1. Atmospheric Radiation GCC Summer School Montreal - August 7, 2003
Glen Lesins
Department of Physics and Atmospheric Science
Dalhousie University
Halifax

2. Outline Introductory concepts Radiation and Climate
Radiative Transfer Theory
Remote Sensing

3. Credits
K.N. Liou, An Introduction to Atmospheric Radiation, 2nd Ed., 2002
Web Lecture Notes by Prof. Irina Sokolik,

4. Global Annual Energy Balance
Kiehl and Trenberth (1997); IPCC (2001)

6. What is the Solar Constant?
1366 W m-2
How constant?
Earth’s orbit and tilt (annual)
Sunspot cycle (11 years)
Longer time variations

7. Solar Irradiance Variation from ACRIM

9. Solar vs. Terrestrial Radiation

10. Absorption of Radiation by Gases
1. Ionization/Dissociation - UV
2. Electronic Transition - UV
3. Vibrational/Rotational Transition -
Visible/IR
4. Pure Rotational - IR

11. Transmission through the Atmosphere
Solar
Terrestrial
IR Window

12. Radiative Interactions - Dipole Transitions

13. Vibrational Modes

14. Ozone (O3)
Electrostatic potential map shows both end oxygens are equivalent with respect to negative charge. Middle atom is positive. O ••
• • – + O ••
• • – +
CareyOrgPP/sections1st/Chapter%201bx.ppt 26

15. Absorption by Gases

17. Solar
Irradiance

18. Scattering of Radiation
Particle
Size
Wavelength
Size Parameter, a
a = 2pr/l

19. Rayleigh Scattering

20. Mie Theory for mr=1.5

21. Normalized
Phase
Functions
From
Mie Theory

22. Global Annual Energy Balance
Kiehl and Trenberth (1997); IPCC (2001)

23. Zonal Average Irradiance
Solar
Terrestrial
Net
Meridional
Transport

24. Cloud Radiative Forcing from ERBE

25. Radiative Equilibrium & Role of Convection

26. Solar Heating Rates from Model

27. Zonal Annual Average from Satellite

28. Results from SOCRATES (2-D Radiative-Chemical)

29. Annual Mean Net Radiation Flux from Surface
Based Measurements

30. Terrestrial IR Spectra

31. Modelled IR Fluxes

34. Radiative forcing (W m-2)
High
Level of Scientific Understanding 1 2 3 -1 -2
Medium
Low
Very
Halocarbons N O CH 4 CO
Aerosols
Aviation-induced
Tropospheric
ozone
Stratospheric
Black
carbon from
fossil fuel
burning
Organic
carbon
from
fossil
fuel
Aerosol
indirect
effect
Biomass
Land-use
(albedo)
only
Mineral
dust
Sulphate
Contrails
Cirrus
Solar
Global mean radiative forcing of the climate
system for the year 2000, relative to 1750
Radiative forcing (W m-2)
Warming
Cooling

35. Global Annual Energy Balance
Kiehl and Trenberth (1997); IPCC (2001)

36. Radiative Transfer Equation
Radiance
Cosine of solar
zenith angle
Azimuthal Angle
Beer’s Law
Source Function
Optical Depth

37. Plane Parallel Radiances

38. Solution to the Radiative Transfer Equation
Upward
Radiance
Downward
Radiance

39. Single & Multiple Scattering Source
SUN
Source Function
Multiple Scattering Term
Single Scattering Term

40. Surface Reflectance

41. Bi-directional Reflectance
Distribution Function (BRDF)

42. Surface Albedo

43. Remote Sensing of Clouds

44. Effect of Clouds from Radiative-Convective
Model

45. Solar Albedo of Clouds - Theory

46. Indirect Aerosol Effect - Shiptracks L1B true color RGB composite (25 April 2001)

47. Effective radius retrieval (using 2.1 µm band, all phases)60 45 30
re (µm) 15

48. Indirect Aerosol Effect
Shiptracks from MODIS
Indirect Aerosol Effect
July 1, 2003

49. Global Annual Energy Balance
Kiehl and Trenberth (1997); IPCC (2001)

50. IR Brightness Temperature from ER-2 (Clear)

51. Brightness
Temperatures
From ER-2
(Various Clouds)

52. Polarization of Sunlight Reflected by Venus
Points=Obs
Lines=Theory
Hansen and Hovenier, 1974

53. POLDER – Polarization for Ice Habits

54. Ice Crystal Phase Functions

55. Cloud Fraction from Satellites

56. TERRA - Launched Dec. 18, 1999 (MODIS, ASTER, MISR, CERES, MOPITT)
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 Earth’s shortwave, longwave,
net radiant energy budget

57. 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

59. MODIS - TERRA
True colour image
Dust over the
Mediterranian
March 12, 2003

60. 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

61. Brightness Temperature in 15 mm CO2 band
Arrows at
Wavelengths
Measured by
VTPR

62. 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

63. Cloud Optical Depth April 200110

64. Cloud Effective Particle Radius April 200140 22
4 mm

66. Remote Sensing of Aerosols

67. Global Annual Energy Balance
Kiehl and Trenberth (1997); IPCC (2001)

68. Global Aerosol
Emissions
(Tg / yr)

69. Annual Global Volcanic Aerosol Loading

70. Aerosol Optical Weighting Functions
Kl(a)=pa2Qen(a)~Qe/reff

71. Model Aerosol Type Optical Thickness

72. 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 ( 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)

73. Gobi Desert Dust Storm - March 20, 2001 MODIS
ta (0.55 µm)
2.0
1.0

74. Aerosol Optical Thickness - MODIS Fine Particle Mode
ta (0.55 µm)
0.8
0.4

75. TOMS - Aerosol Index - Feb 26, 2000

76. LITE - Lidar In space Technology Experiment
September Space Shuttle
Deep Convection
Saharan Dust

78. Remote Sensing of Gases

79. Radiative Forcing Between 1850 to 2000

80. Global Annual Energy Balance
Kiehl and Trenberth (1997); IPCC (2001)

81. Atmospheric Transmittances in the Microwave

82. Microwave Emissivity of Ocean Surface

83. Microwave Brightness Temperature

87. Precipitable Water

88. Source/Aerosol 355nm N2 387nm Water Vapour 408nm

89. Raman Lidar to Measure Water Vapour Profile

91. GPS Signals to Measure Water Vapour

94. 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.

95. Satellite Limb Scanning

96. Limb Scanning
Weighting
Functions

97. Global Annual Energy Balance
Kiehl and Trenberth (1997); IPCC (2001)

98. 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

101. Solar Ultra-violet Spectrum

102. Optical Properties for Typical Stratus and Cumulus

103. Bidirectional Reflectance and Absorbance
of Cirrus Clouds

105. LIDARS

107. Brightness Temperature in 15 mm CO2 band
Arrows at
Wavelengths
Measured by
VTPR

108. IR Brightness Temperature from ER-2