Aerosol-cloud-radiation feedbacks in the Arctic

 

Support by NSF and the Clean Air Task Force


The climate of the Arctic is changing rapidly. Ever since the 1800s, there have been observations commenting on a seasonal cycle in Arctic aerosol pollution. Pollution is high in winter and low in summer. The past decades have shown that much of these aerosol are due to human activities at mid-latitudes, and there is increasing concern that they might also contribute to Arctic surface warming.


With former students Kyle Tietze, Sara Brattstrom and Chuanfeng Zhao, our work is showing the role that clouds play in controlling this seasonal cycle, and how pollution is changing cloud properties in such a way that might add to Arctic surface warming. We are finding that the properties of arctic stratus clouds are unusually sensitive to pollution and biomass burning aerosols exported to the Arctic from mid-latitudes.  Cloud droplet sizes become smaller, clouds become thicker, and they become more efficient emitters of thermal radiation, which potentially warms the arctic surface in winter and early spring. 


For a very nice summary on our studies produced by International Innovation (see byline below), please see Aerosol Assault on the Arctic.


Garrett, T. J., S. Brattström*, S. Sharma, D. E. J. Worthy, and P. Novelli, 2011: The role of scavenging in the seasonal transport of black carbon and sulfate to the Arctic, Geophys. Res. Lett., 38, L16805, doi:10.1029/2011GL048221.


Tietze, K.*, Riedi, J., Stohl, A. and Garrett, T. J. Space-based evaluation of interactions between aerosols and low-level Arctic clouds during the Spring and Summer of 2008 Atmos. Chem. Phys., 11, 3359-3373, doi:10.5194/acp-11-3359-2011 , 2011


Garrett, T. J.*, C. Zhao*, and P. Novelli, 2010: Assessing the relative contributions of transport efficiency and scavenging to seasonal variability in Arctic aerosol. Tellus B, 62, 190 - 196


Garrett, T. J., M. M. Maestas*, S. K. Krueger, and C. T. Schmidt, 2009, Acceleration by aerosol of a radiative-thermodynamic cloud feedback influencing Arctic surface warming, Geophys. Res. Lett., 36, L19804, doi:10.1029/2009GL040195.


Zhao, C.*, and T. J. Garrett, 2008: Ground-based remote sensing of precipitation in the Arctic, J. Geophys. Res., 113, D14204, doi:10.1029/2007JD009222


Garrett, T. J. and C. Zhao*, 2006: Increased Arctic cloud longwave emissivity associated with pollution from mid-latitudes. Nature, 440, 10.1038/nature04636, 787-789


Garrett, T. J., C. Zhao*, X. Dong, G. G. Mace, P. V. Hobbs, 2004: Effects of Varying Aerosol Regimes on Low-Level Arctic Stratus. Geophys. Res. Lett. Vol. 31, No. 17, L17105 10.1029/2004GL019928 PDF


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