Arctic aerosols affect cloud properties and climate. However, the magnitudes and mechanisms are uncertain, as are how aerosol-cloud relationships might change in a rapidly warming environment. We assessed some of the complex relationships between aerosols, surface, and meteorology in the relatively pristine summertime Arctic and quantified resulting impacts on clouds using CloudSat/CALIPSO data, AIRS relative humidity and temperature, plus MERRA-2 aerosol and meteorological reanalysis products. In line with previous studies, dust aerosol layers over the summertime Arctic sea ice are associated with icier clouds. However, summertime dust-associated cloud glaciation is uncommon at temperatures >-10 ºC and not likely at lower altitudes in the summer. We use DMS concentrations as a proxy for marine new particle formation. When DMS is elevated, open ocean clouds near the surface (0.6-1.5 km) are up to 12% more prevalent. These findings allow us to make some educated guesses about where key processes are occurring, such as ice nucleation from dust, and to more effectively prioritize aircraft targeting in future field campaigns, such as ARCSIX.

Cloud phase has important impacts on Arctic surface temperatures, and there is substantial circumstantial evidence that dust aerosols have strong impacts on cloud phase over the Arctic on a regional scale. We used seven years of satellite observations and model and reanalysis products to control for co-varying meteorology, and to assess how dust and other aerosols impact cloud phase over the summertime sea ice. We focus on clouds at 3 km, where dust modeling is most accurate. Dust aerosols caused about 4.5% of clouds below -15 °C to change phase, with smaller effects at higher temperatures. Sulfate has a smaller impact on cloud phase. Dust is associated with cloud-mediated surface cooling of up to a 6.3 W m-2 below single-layer clouds at ~3 km in June. Lastly, we discuss the optimal meteorological conditions for future in situ studies to maximize insight into the mechanisms driving the observed dust effects.

Mixed-phase clouds are ubiquitous in the Arctic and play a critical role in Earth’s energy budget at the surface and top of the atmosphere. These clouds typically occupy the lower and midlevel troposphere and are composed of purely supercooled liquid droplets or mixtures of supercooled liquid water droplets and ice crystals. Here, we review progress in our understanding of the factors that control the formation and dissipation of Arctic mixed-phase clouds, including the thermodynamic structure of the lower troposphere, warm and moist air intrusions into the Arctic, large-scale subsidence and aerosol particles. We then provide a brief survey of numerous Arctic field campaigns that targeted local cloud-controlling factors and follow this with specific examples of how the Arctic Cloud Observations Using airborne measurements during polar Day (ACLOUD)/ Physical feedback of Arctic PBL, Sea ice, Cloud And AerosoL (PASCAL) and Airborne measurements of radiative and turbulent FLUXes of energy and momentum in the Arctic boundary layer (AFLUX) field campaigns that took place in the vicinity of Svalbard in 2019 were able to advance our understanding on this topic to demonstrate the value of field campaigns. Finally, we conclude with a discussion of the outlook of future research in the study of Arctic cloud-controlling factors and provide several recommendations for the observational and modelling community to advance our understanding of the role of Arctic mixed-phase clouds in a rapidly changing climate.