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Arctic Cloud Pollution Effects: Seasonal Variations in Cloud Properties and Surface Radiation Balance

Research by Tim Garrett from University of Utah explores associations between pollution and Arctic cloud effects on surface radiation balance. Collaborations with Chuanfeng Zhao, Kyle Tietze, and Melissa Maestas. Support from NSF and Clean Air Task Force. Findings indicate higher longwave cloud emissivity in winter and spring leading to a net surface warming of around 5 W/m2, with compensating surface cooling in summer for dark surfaces. Downwelling longwave fluxes increase in late winter and early spring, affecting cloud dynamics and radiative cooling at cloud tops. Interesting interactions between pollution and cloud properties, such as cloud cover, circulations, entrainment, and forcing, are suggested. Study used measurements, remote sensing data, and models.

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Arctic Cloud Pollution Effects: Seasonal Variations in Cloud Properties and Surface Radiation Balance

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  1. 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

  2. 600 m Arctic Stratus at full resolution (30 m x 300 m)

  3. Cloud Radiative Forcing

  4. Seasonality of Arctic Haze Winter/Spring Increase in Aerosol Nitrate and Sulfate Sources: Diesel and gasoline engines Coal fired power plants

  5. Summer - Aerosol Direct & Indirect Effects (-ΔT)

  6. Cloud Radiative Forcing Most Polluted

  7. Francis and Hunter, 2006

  8. Francis and Hunter, 2006

  9. Winter – Enhanced Cloud Longwave Emissivity (+ΔT) 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

  10. Cloud emissivity depends foremost on cloud thickness Garrett et al. (2002) JAS

  11. DJF MAM Blackbody <3.5 km

  12. JJA SON Blackbody <3.5 km

  13. Cloud emissivity also depends on re and potentially also Arctic pollution Garrett et al. (2002) JAS

  14. Measurements ARM remote sensing NOAA aerosol Barrow Site ERS-Gome satellite Ozone profile Temperature and water vapor profiles

  15. Looking up with FTIR at Barrow CO2 dirty window (looking up at outer space) Retrieval bands Strat. O3

  16. Upper haze quartile Clean Polluted Lower haze quartile All Low Cloud

  17. Liquid Cloud

  18. Ice Cloud

  19. Forcing normalized by monthly low cloud cover 10 W/m2 ~ 2.5 K Warming Cooling

  20. Liquid Cloud

  21. Climate Radiation Clouds Dynamics Microphysics

  22. Nominally clean Nominally polluted

  23. FLW FLW FLW

  24. Low clouds (z < 3km) High clouds (z > 7 km) Thick clouds (dz > 7 km) Kay et al. (in prep) A-train Arctic Clouds:Winter (DJF 06)

  25. 2006 2007 Kay et al. (in prep) Arctic low cloud anomaly in 2007

  26. Climate What is the direction of this arrow? Radiation Clouds Dynamics Microphysics

  27. 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

  28. Summary • Increases in downwelling longwave fluxes occur in late winter and early spring, at the beginning of the melting ‘push’

  29. 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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