Impact of Canadian wildfires on aerosol and ice clouds in the early-autumn Arctic

Cloud particle phase is an important controlling factor for the Earth's surface heat budget, through the radiative balance. Thus, it exerts a strong influence on climate change in the Arctic. Aerosols transported from lower latitudes modify Arctic cloud properties, including cloud phase. In this study, we investigated ice cloud formation and high aerosol concentrations over the Arctic Ocean using a combination of observations obtained by an Arctic voyage, reanalysis data, and backward trajectory analyses. On 12 September 2023, in an atmospheric river over the Arctic Ocean, ice clouds at temperatures warmer than −15 °C were observed in the middle troposphere by a Cloud Particle Sensor sonde. In the lower troposphere, a particle counter onboard a drone detected particle counts two orders of magnitude higher than the voyage average. Backward trajectories indicated that a lower tropospheric air mass with a high concentration of organic carbon (OC) aerosols over northern and coastal western Canada, where wildfire-induced OC emissions were evident, reached the mid-troposphere over the Arctic Ocean. These results suggest that OC aerosols from severe Canadian wildfires in the summer of 2023 acted as ice-nucleating particles for ice cloud formation under high-temperature conditions exceeding −15 °C over the Arctic Ocean. • Vertical profiling of clouds and aerosols was conducted in the Arctic Ocean in 2023. • A particle counter on a drone recorded high-aerosol-concentration events. • Canadian wildfire aerosols would influence the Arctic ice cloud formation.