Impacts of Wildfire Smoke on Cirrus Cloud Formation

The increasing prevalence of wildfire smoke layers in the upper troposphere and lower stratosphere, likely driven by climate change, highlights their growing influence on the climate system. These smoke plumes travel across continents affecting climate through multiple pathways, emphasizing the need for their accurate representation in global climate models (GCMs). Among these pathways, this study focuses on the role of wildfire smoke particles in cirrus cloud formation by acting as efficient ice-nucleating particles (INPs).

The mechanisms governing cirrus cloud formation—whether dominated by homogeneous freezing or a competition with heterogeneous ice nucleation—determine their microphysical and optical properties, as well as their role in seeder-feeder and precipitation processes. Recent ground-based lidar and radar studies (e.g., Mamouri et al., 2023; Ansmann et al., 2024) provide evidence that aged wildfire smoke particles can trigger heterogeneous ice nucleation. However, their limited temporal and spatial coverage constrains our understanding of the broader-scale impacts of wildfire-induced cirrus, thereby complicating the development of reliable parameterizations for GCMs.

In this study, we seek to address this limitation by leveraging spaceborne observations to investigate the relationship between wildfire smoke and cirrus cloud formation. Potential smoke INPs are retrieved using the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) level 2 V4.51 data products, while in-cloud ice crystal number concentrations (ICNCs) are derived from the DARDAR-Nice (liDAR–raDAR-Number concentration of ICE particles) product. By integrating these datasets with global reanalysis data, we analyze multiple large wildfire events across both hemispheres, which help uncover the large-scale and seasonal characteristics of wildfire-induced cirrus. With wildfires becoming increasingly frequent and intense under a warming climate, understanding how smoke influences the occurrence and properties of cirrus clouds is critical for improving the accuracy of future climate projections.

 

Ansmann, A., Jimenez, C., Roschke, J., Bühl, J., Ohneiser, K., Engelmann, R., Radenz, M., Griesche, H., Hofer, J., Althausen, D., Knopf, D. A., Dahlke, S., Gaudek, T., Seifert, P., and Wandinger, U.: Impact of wildfire smoke on Arctic cirrus formation, part 1: analysis of MOSAiC 2019–2020 observations, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2024-2008, 2024

Mamouri, R.-E., Ansmann, A., Ohneiser, K., Knopf, D. A., Nisantzi, A., Bühl, J., Engelmann, R., Skupin, A., Seifert, P., Baars, H., Ene, D., Wandinger, U., and Hadjimitsis, D.: Wildfire smoke triggers cirrus formation: lidar observations over the eastern Mediterranean, Atmos. Chem. Phys., 23, 14097–14114, https://doi.org/10.5194/acp-23-14097-2023, 2023