Tim Garrett University of Utah
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Transcript of Tim Garrett University of Utah
Associations between pollution and the
effects of clouds on the Arctic LW and SW surface
radiation balanceTim Garrett
University of UtahCollaborations with Chuanfeng Zhao, Kyle
Tietze and Melissa Maestas at UU
Support from NSF and Clean Air Task Force
Arctic Stratus at full resolution (30 m x 300 m)
600 m
Cloud Radiative Forcing
Seasonality of Arctic Haze Winter/Spring Increase in Aerosol Nitrate and Sulfate
Sources: Diesel and gasoline engines
Coal fired power plants
0.06
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1/82 1/84 1/86 1/88 1/90 1/92 1/94 1/96 1/98 1/00 1/02 1/04
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1/98 1/99 1/00 1/01 1/02 1/03 1/04
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Alert
Barrow
NO3-, ug N m-3
SO4=, ug S m-3
Summer - Aerosol Direct & Indirect Effects (-ΔT)
Cloud Radiative Forcing
Most Polluted
Francis and Hunter, 2006
Francis and Hunter, 2006
Winter – Enhanced Cloud Longwave Emissivity (+ΔT)
Thin, clean cloudPoor insulatorHeat escapes
Thin, polluted cloud.Better insulator. Heat istrapped and re-emitted. [Garrett and Zhao, Nature, 2006]
F(LW) = T4
Cloud emissivity depends foremost on cloud thickness
Garrett et al. (2002) JAS
DJF MAM
Blackbody
<3.5 km
JJA SON
Blackbody
<3.5 km
Cloud emissivity also depends on re and potentially also Arctic pollution
Garrett et al. (2002) JAS
Measurements
ARM
remote
sensing
Barrow Site
ERS-Gome satellite Ozone profile
NOAA
aerosol
Temperature and water vapor profiles
CO2
Strat. O3
dirty window
Looking up with FTIR at Barrow
(looking up at outer space)
Retrieval bands
Upper hazequartile
Lower haze quartile
All LowCloud
CleanPolluted
Liquid Cloud
Ice Cloud
Forcing normalized by monthly low cloud cover
Warming
Cooling
10 W/m2 ~ 2.5 K
Liquid Cloud
Microphysics
Radiation
Dynamics
Climate
Clouds
Nominally clean Nominally polluted
€
€
€
FLW FLW FLW
A-train Arctic Clouds:Winter (DJF 06)
Low clouds(z < 3km)
High clouds(z > 7 km)
Thick clouds (dz > 7 km)
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Kay et al. (in prep)
Arctic low cloud anomaly in 2007
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2006 2007Kay et al. (in prep)
Microphysics
Radiation
Dynamics
Climate
Clouds
What is the direction of this arrow?
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
Summary
• Increases in downwelling longwave fluxes occur in late winter and early spring, at the beginning of the melting ‘push’
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?