Overview and statistical analysis of boundary layer clouds and precipitation over the western North-Atlantic Ocean

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Kirschler, Simon, Voigt, Christiane, Anderson, Bruce E., Chen, Gao, Crosbie, Ewan C., Ferrare, Richard A., Hahn, Valerian, Hair, Jonathan W., Kaufmann, Stefan, Moore, Richard H., Painemal, David, Robinson, Claire E., Sanchez, Kevin J., Scarino, Amy Jo, Shingler, Taylor J., Shook, Michael A., Thornhill, Kenneth Lee, Winstead, Edward, Ziemba, Luke, Sorooshian, Armin
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2023
• Subjects: Wolkenphysik; North Atlantic
• Online Access: https://elib.dlr.de/198083/; https://elib.dlr.de/198083/1/acp-23-10731-2023.pdf; https://acp.copernicus.org/articles/23/10731/2023/

Due to their fast evolution and large natural variability in macro- and microphysical properties, the accurate representation of boundary layer clouds in current climate models remains a challenge. One of the regions with large intermodel spread in the Coupled Model Intercomparison Project Phase 6 ensemble is the western North Atlantic Ocean. Here, statistically representative in situ measurements can help to develop and constrain the parameterization of clouds in global models. To this end, we performed comprehensive measurements of boundary layer clouds, aerosol, trace gases, and radiation in the western North Atlantic Ocean during the NASA Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) mission. In total, 174 research flights with 574 flight hours for cloud and precipitation measurements were performed with the HU-25 Falcon during three winter (February–March 2020, January–April 2021, and November 2021–March 2022) and three summer seasons (August–September 2020, May–June 2021, and May–June 2022). Here we present a statistical evaluation of 16 140 individual cloud events probed by the fast cloud droplet probe and the two-dimensional stereo cloud probe during 155 research flights in a representative and repetitive flight strategy allowing for robust statistical data analyses. We show that the vertical profiles of distributions of the liquid water content and the cloud droplet effective diameter (ED) increase with altitude in the marine boundary layer. Due to higher updraft speeds, higher cloud droplet number concentrations (Nliquid) were measured in winter compared to summer despite lower cloud condensation nucleus abundance. Flight cloud cover derived from statistical analysis of in situ data is reduced in summer and shows large variability. This seasonal contrast in cloud coverage is consistent with a dominance of a synoptic pattern in winter that favors conditions for the formation of stratiform clouds at the western edge of cyclones (post-cyclonic). In contrast, a ...