the atmospheric window region
   (spectral region between 1000 and 1100 cm-1.)

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Simple Theory for W(z) at the Ground
Where is the HUGE approximation? Why?
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Simple Theory for W(z) at the Ground
Where is the HUGE approximation? Why?
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http//www.spectralcalc.com/calc/spectralcalc.php
volume mixing ratio 0.01 (CO2) 0.1 (others)
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http//www.spectralcalc.com/calc/spectralcalc.php
Can save text file!
volume mixing ratio 0.01 (CO2)
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Calculate the absorption cross section per
molecule from the transmittance calculations and
this theory.
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CO2 Spectrum Line Strength and Broadening Effects
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CO2 Spectrum Line Strength and Broadening Effects
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?abs0, P1013.25 mb, T296 K. ONLY CO2!!! ??0.5
cm-1.
380 ppm CO2
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http//www.spectralcalc.com/atmosphere_browser/atm
osphere.php
Calculate N(z), then NH20(z), Nco2(z),
etc. Calculate ?abs(z) depth. Calculate W(z)
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RENO FTIR SPECTRA
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Weighting Functions for the FTIR at the Ground
Looking Up
H6 km
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Weighting Functions for the FTIR at the Satellite
Looking Down
H6 km
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Theoretical Absorption Cross Sections for the
indicated gases, averaged to 1 cm-1 resolution
for clarity.
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Theoretical Absorption Cross Sections for the
indicated gases, averaged to 1 cm-1 resolution
for clarity.
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RENO FTIR SPECTRA
Which day is more moist?
Which day is warmer near the surface?
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Coincident FTIR Measurements, Down and Up.
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More Examples of FTIR Data from a Satellite
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Comments on Figure 8.3.
The very strong CO2 line at 15 microns typically
gives the gas temperature closest to the FTIR
spectrometer.
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Self Study Questions
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FTIR Data from the NASA ER2 with Responsible
Gases labeled.
IR Window 8-13 microns. IR radiation from the
Earths surface escapes to space (cooling the
Earth). Absorption by O3 near 9 microns dirties
the window. (From Liou, pg 120).
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Atmospheric Temperature Profile US Standard
Atmosphere.
Cirrus cloud level. High cold clouds, visible
optical depth range 0.001 to 10, emits IR to
surface in the IR window.
From Liou
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Cirrus Clouds Small Crystals at Top, -40 C to
-60 C
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FTIR Data from the NASA ER2, Clear and Cloudy
Sky. (From Lious book). The ice cloud with
small ice crystals has emissivity ltlt 1, so the
ground below is partially seen. Clouds reduce
the IR making it to space in the atmospheric
window region.
IR Atmospheric window region
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Ice Refractive Index
Red shows the atmospheric window region. The
resonance in the window region is useful for
remote sensing. The real part goes close to 1,
making anomalous diffraction theory a fairly
reasonable approach for cross sections.
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Skin Depth and Absorption Efficiency
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Cloud Emissivity in General and Zero Scattering
Approximation.
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Cirrus with Small Crystals IR Transmission Model
Message Curve has basic shape of the IR
spectrum for small cirrus, primarily a
transmission problem of ground radiance through
the cloud, with a small emission correction.
ASSUMES ZERO SCATTERING.
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Cirrus with Small Crystals IR Emission Model
Message Curve has basic shape of the IR
spectrum for small cirrus, primarily a
transmission problem of ground radiance through
the cloud, with a small emission correction.
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Cirrus with Small Crystals IR Emission Model
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IR Cooling Rates(from Liou)
Message Clouds are good absorbers and emitters
of IR radiation. MLS is a moist midlatitude
profile, SAW is a dry subarctic winter
profile. Cooling rate is from the vertical
divergence of the net irradiance absorbed and
emitted.