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Volume 16, issue 7 | Copyright
Atmos. Chem. Phys., 16, 4661-4674, 2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 14 Apr 2016

Research article | 14 Apr 2016

Effects of long-range aerosol transport on the microphysical properties of low-level liquid clouds in the Arctic

Quentin Coopman1,2, Timothy J. Garrett1, Jérôme Riedi2, Sabine Eckhardt3, and Andreas Stohl3 Quentin Coopman et al.
  • 1Department of Atmospheric Sciences, University of Utah, Salt Lake City, UT, USA
  • 2Laboratoire d'Optique Atmosphérique, Université de Lille/CNRS, Lille, France
  • 3Norwegian Institute for Air Research, Kjeller, Norway

Abstract. The properties of low-level liquid clouds in the Arctic can be altered by long-range pollution transport to the region. Satellite, tracer transport model, and meteorological data sets are used here to determine a net aerosol–cloud interaction (ACInet) parameter that expresses the ratio of relative changes in cloud microphysical properties to relative variations in pollution concentrations while accounting for dry or wet scavenging of aerosols en route to the Arctic. For a period between 2008 and 2010, ACInet is calculated as a function of the cloud liquid water path, temperature, altitude, specific humidity, and lower tropospheric stability. For all data, ACInet averages 0.12 ± 0.02 for cloud-droplet effective radius and 0.16 ± 0.02 for cloud optical depth. It increases with specific humidity and lower tropospheric stability and is highest when pollution concentrations are low. Carefully controlling for meteorological conditions we find that the liquid water path of arctic clouds does not respond strongly to aerosols within pollution plumes. Or, not stratifying the data according to meteorological state can lead to artificially exaggerated calculations of the magnitude of the impacts of pollution on arctic clouds.

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We analyze interactions of Arctic clouds with pollution plumes that have been transported long distances from midlatitudes. Constraining for meteorological state, we find that pollution decreases cloud-droplet effective radius and increases cloud optical depth. The impact is highest when the atmosphere is particularly humid and/or stable suggesting that aerosol–cloud interactions depend on the Arctic's climate.
We analyze interactions of Arctic clouds with pollution plumes that have been transported long...