Atmospheric Radiation GCC Summer School Montreal August 7, 2003

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Atmospheric RadiationGCC Summer SchoolMontreal
- August 7, 2003

• Glen Lesins
• Department of Physics and Atmospheric Science
• Dalhousie University
• Halifax
• glen.lesins_at_dal.ca

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Outline

• Introductory concepts
• Radiation and Climate
• Radiative Transfer Theory
• Remote Sensing

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Credits

• K.N. Liou, An Introduction to Atmospheric
  Radiation, 2nd Ed., 2002
• Web Lecture Notes by Prof. Irina Sokolik,
  http//irina.colorado.edu/teaching.htm

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Global Annual Energy Balance
Kiehl and Trenberth (1997) IPCC (2001)
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What is the Solar Constant?

• 1366 W m-2
• How constant?
• Earths orbit and tilt (annual)
• Sunspot cycle (11 years)
• Longer time variations

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Solar Irradiance Variation from ACRIM
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http//science.nasa.gov/headlines/images/sunbathin
g/sunspectrum.htm
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Solar vs. Terrestrial Radiation
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Absorption of Radiation by Gases
1. Ionization/Dissociation - UV 2. Electronic
Transition - UV 3. Vibrational/Rotational
Transition - Visible/IR 4. Pure Rotational - IR
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Transmission through the Atmosphere
Terrestrial
Solar
IR Window
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Radiative Interactions - Dipole Transitions
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Vibrational Modes
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Ozone (O3)

• Electrostatic potentialmap shows both
  endoxygens are equivalentwith respect to
  negativecharge. Middle atomis positive.

www.facstaff.oglethorpe.edu/mwolf/PowerPoint/
CareyOrgPP/sections1st/Chapter201bx.ppt
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Absorption by Gases
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Solar Irradiance
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Scattering of Radiation
Size Parameter, a a 2pr/l
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Rayleigh Scattering
http//hyperphysics.phy-astr.gsu.edu/hbase/atmos/b
lusky.htmlc2
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Mie Theory for mr1.5
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Normalized Phase Functions From Mie Theory
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Global Annual Energy Balance
Kiehl and Trenberth (1997) IPCC (2001)
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Zonal Average Irradiance
Solar
Terrestrial
Net
Meridional Transport
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Cloud Radiative Forcing from ERBE
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Radiative Equilibrium Role of Convection
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Solar Heating Rates from Model
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Zonal Annual Average from Satellite
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Results from SOCRATES (2-D Radiative-Chemical)
http//acd.ucar.edu/models/SOCRATES/socrates/socra
tes1.html
http//acd.ucar.edu/models/SOCRATES/socrates/socra
tes1.html
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Annual Mean Net Radiation Flux from Surface Based
Measurements
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Terrestrial IR Spectra
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Modelled IR Fluxes
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Global Annual Energy Balance
Kiehl and Trenberth (1997) IPCC (2001)
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Radiative Transfer Equation
Radiance
Cosine of solar zenith angle
Azimuthal Angle
Beers Law
Source Function
Optical Depth
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Plane Parallel Radiances
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Solution to the Radiative Transfer Equation
Upward Radiance
Downward Radiance
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Single Multiple Scattering Source
Source Function
Multiple Scattering Term
Single Scattering Term
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Surface Reflectance
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Bi-directional Reflectance Distribution Function
(BRDF)
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Surface Albedo
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Remote Sensing of Clouds
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Effect of Clouds from Radiative-Convective Model
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Solar Albedo of Clouds - Theory
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Indirect Aerosol Effect - ShiptracksL1B true
color RGB composite (25 April 2001)
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Effective radius retrieval (using 2.1 µm band,
all phases)
60
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re (µm)
30
15
0
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Shiptracks from MODIS Indirect Aerosol Effect
July 1, 2003
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Global Annual Energy Balance
Kiehl and Trenberth (1997) IPCC (2001)
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IR Brightness Temperature from ER-2 (Clear)
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Brightness Temperatures From ER-2 (Various Clouds)
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Polarization of Sunlight Reflected by Venus
PointsObs LinesTheory
Hansen and Hovenier, 1974
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POLDER Polarization for Ice Habits
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Ice Crystal Phase Functions
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Cloud Fraction from Satellites
http//isccp.giss.nasa.gov
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TERRA - Launched Dec. 18, 1999(MODIS, ASTER,
MISR, CERES, MOPITT)

• MODIS
• 1-2 day global coverage in 36 wavelengths from
  250 m to 1 km resolution
• MISR
• Stereo images at 9 look angles
• ASTER
• Hi-resolution, multi-spectral images from 15 m to
  90 m resolution, plus stereo
• MOPITT
• Global measures of CH4 CO
• CERES
• Measures Earths shortwave, longwave,
• net radiant energy budget

http//modis-atmos.gsfc.nasa.gov/reference.html
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MODIS Atmospheric Products

• Pixel-level (level-2) products
• Cloud mask for distinguishing clear sky from
  clouds
• Cloud radiative and microphysical properties
• Cloud top pressure, temperature, and effective
  emissivity
• Cloud optical thickness, thermodynamic phase, and
  effective radius
• Thin cirrus reflectance in the visible
• Aerosol optical properties
• Optical thickness over the land and ocean
• Size distribution (parameters) over the ocean
• Atmospheric moisture and temperature gradients
• Column water vapor amount
• Gridded time-averaged (level-3) atmosphere
  product
• Daily, 8-day, and monthly products
• 1 x 1 equal angle grid
• Mean, standard deviation, marginal probability
  density function, joint probability density
  functions
• modis-atmos.gsfc.nasa.gov

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MODIS - TERRA True colour image Dust over
the Mediterranian March 12, 2003
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CO2 Slicing Method

• CO2 slicing method
• ratio of cloud forcing at two near-by wavelengths
• assumes the emissivity at each wavelength is
  same, and cancels out in ratio of two bands
• The more absorbing the band, the more sensitive
  it is to high clouds
• technique the most accurate for high and middle
  clouds
• MODIS is the first sensor to have CO2 slicing
  bands at high spatial resolution (1 km)
• technique has been applied to HIRS data for 20
  years
• retrieved for every 5 x 5 box of 1 km FOVs, when
  at least 5 FOVs are cloudy, day night

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Brightness Temperature in 15 mm CO2 band
Arrows at Wavelengths Measured by VTPR
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Retrieval of Cloud Optical Depth and Effective
Radius

• The reflection function of a nonabsorbing band
  (e.g., 0.86 µm) is primarily a function of
  optical thickness
• The reflection function of a near-infrared
  absorbing band (e.g., 2.14 µm) is primarily a
  function of effective radius
• clouds with small drops (or ice crystals) reflect
  more than those with large particles
• For optically thick clouds, there is a near
  orthogonality in the retrieval of tc and re using
  a visible and near-infrared band

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Cloud Optical DepthApril 2001
20
10
0
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Cloud Effective Particle RadiusApril 2001
40
22
4 mm
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Remote Sensing of Aerosols
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Global Annual Energy Balance
Kiehl and Trenberth (1997) IPCC (2001)
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Global Aerosol Emissions (Tg / yr)
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Annual Global Volcanic Aerosol Loading
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Aerosol Optical Weighting Functions
Kl(a)pa2Qen(a)Qe/reff
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Model Aerosol Type Optical Thickness
http//www.giss.nasa/gov/data
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MODIS Aerosol Optical Properties

• Seven MODIS bands are utilized to derive aerosol
  properties
• 0.47, 0.55, 0.65, 0.86, 1.24, 1.64, and 2.13 µm
• Ocean
• reflectance contrast between cloud-free
  atmosphere and ocean reflectance (dark)
• aerosol optical thickness (0.55-2.13 µm)
• size distribution characteristics (fraction of
  aerosol optical thickness in the fine particle
  mode effective radius)
• Land
• dense dark vegetation and semi-arid regions
  determined where aerosol is most transparent
  (2.13 µm)
• contrast between Earth-atmosphere reflectance and
  that for dense dark vegetation surface (0.47 and
  0.66 µm)
• enhanced reflectance and reduced contrast over
  bright surfaces (post-launch)
• aerosol optical thickness (0.47 and 0.66 µm)

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Gobi Desert Dust Storm - March 20, 2001 MODIS
ta (0.55 µm)
2.0
1.0
0
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Aerosol Optical Thickness - MODISFine Particle
Mode
ta (0.55 µm)
0.8
0.4
0
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TOMS - Aerosol Index - Feb 26, 2000
http//toms.gsfc.nasa.gov/index.html
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LITE - Lidar In space Technology
Experiment September 1994 - Space Shuttle
Deep Convection
Saharan Dust
http//www-lite.larc.nasa.gov/
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Remote Sensing of Gases
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Radiative Forcing Between 1850 to 2000
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Global Annual Energy Balance
Kiehl and Trenberth (1997) IPCC (2001)
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Atmospheric Transmittances in the Microwave
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Microwave Emissivity of Ocean Surface
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Microwave Brightness Temperature
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Precipitable Water
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Source/Aerosol 355nm N2
387nm Water Vapour 408nm
http//www.arm.gov/docs/instruments/static/rl.html
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Raman Lidar to Measure Water Vapour Profile
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GPS Signals to Measure Water Vapour
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http//atmos.af.op.dlr.de/projects/scops/
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Normalised weighting functions for the High
Resolution Infrared Sounder (HIRS) on NOAA
satellites. Each function indicates the relative
contribution of the atmosphere from a given level
to the radiance observed at the satellite through
the numbered channel.
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Satellite Limb Scanning
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Limb Scanning Weighting Functions
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Global Annual Energy Balance
Kiehl and Trenberth (1997) IPCC (2001)
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Final Comments

• Ultimately radiation drives all processes in the
  atmosphere
• Remote sensing will continue to grow as a source
  of atmospheric measurements
• New suite of satellites will require more
  atmospheric scientists in this area

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Solar Ultra-violet Spectrum
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Optical Properties for Typical Stratus and Cumulus
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Bidirectional Reflectance and Absorbance of
Cirrus Clouds
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LIDARS
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Brightness Temperature in 15 mm CO2 band
Arrows at Wavelengths Measured by VTPR
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IR Brightness Temperature from ER-2
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