Climatology Lecture 2

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ClimatologyLecture 2

• Michael Palmer
• Radiation and Climate
• email mpalmer_at_atm.ox.ac.uk
• Lectures available on www.atm.ox.ac.uk/user/mpalm
  er/

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6000K
short wave
visible
99.99 energy
288 K long wave infrared
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Radiation Laws

• Wilhelm Wien
• Josef Stefan
• Ludwig Boltzmann
• Max Planck

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Lecture Outline

• Attenuation of radiation
• Longwave radiation and ...
• The Greenhouse Effect
• Radiation Budget

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Attenuation of Shortwave Radiation

• Reflection
• Scattering
• Absorption

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Reflection

• Change in direction of the solar beam
• albedo (fraction of incident radiation reflected
  by the surface)
• fresh snow 75-95
• cumuliform cloud 70-90
• grassland 15-25
• forest 10-20

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Absorption

• Radiation is transformed into heat by absorption
  of certain gases at specific wavelengths
• strong absorption occurs at some wavelengths,
  very little at others

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Absorption

• Almost all ultra-violet radiation ( lt 0.29
  microns) absorbed by oxygen and ozone
• little absorption occurs between 0.3 and 0.8
  microns
• atmosphere is transparent to the major part of
  the solar spectrum

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Scattering

• Change in direction of the solar beam, but occurs
  selectively
• dependent on size of scattering particle and
  wavelength of radiant energy
• Blue light scattered preferentially
• short wavelengths more efficiently scattered than
  long wavelengths - occurs when scattering bodies
  are much smaller than the incident wavelengths
  (blue light scattering is 6 times more efficient
  than red light)
• Rayleigh scatteringMie scattering

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Net Shortwave flux at the top of the atmosphere

• Net shortwave incoming shortwave - shortwave
  reflected to space

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Lecture Outline

• Attenuation of radiation
• Longwave radiation and ...
• The Greenhouse Effect
• Radiation Budget

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Shortwave Radiation
Layer 3
Layer 2
Layer 1
Surface
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Shortwave Radiation
Layer 3
Layer 2
Layer 1
Surface
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Shortwave Radiation
Layer 3
Layer 2
Layer 1
Surface
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Shortwave Radiation
Layer 3
Layer 2
Layer 1
Surface
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Shortwave Radiation
Layer 3
Layer 2
Layer 1
Surface
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Shortwave Radiation
Lost to Space
Layer 3
Layer 2
Layer 1
Surface
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Shortwave Radiation
Lost to Space
Layer 3
Layer 2
Layer 1
Surface
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Terrestrial Radiation lost to space

• 90 of the terrestrial radiation emitted to
  space comes from the atmosphere
• 10 comes through the window from the underlying
  land and sea

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Terrestrial Radiation absorbed in the Atmosphere

• Water vapour 2.5 to 3.5 microns
  5 to 7 microns
  gt 13 microns
• Carbon dioxide 1.6 microns
  2.0 microns
  2.7 microns 4.3 microns
  15 micronsAtmospheric window 10
  microns

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Natural Greenhouse Effect

• Water vapour and carbon dioxide
• Water vapour feedback
• carbon dioxide increases

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Effective Temperature

• Radiation In Radiation Out
• Solar Radiation Terrestrial Radiation

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Effective Temperature

• Radiation In Radiation Out
• Solar Radiation Terrestrial Radiation
• Solar constant (S) emission based on
• albedo losses (A) Earths temperature
• area of the earth Stefan-Boltzmann
  Equation

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Effective Temperature

• Radiation In Radiation Out
• Solar Radiation Terrestrial RadiationSolar
  constant X area S-Bolt law applied
  circle to area of spherepi.r2.S. pi.r2.S.A
  area of sphere X cT4 pi.r2.S.(1-A)
  4 pi r2 cT4

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Effective Temperature

• Radiation In Radiation Outsolve for T
  from pi r2 S(1-A) 4 pi r2 cT4(pi r2
  S(1-A)) T44 pi r2c

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Effective Temperature

• Radiation In Radiation OutSolve for T
  from(pi r2 S(1-A)) T44 pi r2cS(1-0.3)
  T44c1370(1-0.3) T44(5.67 x 10-8)

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Effective Temperature

• Radiation In Radiation OutSolve for T
  from250 K T

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Radiation Budget

• Shortwave Radiation In
• Shortwave and Longwave Radiation Out
• Shortwave Radiation Out (reflected)
• Longwave Radiation Out (emitted)
• Radiation Budget
• (Sin Lin) - (Sout Lout)

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WWW Sites for looking at global maps of climate
variables

• http//www.cdc.noaa.gov/Composites/
• http//www.cdc.noaa.gov/PublicData/web_tools.html

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Readings for todays Lecture

• Barry, R.G. and Chorley, R.J. 1998 Atmosphere,
  Weather and Climate (7th Ed.) Chapter 2 (H679)
• Eagleman, J.R. 1980 Meteorology, the atmosphere
  in action Chapter 3.
• Henderson-Sellers, A. and Robinson, P.J. 1999
  Contemporary Climatology. Harlow Chapter 2 (H693)
• Lockwood, J.G. 1974 World Climatology. An
  Environmental Approach. London Edward Arnold,
  330pp. page 6-14.
• McIlven, J.F.R. 1992 Fundamental of Weather and
  Climate. Wokingham Van Norstrand Reinhold,
  457pp. Chapter 8.
• OHare, G. and Sweeney, J.1987 The atmospheric
  system (SoG H450)
• Briggs, D. et al 1997. Fundamentals of Physical
  Environment, Chapters 2-4.