Seasonal impact of dynamics and turbulence on cloud formation over the Western North Atlantic

Understanding cloud formation processes and their influence on the Earths climate system are fundamental and pose a considerable uncertainty to current climate predictions. Here we investigate the seasonal impact of aerosols and dynamics on cloud formation in the Western North Atlantic Ocean (WNAO) boundary layer from an in-situ perspective. The WNAO exhibits an anti-correlated seasonal cycle of cloud number concentration Nc and cloud condensation nuclei concentration NCCN at cloud base with 20% less Nc and 50% more NCCN in summer (August) compared to winter (February-March). Low level clouds were measured during the Aerosol Cloud meTereology Interactions oVer the western ATlantic Experiment (ACTIVATE) campaign in winter, spring and summer 2020 and 2021. The cloud data are grouped with respect to their NCCN into a clean, medium polluted and high polluted environment. The updrafts w in cloud base correlate with the Nc cycle and are around 30% lower in summer. Through a statistical approach the impact of the updraft speed is quantified and presented for each group in the different seasons.