For the western United States, summer is wildfire season and where there is fire, there is smoke. Wildfire smoke includes airborne particles that can act as nuclei for forming individual droplets in clouds. A team of researchers, funded in part by CPO’s Atmospheric Chemistry, Carbon Cycle, and Climate (AC4) program, recently published a study in Geophysical Research Letters showing how these smoke-influenced clouds differ from their clean air counterparts, with complex implications for our weather and climate. They found that clouds were strongly influenced by smoke across the western United States, forming with more, smaller droplets.
Clouds over the western United States were sampled as part of the WE-CAN field campaign via airborne instruments during the wildfire season in summer of 2018. Researchers compared the properties of the clouds to those of smoke aerosols to understand how smoke particles influence small cumulus clouds.
The research team found that, on average, sampled clouds had around five times as many droplets compared to clouds not influenced by smoke, though the average individual droplet was about half its normal size. Small droplet sizes mean that smoky clouds are expected to reflect more light and produce less rain than clouds in smoke-free air. However, the research team noted that when considering climate impacts beyond those to the clouds themselves, the results are decidedly more complex and would require a detailed regional model built specifically to explore aerosols, cloud microphysics, and radiation.