Characterisation of low-base and mid-base clouds and their thermodynamic phase over the Southern and Arctic Ocean

• Main Authors: Dietel, Barbara, Sourdeval, Odran, Hoose, Corinna
• Format: Text
• Language: English
• Published: 2023
• Subjects: Arctic; Southern Ocean; Arctic Ocean; Sea ice
• Online Access: https://doi.org/10.5194/egusphere-2023-2281; https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2281/

The thermodynamic phase of clouds in low and middle levels over the Southern Ocean and the Arctic Ocean is poorly known, leading to uncertainties in the radiation budget in weather and climate models. To improve the knowledge of the cloud phase, we analyse two years of the raDAR-liDAR (DARDAR) dataset based on active satellite instruments. We classify clouds according to their base and top height and focus on low-, mid- and mid-low-level clouds as they are most frequent in the mixed-phase temperature regime. Low-level single-layer clouds occur in 22–26 % of all profiles, but single-layer clouds spanning the mid-level also amount to approx. 15 %. Liquid clouds show mainly a smaller vertical extent, but a horizontally larger extent compared to ice clouds. The results show the highest liquid fractions for low-level and mid-level clouds. Two local minima in the liquid fraction are observed around cloud top temperatures of -15 °C and -5 °C. Mid-level and mid-low-level clouds over the Southern Ocean and low-level clouds in both polar regions show higher liquid fractions if they occur over sea ice compared to open ocean. Low-level clouds and mid-low-level clouds with high sea salt concentrations, used as a proxy for sea spray, show reduced liquid fractions. In mid-level clouds, dust shows the largest correlations with liquid fraction with a lower liquid fraction for a higher dust aerosol concentration. Low-level clouds clearly show the largest contribution to the shortwave cloud radiative effect in both polar regions followed by mid-low-level clouds.