Associations between pollution and the effects of clouds on the Arctic LW and SW surface radiation balance

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Associations between pollution and theeffects of
clouds on the Arctic LW and SW surface radiation
balance

• Tim Garrett
• University of Utah
• Collaborations with Chuanfeng Zhao, Kyle Tietze
  and Melissa Maestas at UU
• Support from NSF and Clean Air Task Force

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Arctic Stratus at full resolution (30 m x 300 m)
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Cloud Radiative Forcing
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Seasonality of Arctic Haze Winter/Spring
Increase in Aerosol Nitrate and Sulfate
Sources Diesel and gasoline engines

Coal fired power plants
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Summer - Aerosol Direct Indirect Effects (-?T)
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Cloud Radiative Forcing
Most Polluted
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Francis and Hunter, 2006
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Francis and Hunter, 2006
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Winter Enhanced Cloud Longwave Emissivity (?T)
Thin, polluted cloud. Better insulator. Heat
is trapped and re-emitted. Garrett and Zhao,
Nature, 2006
Thin, clean cloud Poor insulator Heat escapes
F(LW) ??T4
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Cloud emissivity depends foremost on cloud
thickness
Garrett et al. (2002) JAS
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DJF
MAM
Blackbody
lt3.5 km
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JJA
SON
Blackbody
lt3.5 km
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Cloud emissivity also depends on re and
potentially also Arctic pollution
Garrett et al. (2002) JAS
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Measurements
ARM remote sensing
NOAA aerosol
Barrow Site
ERS-Gome satellite Ozone profile
Temperature and water vapor profiles
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Looking up with FTIR at Barrow
CO2
dirty window
(looking up at outer space)
Retrieval bands
Strat. O3
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Upper haze quartile
Clean
Polluted
Lower haze quartile
All Low Cloud
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Liquid Cloud
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Ice Cloud
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Forcing normalized by monthly low cloud cover
10 W/m2 2.5 K
Warming
Cooling
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Liquid Cloud
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Climate
Radiation
Clouds
Dynamics
Microphysics
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Nominally clean
Nominally polluted
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FLW
FLW
FLW
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A-train Arctic CloudsWinter (DJF 06)
Kay et al. (in prep)
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Arctic low cloud anomaly in 2007
2006
2007
Kay et al. (in prep)
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Climate
What is the direction of this arrow?
Radiation
Clouds
Dynamics
Microphysics
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Summary

• Seasonal pollution is associated with changes in
  low-level Arctic cloud properties
• Higher longwave cloud emissivity
• Net surface warming in winter and spring (about 5
  W/m2)
• Compensating surface cooling in summer if surface
  is dark

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Summary

• Increases in downwelling longwave fluxes occur in
  late winter and early spring, at the beginning of
  the melting push

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Summary

• The CRF increases are larger than would be
  expected from effective radius decreases alone
• There may be interesting interactions between
  pollution and cloud dynamics, associated with
  enhanced cloud top radiative cooling
• Cloud cover
• Cloud circulations
• Cloud top entrainment
• Cloud forcing?

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