11 May 2023
 | 11 May 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

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

Simon Kirschler, Christiane Voigt, Bruce E. Anderson, Gao Chen, Ewan C. Crosbie, Richard A. Ferrare, Valerian Hahn, Johnathan W. Hair, Stefan Kaufmann, Richard H. Moore, David Painemal, Claire E. Robinson, Kevin J. Sanchez, Amy J. Scarino, Taylor J. Shingler, Michael A. Shook, Kenneth L. Thornhill, Edward L. Winstead, Luke D. Ziemba, and Armin Sorooshian

Abstract. Due to their fast evolution and large variability, the accurate representation of boundary layer clouds in current climate models remains a challenge. One of the regions with large intermodel spread of 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. 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 17209 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 nuclei 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 in the western edge of cyclones (post-cyclonic). In contrast, a dominant summer anticyclone is concomitant with the occurrence of shallow cumulus clouds and lower cloud coverage. The evaluation of boundary layer clouds and precipitation in the Nliquid-ED phase space sheds light on liquid, mixed-phase, and ice cloud properties and helps to understand their formation. Ice and liquid precipitation, often masked in cloud statistics by high abundance of liquid clouds, is often observed throughout the cloud. The ACTIVATE in-situ cloud measurements provide a wealth of cloud information useful for assessing airborne and satellite remote sensing product, for global climate and weather model evaluations, and for dedicated process studies that address precipitation and aerosol-cloud interactions.

Simon Kirschler et al.

Status: open (until 22 Jun 2023)

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Simon Kirschler et al.

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Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment Armin Sorooshian

Simon Kirschler et al.


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Short summary
In this study we present an overview of liquid and mixed-phase clouds and precipitation in the marine boundary layer over the western North-Atlantic Ocean. We compare microphysical properties of pure liquid clouds to mixed-phase clouds and show that the initiation of the ice phase in mixed-phase clouds promotes precipitation. The observational data presented in this study is well suited for investigating the processes that give rise to liquid and mixed-phase clouds, ice and precipitation.