The Arctic experiences intrusions of high aerosol levels termed “Arctic haze,” especially between winter and late spring. Strong east-west pressure gradients can cause a poleward transport of pollution from mid latitudes, primarily from Eurasia. This haze may play an important role in affecting cloud properties, and hence their radiative impacts at the surface, in winter.
Scientists used 4 years of observations from the Atmospheric Radiation Measurement (ARM) Climate Research Facility measurement site in Barrow, Alaska, to determine the indirect effects of Arctic haze pollution on surface cloud radiative forcing by low-level clouds in the Arctic. The study shows that the cloud radiative impact on the surface is a net warming effect between October and May and a net cooling in summer. During episodes of high surface haze aerosol concentrations and cloudy skies, both the net warming and net cooling are amplified, ranging from +12.2 Wm-2 in February to -11.8 Wm-2 in August. In liquid clouds, approximately 50% to 70% of this change is caused by changes in cloud particle size, with the remainder caused by unknown atmospheric feedbacks that increase cloud water path. While the yearly averaged warming and cooling effects nearly cancel, the timing of the forcing may be a relevant control of the amplitude and timing of sea ice melt.
Reference: Zhao, C., and T. J. Garrett. 2015. “Effects of Arctic Haze on Surface Cloud Radiative Forcing,” Geophysical Research Letters 42(2), 557–64. DOI: 10.1002/2014GL062015. (Reference link)
Contact: Sally McFarlane, SC-23.1, (301) 903-0943
SC-23.1 Climate and Environmental Sciences Division, BER
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