Microphysical and thermodynamic phase analyses of Arctic low-level clouds measured above the sea ice and the open ocean in spring and summer

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Moser, Manuel, Voigt, Christiane, Jurkat-Witschas, Tina, Hahn, Valerian, Mioche, Guillaume, Jourdan, Olivier, Dupuy, Régis, Gourbeyre, Christophe, Schwarzenboeck, Alfons, Lucke, Johannes, Boose, Yvonne, Mech, Mario, Borrmann, Stephan, Ehrlich, André, Herber, Andreas, Lüpkes, Christof, Wendisch, Manfred
• Format: Text
• Language: English
• Published: 2023
• Subjects: Arctic; Arctic Ocean; Greenland; Svalbard; Alfred Wegener Institute; Fram Strait; Sea ice
• Online Access: https://doi.org/10.5194/acp-23-7257-2023; https://acp.copernicus.org/articles/23/7257/2023/

Airborne in situ cloud measurements were carried out over the northern Fram Strait between Greenland and Svalbard in spring 2019 and summer 2020. In total, 811 min of low-level cloud observations were performed during 20 research flights above the sea ice and the open Arctic ocean with the Polar 5 research aircraft of the Alfred Wegener Institute. Here, we combine the comprehensive in situ cloud data to investigate the distributions of particle number concentration N , effective diameter D eff , and cloud water content CWC (liquid and ice) of Arctic clouds below 500 m altitude, measured at latitudes between 76 and 83 ∘ N. We developed a method to quantitatively derive the occurrence probability of their thermodynamic phase from the combination of microphysical cloud probe and Polar Nephelometer data. Finally, we assess changes in cloud microphysics and cloud phase related to ambient meteorological conditions in spring and summer and address effects of the sea ice and open-ocean surface conditions. We find median N from 0.2 to 51.7 cm −3 and about 2 orders of magnitude higher N for mainly liquid clouds in summer compared to ice and mixed-phase clouds measured in spring. A southerly flow from the sea ice in cold air outbreaks dominates cloud formation processes at temperatures mostly below −10 ∘ C in spring, while northerly warm air intrusions favor the formation of liquid clouds at warmer temperatures in summer. Our results show slightly higher N in clouds over the sea ice compared to the open ocean, indicating enhanced cloud formation processes over the sea ice. The median CWC is higher in summer (0.16 g m −3 ) than in spring (0.06 g m −3 ), as this is dominated by the available atmospheric water content and the temperatures at cloud formation level. We find large differences in the particle sizes in spring and summer and an impact of the surface conditions, which modifies the heat and moisture fluxes in the boundary layer. By combining microphysical cloud data with thermodynamic phase information from the Polar ...