Liquid Containing Clouds at the North Slope of Alaska Demonstrate Sensitivity to Local Industrial Aerosol Emissions. Issue 17 (2nd September 2021) - Maahn, Maximilian
Abstract: Cloud condensation nucleus control alter cloud solar albedo through cloud droplet size. Here, we leverage anthropogenic emissions at the North Slope of Alaska as a natural laboratory to study relationships between aerosols and Arctic liquid‐containing clouds. Averaging 14 years of MODIS observations, we found a reduction in temporally averaged cloud effective radius ( r e ) of up to 1.0 μm related to localized pollution. Pronounced regional gradients in cloud frequency of occurrence and liquid water path prohibit the detection of potential changes of these variables. Observed changes of r e alter radiative fluxes and increase cloud‐reflected shortwave radiation by up to 0.8 W m − 2 in the Prudhoe Bay area for the period covered by observations (April–September). Due to the frequent occurrence of liquid‐containing clouds, this implies that enhanced local emissions in Arctic regions can impact climate processes. Plain Language Summary: The interactions between aerosols and clouds are still not fully understood despite their importance for the Earth's weather and climate. Cloud condensation nuclei (CCN) are a type of aerosol particles that control cloud droplet size and the brightness of clouds. Their impact on other cloud properties is unclear. Here, we leverage industrial emissions at the North Slope of Alaska as a natural laboratory to study relationships between aerosols and Arctic liquid containing clouds. We found a notable reduction in cloud droplet size, but strong local gradients prohibit quantifying an impact on other cloud properties. The change in cloud droplet size is sufficient to make the clouds brighter. Because the frequent occurrence of liquid‐containing clouds in the Arctic, this shows a potential impact of local industrial emissions on climate processes. Key Points: Localized pollution reduces cloud droplet size in the Prudhoe Bay region The reduced droplet size increases cloud‐reflected shortwave radiation up to 0.8 W/m 2 Strong regional gradients prohibit an analysis of pollution impact on cloud frequency or liquid water content